Flying Fast Jets: Human Factors and Performance Limitations (Human Factors in Defence) 9781409467939, 9781409467946, 1409467937

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Flying Fast Jets

Human Factors in Defence Series Editors: Dr Don Harris, Coventry University, UK Professor Neville Stanton, University of Southampton, UK Dr Eduardo Salas, University of Central Florida, USA Human factors is key to enabling today’s armed forces to implement their vision to ‘produce battle-winning people and equipment that are fit for the challenge of today, ready for the tasks of tomorrow and capable of building for the future’ (source: UK MoD). Modern armed forces fulfil a wider variety of roles than ever before. In addition to defending sovereign territory and prosecuting armed conflicts, military personnel are engaged in homeland defence and in undertaking peacekeeping operations and delivering humanitarian aid right across the world. This requires top class personnel, trained to the highest standards in the use of first class equipment. The military has long recognised that good human factors is essential if these aims are to be achieved. The defence sector is far and away the largest employer of human factors personnel across the globe and is the largest funder of basic and applied research. Much of this research is applicable to a wide audience, not just the military; this series aims to give readers access to some of this high quality work. Ashgate’s Human Factors in Defence series comprises of specially commissioned books from internationally recognised experts in the field. They provide in-depth, authoritative accounts of key human factors issues being addressed by the defence industry across the world.

Flying Fast Jets

Human Factors and Performance Limitations

David G. Newman MB, BS, DAvMed, MBA, PhD, FRAeS, FAsMA, FACAsM, FAICD, FAIM Swinburne University, Melbourne, Australia

© David G. Newman 2014 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the publisher. David G. Newman has asserted his right under the Copyright, Designs and Patents Act, 1988, to be identified as the author of this work. Published by Ashgate Publishing Limited Ashgate Publishing Company Wey Court East 110 Cherry Street Union Road Suite 3-1 Farnham Burlington, VT 05401-3818 Surrey, GU9 7PT USA England www.ashgate.com British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library The Library of Congress has cataloged the printed edition as follows: The Library of Congress Cataloging-in-Publication Data has been applied for. ISBN: 978-1-4094-6793-9 (hbk) ISBN: 978-1-4094-6794-6 (ebk – PDF) ISBN: 978-1-4094-6795-3 (ebk – ePUB)

IV

Printed in the United Kingdom by Henry Ling Limited, at the Dorset Press, Dorchester, DT1 1HD

Contents List of Figures Abbreviations   Foreword   Preface   Acknowledgements  

ix xi xv xvii xix

1

The Fast Jet Environment   Fighter Operations   Definition of a Fighter Aircraft   Fighter Aircraft Generations   Weapons Systems   Guidance system   Warhead   Propulsion system    Fighter Tactics   Fighter Missions   Fighter sweep   Point defence   Strike escort   Intercepts   Attack Aircraft Operations   Definition of an Attack Aircraft   Weapons Systems   Attack Missions   Attack Aircraft Tactics   Super-Agile Flight  

1 1 1 2 3 4 6 6 6 11 11 11 12 12 12 12 13 14 15 16

2

Altitude   Atmospheric Physics   Low Pressure   Hypoxia   Incidence   Signs and Symptoms   Tolerance to Hypoxia   Time of Useful Consciousness   Training   Cockpit Pressurisation   The Fast Jet Pressurisation System  

17 17 18 20 21 22 24 25 25 25 26

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Cockpit Pressurisation Failure   The Oxygen System   Other Altitude Problems   Decompression Illness   Ebullism   Case Study  

27 28 30 30 31 31

3

Acceleration   The Physics of G   Magnitude of G   Direction of G   Physiological Effects of G   Visual Effects of +Gz   A-LOC   G-LOC   Prevalence of G-LOC   Clinical G Problems   +Gz-induced Neck Injuries   Respiratory Effects   Miscellaneous G Effects   G Tolerance   G Protection Measures   G-Suits   Anti-G Straining Manoeuvre   Positive Pressure Breathing   Centrifuge Training   A Glimpse into the High G Future   Case Study  

33 33 34 34 36 37 38 38 40 41 41 41 42 43 44 44 45 46 47 47 48

4

Spatial Disorientation   Definitions     Type I (Unrecognised)   Type II (Recognised)   Type III (Incapacitating)   Prevalence of Spatial Disorientation   Underlying Mechanisms   Illusions by Phase of Flight   Take-off   In-flight Phase   Landing   Risk Factors     Pilot Factors   Aircraft Factors   Operational Factors  

49 49 49 50 50 50 51 54 54 55 58 59 59 60 61



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Countermeasures   Training   Technology   Case Study  

61 61 62 63

5

Life Support Equipment   The Flight Suit   The Flight Helmet   Impact Protection   Helmet-Mounted Sighting and Display Systems   Advanced Helmet Design Options   The Oxygen Mask   The G-Suit   Chest Counterpressure Garment   The Survival Vest   The Immersion Suit   The Liquid Cooling Garment   The CBRN Ensemble   Anthropometry   Aircrew Equipment Integration  

65 65 66 68 69 70 71 72 73 74 74 75 76 77 78

6

Situational Awareness   Defining Situational Awareness      The Fast Jet Cockpit    Sensor Systems   Aircraft Performance Sensors   Tactical Situation Sensors   Radar   Infra-red search and track    Targeting FLIR   Threat detection   Displays     Head-Up Displays   Helmet-Mounted Display and Sighting Systems   Joint Helmet-Mounted Cueing System (JHMCS)   Night Vision Goggles   Challenges and Limitations   Sensor Fusion    

81 81 83 86 86 86 87 88 88 89 89 89 91 92 92 94 95

7

Escape   History of Escape from Aircraft     The Modern Ejection Seat     Anatomy   Performance Specifications  

97 97 99 99 100

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8

Typical Ejection Sequence   Ejection Posture   Survival Outcomes   Ejection Injuries    The Catapult Phase   The Aircraft Separation Phase   The In-Seat Flight Phase   The Parachute Descent Phase   The Landing Phase   Post-Ejection Considerations   Next-Generation Seats   Case Study  

101 103 103 106 106 108 109 109 109 110 111 112

Selection and Training   Selecting the Fast Jet Pilot   Review of Selection Methodologies   Training the Fast Jet Pilot   Fast Jet Flight Training   Use of Flight Simulators   Human Factors Training   Ejection seat training   Spatial disorientation training   Hypoxia training   Centrifuge training   NVG training  

115 115 116 118 118 121 122 124 124 125 127 129

References   Index  

131 147

List of Figures 1.1 1.2 1.3 1.4 2.1 3.1 4.1 5.1 6.1 6.2 7.1 7.2 7.3 8.1

Weapon Employment Zone   Air-to-air missile   Generic V-n diagram for a fighter aircraft   High Yo-Yo manoeuvre   Oxygen-haemoglobin dissociation curve   Gz environment of a fighter during air combat manoeuvring   Spatial orientation mechanisms   Life support equipment as worn by a fast jet pilot   Typical fast jet cockpit layout   Typical fast jet Head-Up Display   Ejection seat    Ejection survival outcomes   Ejection vertebral fracture distribution in RAAF Macchi aircraft   Fast jet pilot selection and training pipeline  

5 5 8 10 20 35 52 66 85 90 99 104 107 119

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Abbreviations ACM ADI AESA AFOQT AGSM AGV AIS A-LOC AOA AR ASP ASRAAM ATAGS AWACS BAT BFM CAP CAS CBRN CCPG CF CFIT COMBAT EDGE DAS DCI DDI DFS DVI ECGS ECS ECM EPT FAC FCAGT FLIR g G

Air Combat Manoeuvring Attitude Direction Indicator Active Electronically-Scanned Array Air Force Officer Qualifying Test Anti-G Straining Manoeuvre Anti-G Valve Attack and Identification System Almost Loss of Consciousness Angle of Attack Active Radar Aircrew Services Package Advanced Short-Range Air-to-Air Missile Advanced Technology Anti-G Suit Airborne Warning And Control System Basic Attributes Test Basic Fighter Manoeuvres Combat Air Patrol Close Air Support Chemical, Biological, Radiological and Nuclear Chest Counterpressure Garment Canadian Forces Controlled Flight Into Terrain Combined Advanced Technology Enhanced Design Anti-G Ensemble Distributed Aperture System Decompression Illness Digital Display Indicators Dynamic Flight Simulation Direct Voice Input Extended Coverage G-Suit Environmental Conditioning System Electronic Countermeasures Effective Performance Time Forward Air Control Full Coverage Anti-G Trouser Forward-Looking Infra-Red Acceleration due to Earth’s Gravity Multiples of g; Gravitational constant

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GCAS Ground Collision Avoidance System GCI Ground-Controlled Intercept G-LOC G-induced Loss of Consciousness GMTI Ground Moving Target Identification GOR Gradual Onset Run GPS Global Positioning System GPWS Ground Proximity Warning System HARM High-speed Anti-Radiation Missile HMD Helmet-Mounted Display HOBS High Off-Boresight Seeker HOTAS Hands On Throttle And Stick HUD Head-Up Display HVI Helmet Vehicle Interface HVR Hypoxic Ventilatory Response ICP Integrated Control Panel IFF Identification Friend or Foe IMC Instrument Meteorological Conditions IQ Intelligence Quotient IR Infra-Red IRST Infra-Red Search And Track JDAM Joint Direct Attack Munition JHMCS Joint Helmet Mounted Cueing System JSUPT Joint Specialised Undergraduate Pilot Training LANTIRN Low-Altitude Navigation and Targeting Infra-Red Night LCD Liquid Crystal Display LCG Liquid Cooling Garment LOX Liquid Oxygen LPI Low Probability of Intercept LWR Laser Warning Receiver MAB Multi-dimensional Aptitude Battery MAWS Missile Approach Warning System MDC Miniature Detonating Cord MFD Multi-Function Display mmHg Millimetres of mercury NBC Nuclear, Biological and Chemical NTCR Non-Cooperative Target Recognition NVG Night Vision Goggles OBOGS On-Board Oxygen Generation System OCU Operational Conversion Unit PBG Positive Pressure Breathing for G Protection PCSM Pilot Candidate Selection Method PFD Primary Flight Display PSI Per Square Inch RAAF Royal Australian Air Force

Abbreviations

RAF Royal Air Force RWR Radar Warning Receiver ROR Rapid Onset Run SA Situational Awareness SACM Simulated Air Combat Manoeuvring profile. SD Spatial Disorientation SEAD Suppression of Enemy Air Defences STANAG NATO Standardisation Agreement TAWS Terrain Awareness Warning System TDC Target Designator Controller TSAS Tactile Situation Awareness System TUC Time of Useful Consciousness TVC Thrust Vectoring Control UFC Up-Front Controller USAF United States Air Force USN United States Navy UV Ultra-Violet Vmin Minimum flying speed WEZ Weapon Employment Zone WMD Weapons of Mass Destruction WSO Weapons Systems Officer

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Foreword Fast jets and fighter pilots are a relatively new phenomenon in the evolution of man and the tools of combat. Fighter aircraft have repeatedly played a pivotal role in modern joint military operations. In fact, ground and maritime operations have become almost unthinkable without air superiority being first gained and then maintained over the battlefield by fighter aircraft and supporting systems. It is inevitable therefore that folklore of superhuman skills and performance is attributed to the men and women who fly those fast jets. Pilots are handpicked for their mental and physical skills even before they are selected to become fighter pilots. Only the top-performing graduates from pilot courses are selected for training on fighter aircraft. As the training is expensive, costly failure is reduced through selection and continuous assessment in specially tailored initial and operational flying courses. Development of a combat-ready fighter pilot takes years of training, and the full potential of an individual is usually reached after two squadron postings, separated by a secondary qualification as an instructor or test pilot. The development of an individual to the point where he or she is trusted with the lead of a large formation of fighters in a highly dynamic three-dimensional air combat environment defines the select ‘A-Category Fighter Pilot’ qualification of an individual. Such leadership in combat also demonstrates the ultimate concept of ‘crew coordination’. It is also an achievement that contains highly perishable skills that require regular exposure. All the selection and training of a modern fighter pilot is not able to overcome the basic limitations of man; his dependence on oxygen and limited tolerance to operating under high G loads are but a couple of the obvious ones. These and other limitations require special systems and training to ensure the pilot is as effective as possible in air combat. That said, the man-in-the-cockpit concept of fighters seems to have a limited future with unmanned combat aircraft already a reality in some tailored operations. However, the fielding of fourth- and fifth-generation aircraft is testimony to the fact that man will continue to play a significant role in the cockpit of fast jets for decades to come. This book outlines the challenges faced by man in conquering the air combat environment. All challenges are of course shared with aviators in any domain, but some like G loads and the maintenance of situational awareness regularly expose the fighter pilot to the limits of what is humanly possible. In my career as a fighter pilot and test pilot, I experienced most of the human factors challenges discussed in this book. In over 4,000 hours of flying fighters such as the Mirage and F/A-18 aircraft I experienced the detached-from-earth feeling and oxygen system problems associated with high-altitude flight, high speed and high G loads, as well as situational awareness challenges and disorientation. On two separate

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occasions I successfully ejected from single-engine fighter aircraft, both suffering from engine problems. I have known Dr David Newman as a flight surgeon for many decades and had the pleasure of working with him over the years. In this outstanding book David distils his research into and expert knowledge of the human factor challenges in the fast jet environment. The book is written in an attractive and easily understood style. I commend it to all who are interested in the human challenges of aviation and as a textbook for professional pilots. John W. Kindler AO, AFC Air Vice-Marshal

Preface This book is not designed to be an exhaustive treatise on air combat tactics. No reader should be under the illusion that at the end of this book they will know all there is to know about being a fast jet pilot. My goal in writing this book is to focus on the human element of being a fast jet pilot, in terms of the human factors challenges and performance limitations that fast jet pilots deal with on a daily basis while operating in their unique environment. How they deal with these challenges is a key element of this book. In writing this book, I have attempted to capture some of the complexity of the fast jet environment, particularly for those readers who have not had the opportunity to experience it first-hand. The fast jet environment is unique, and involves high speed, high altitude, high G-loads, high workload, and the need for rapid decision-making. Fast jet pilots must maintain situational awareness in a dynamic and frequently changing environment, where the consequences of getting this wrong can be disastrous. Flying fast jets is a high-risk endeavour, with the training almost as dangerous as the combat operations the training helps prepare the crew for. There are very few occupations like that of a fast jet pilot. The human factors and performance limitations involved in flying fast jets include altitude exposure, high G-loads, the potential for spatial disorientation, ejection issues, the myriad life-support equipment required, situational awareness and the human–machine interface, and the challenges involved in selection and training. In discussing all of these, this book will hopefully give the reader a sense of the high level of technical knowledge that a modern fast jet pilot requires, and the complexity of the manoeuvring environment in which they must operate the aircraft in order to achieve the mission objectives. As an aviation medicine specialist, my experience of the fast jet environment spans almost the full spectrum, whether while flying or in support. My RAAF service allowed me to fly regularly in aircraft such as the Macchi MB326H, the Hawk, and the F/A-18 Hornet. As a qualified civilian pilot and military flight surgeon, I was given the even rarer opportunity to personally fly these high performance aircraft, including a Harrier T10 while on exchange with the RAF. There have been aircraft emergencies, including departure from controlled flight and main tyres blowing on touchdown. On three occasions I thought I would have to eject. Two of my squadron mates did, following a mid-air collision during a 2 versus 1 air combat training mission in 1994. I was involved in their rescue and recovery. Being winched down from the rescue helicopter, retrieving both of them and then taking care of their medical needs on return to the base was professionally and personally very rewarding. This was even more so when they both returned to fast jet flying. I have had bird-strikes, including one during a low-

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level navigation flight in the UK in a Hawk (ironically). Then there were the days when on completion of the mission and during the return to base we would fly upside down for a while, just because we could. I have experienced the exhilaration of high speed, low-level flight, the beauty of high-altitude flight (including to 50,000 ft in an F/A-18), the thrill of being supersonic, and the physical and mental demands of high +Gz air combat manoeuvring. Not bad for a doctor. To the fast jet pilots who encouraged this, gave me the required instruction, and made it all possible, I will forever be grateful. In my mind I have seen the pinnacle of flying, and my life has been richer for it. It is my hope that as you read this book you will gain a better understanding of the fast jet environment and all its inherent complexity, and of the unique challenges that a modern fast jet pilot must face. If at the end of this book you have a new-found appreciation of what a fast jet pilot does for a living, then my work is done. Dr David G. Newman Melbourne Australia April 2014

Acknowledgements I would like to thank the many people who have helped make this book possible. I am enormously grateful to all the fast jet pilots that I have had the pleasure of flying with for introducing me to the world of fast jet operations. They not only allowed me to personally fly some incredible aircraft, and in doing so have some of the best moments of my professional life, but they also showed me how potent a weapon a fast jet can be in the hands of a highly trained pilot. I have flown with many fast jet pilots, in both the RAAF and also with the RAF, and working with them so closely has been an honour and a privilege. They know who they are, but I want to thank them anyway: Baz, Noz, JK, McFly, JC, Lono, Chipper, Kitch, PV, Nocka, Spot, Kombi, Nev, Ronnie, Killer, Bruce, Crusher, TC, Chase, P-squared, Leroy, Patch, Sonic, Westy, Mel, Gumby, Stuey, Neil, JQ, Pudz, Phil, Tim, Markie, Beewah, Lej, Mookeye, Frawls and JB. I would like to particularly thank Air Vice-Marshal John Kindler, AO, AFC, for so readily agreeing to write the foreword to this book. I am very grateful for his generous support, both now and during the time we served together. Thanks also to Air Vice-Marshal (retired) Graeme Moller and Air Commodore Warren Harrex, for the support and encouragement they gave to a young RAAF medical officer conducting research into ejection injuries, and to Professor Robin Callister, for being a great supervisor, friend and colleague during my PhD research into the effects on cardiovascular physiology of high +Gz exposure. Finally, I would like to thank my wonderful wife Fiona, and my talented daughters Laura (who did many of the figures in the book) and Sarah. Their love, support and encouragement over many years have made this book possible.

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To Fiona, Laura and Sarah

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Chapter 1

The Fast Jet Environment The advent of the fast jet and the introduction of the air-to-air missile changed the nature of air combat. The modern fast jet has evolved considerably, and is a very capable aircraft. It is immensely strong, incredibly powerful, highly agile, and equipped with advanced weapons, avionics and sensor systems. The operational environment of the fast jet is unique and complex. The aircraft is typically flown by either a single pilot or a two-man crew of pilot and weapons systems operator. The aircraft may be flown as part of a formation package on tactical missions in a high-threat combat environment, or operate singly. It can carry a multitude of weapons, and in the case of multi-role aircraft such as the F/A-18 Hornet it can be loaded with both air-to-air and air-to-ground weapons. The purpose of this chapter is to give the reader a broad understanding of the fast jet environment, which will set the scene for the subsequent discussion of the human factors and performance limitations associated with flying the fast jets. This chapter will examine the aircraft involved, the weapons deployed, the missions conducted and the tactics employed. For ease of description, the fast jet environment is categorised in terms of fighter operations and attack operations. However, it must be borne in mind that increasingly a fast jet pilot will undertake both types of operation, rather than one or the other. Finally, a brief consideration of the super-agile fast jet will provide a look into the future of fast jet operations. Fighter Operations Definition of a Fighter Aircraft In simple terms, a fighter aircraft is designed to kill another aircraft. This opponent aircraft may be another fighter, or a high-value enemy asset such as a bomber, tanker or command and control aircraft. Owing to its inherent capabilities, a fighter aircraft may also be employed operationally to protect friendly aircraft assets, or to protect airspace from enemy intruders through interception duties. The fighter aircraft role has evolved substantially over time, and now often involves a multi-role scenario, where air-to-ground and attack activities are also part of the day-to-day life of a fighter pilot. In this section, the focus will be exclusively on the fighter role. This role involves achieving and maintaining air superiority or air dominance. These terms are often used interchangeably. In general, when operationally deployed in wartime, the main role for a fighter aircraft is to establish air superiority over a battlefield.

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Fighter Aircraft Generations There is no universally agreed definition of what constitutes a fighter generation. Indeed, there has been much discussion on this topic. In general terms, the following guidance is provided to help readers understand the evolution of the fast jet, especially given that the term ‘fifth-generation fighter’ is regularly used in the media these days. The phrase ‘fighter generations’ typically provides a useful framework to understand the evolution of the fighter aircraft since the introduction of the jet engine. Indeed, the leap from one generation of aircraft to the next has often resulted from a single piece of innovative technology (such as the introduction of the jet engine, or stealth technology). Generation 1 fighters represented the very early jet-engined fighters, such as the Me-262 and the F-80. Generation 2 fighters were a significant step up, marked by the advent of the swept wing. The incorporation of range-finding radar and the deployment of infra-red missiles also characterised the second generation fast jet. Examples include the F-86 Sabre and the MiG-15. Generation 3 fast jets were characterised by supersonic capabilities. On-board radars had evolved to include pulse radars, and the deployed weapons systems allowed these fighters to engage targets beyond visual range. Examples of Generation 3 fast jets include MiG-17 and MiG-21, the F-4 Phantom and the socalled ‘Century series’ jets such as the F-104, F-105 and so on. Generation 4 fighters had enhanced levels of manoeuvrability. The deployed weapons systems were substantially more capable than previous generation aircraft, with pulse-Doppler radar and missiles able to give a ‘look-down, shoot-down’ capability. Other technological developments included the HOTAS system – Hands On Throttle And Stick. This system was developed in recognition of the demands that the increasing manoeuvrability of the aircraft was putting on the pilot. The high G loads and increased agility meant that all necessary switches were repositioned on either the control column or throttle, so that under high G loads the fingers of the pilot were never far from the required switch (for example, radar cursor, weapons systems switches, and so on). This system thus allowed the pilot to fully exploit the increased agility of the Generation 4 aircraft without reducing its combat potential through an inability to operate an essential switch. Other technological improvements included the Heads-Up Display (HUD), which took all essential flight-based instrumentation and weapons system information and projected them onto a glass plate in direct line of sight of the pilot. These systems have continued to evolve into higher levels of sophistication, and are discussed in greater detail in Chapter 6. Aircraft in this generation include the F-15, the F-16, Mirage 2000 and the MiG-29. Ongoing technological enhancements and upgrade programmes resulted in progressively more agile and sophisticated fighters. These aircraft, while still categorised as fourth-generation aircraft, have also been classified as Generation 4+ or 4.5, to indicate that they are a step above the typical (and earlier) Generation 4 aircraft. These enhanced Generation 4 aircraft include the Eurofighter Typhoon,

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the Su-30, advanced versions of the F-16 and F/A-18, and the Dassault Rafale. These aircraft had greater levels of agility, but also incorporated significant features such as sensor fusion (see Chapter 6) and reduced radar signatures. The HOTAS and HUD systems of early Generation 4 fast jets have evolved further, resulting in helmet-mounted cueing systems. The development of other weapons systems advances such as active electronically scanned arrays and early low observability (stealth) technology were features of the Su-35 and the F-15 Super Eagle. As an entire category, therefore, Generation 4 contains most of the world’s currently flown fast jet aircraft. It must be remembered, of course, that a major avionics upgrade involving sensors, radars and weapons systems can be applied to an early generation fighter aircraft and lift it into a higher generation (at least from a war-fighting perspective). The aircraft in use with most air forces around the world today would be Generation 4. Generation 5 aircraft are the latest iterations of fighter aircraft technology, and by definition are only few in number. Many have either just recently entered service or are still in early production or advanced flight testing phases. These aircraft combine all-aspect stealth technology, with internal weapons carriage, extremely high levels of agility (to the super-agile level), full sensor fusion, integrated digital avionics, data linkages, and supercruise capability. Supercruise refers to the ability of an aircraft to fly at supersonic speeds for sustained periods of time without the use of afterburners (thus preserving fuel and reducing heat signatures). There are few examples of Generation 5 aircraft – the F-22 Raptor is in service with the USAF, and the multination F-35 Joint Strike Fighter is yet to enter service. Weapons Systems The choice of air-to-air weapons is considerable. In general, the choices narrow down to either guns or missiles. Within those two categories there is considerable choice, particularly in missile terms. Modern fast jets tend to be equipped with a cannon (known rather euphemistically as a gun). There is a large range of airto-air ordnance, a detailed discussion of which is beyond the scope of this book. However, air-to-air missiles have some common elements worth discussing, in order to give a sense to the reader of the sophisticated modern weapons technology available to the fast jet pilot. The early fighter aircraft were limited in their effectiveness by engine performance, structural strength and the weapons that they carried. These aircraft had relatively poor performance envelopes, particularly in terms of turning ability. The main armaments were guns, and in order to shoot their opponent they were forced to manoeuvre their aircraft into the rear quarter of the target aircraft. A circular chase would then develop, with both aircraft attempting to achieve this rear position first and maintain it long enough to fire effectively on their opponent. Although aircraft speeds and gun technology have both improved considerably, the same principles apply in fast jet operations. The use of the gun as a close-in weapon requires particular skills in guns tracking on the part of the fast jet pilot.

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The pilot must allow for the trajectory of the fired bullets, as well as the flight path of the target aircraft. The techniques involved will be considered later in this chapter under basic fighter manoeuvres. While a comprehensive analysis of air-to-air missile technology is beyond the scope of this book, it is worth discussing these important weapons systems in broad terms. This will help the reader understand the way in which the fast jet aircraft is operationally deployed and how it fulfils its mission, along with a greater awareness of the human factors and performance limitations involved. Modern air-to-air missiles are highly capable weapons. Beyond visual range fighting capability became so developed that some aircraft (for example, the F-4 in the 1960s) were not equipped with a cannon or guns. Despite the re-introduction of cannons and guns in fighter aircraft (owing to high casualty rates in Vietnam War among the F-4 community), the dominant weapon for modern air combat remains the air-to-air missile. Air-to-air missiles have a weapon employment zone (WEZ) much larger than that of the gun. WEZ refers to the area around a target aircraft that will result in a high probability of success for a missile fired within that zone. A missile fired outside its WEZ has a low probability of achieving a kill solution. The size of the WEZ varies between different types of air-to-air missiles, depending on the missile’s on-board avionics, propulsion and guidance systems, fuel load and turning ability. The larger the WEZ, the greater the area and number of options that are available to the offensive aircraft for a missile shot. In order to win an air-to-air engagement, the offensive aircraft has only to manoeuvre in such a way that the target aircraft falls into the WEZ for the particular missile that is being carried at the time. This position may not necessarily be directly behind the target. Indeed, with the development of advanced all-aspect air-to-air missiles combining high turning performance with high off-boresight capability, the requirement to position one’s aircraft to the rear of the opponent in order to fire a shot has diminished to a significant extent. Successful shots can now be taken with the opponent aircraft approaching head-on or at off-boresight angles of up to 90°. Air-to-air missiles can be thought of as consisting of three main elements: a guidance system, a warhead, and a propulsion system. Guidance system The guidance system consists of a seeker, designed to identify the target, and an avionics component that guides the missile to the intended target. There are several different types of missile guidance technology, but chief among these are radar and infra-red (IR) guidance. IR guided missiles home on the heat produced by an aircraft, either from the hot exhaust generated by the engines, or in modern systems the friction developed by the passage of the aircraft through the air, leading to a rise in aircraft skin temperatures. While early IR missiles required the pilot to position the aircraft behind the target aircraft, where the heat signature was greatest, the latest IR missiles are able to detect engine exhaust from the side or the front, and at a

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greater distance. These latest IR missiles are said to have all-aspect capability, meaning that the missile’s intercept geometry consists of a wide range of angles relative to the target aircraft. This greater level of sophistication has been combined 20+ Miles

Missile Zone

Gun Zone

High Off-Boresight Missile Zone

Figure 1.1

Weapon Employment Zone

Guidance system

Seeker head

Figure 1.2

Control Fins

Target Detector

Air-to-air missile

Warhead

Rocket motor

Wings

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with infra-red search and track systems, off-boresight capability, helmet-mounted sighting systems, laser rangefinders and enhanced digital signal processing. Radar guidance is normally used for missiles with medium or long range, since the heat signature of the target diminishes with distance. There are three major types of radar-guided missile – active, semi-active, and passive. Active radar (AR)-guided missiles carry their own radar system to detect and track the target, whereas semi-active systems rely on radar energy emitted by the launching aircraft reflecting off the target aircraft. The advantage of the AR-guided missile is that it can function in a so-called ‘fire and forget’ mode, leaving the launching aircraft free to engage other targets. The semi-active missile requires the launching aircraft to lock its radar on the target for the entire duration of the missile’s journey. Other forms of guidance include electro-optical imaging and passive antiradiation guidance. The latter depend on radar emissions from target aircraft, such as other fighters or even airborne early warning and control aircraft. Warhead The warhead is generally a conventional high explosive blast warhead, fragmentation warhead, or continuous rod warhead (or a combination of any of those three warhead types) is typically used in the attempt to disable or destroy the target aircraft. Warheads are typically detonated by a proximity fuse or by an impact fuse if it scores a direct hit. Propulsion system The propulsion system is usually of solid-fuel rocket type. There may be two such rocket motors, with the second one being used in the terminal stages to ensure a successful hit. The control actuation system is typically an electro-mechanical, servo control actuation system, which takes input from the guidance system’s avionics and activates the airfoils or fins at the rear of the missile that steer the weapon to target. Modern high-agility missiles are employing gimballed thrust to help improve launch efficiency and target acquisition. A missile’s effective range is dependent on factors such as altitude, speed, position and direction of the target aircraft as well as those of the attacking aircraft. Furthermore, anti-missile manoeuvres and electronic countermeasures employed by the target aircraft can limit the ability of the missile to hit its intended target. Fighter Tactics The raison d’être of a fighter aircraft is to achieve air superiority. At a certain point, achieving this will require the successful prosecution of air combat against the enemy. Air combat is a highly fluid, highly complex form of warfare. It is dynamic, fast-moving and three-dimensional. For the purposes of understanding the operational environment of the fast jet pilot, it is useful to consider air combat as consisting of three major phases: detection, engagement and disengagement.

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Detection is of vital importance. This underscores the modern air combat principle of ‘first look, first shot, first kill’. This principle has driven the development of increasingly powerful and capable airborne radar systems and airto-air missiles. This has given the modern fighter pilot the ability to identify and destroy airborne targets beyond visual range. Identifying the target, either visually or via on-board systems such as radar, allows the fast jet pilot to prosecute a so-called first-pass kill, where the opponent may be defeated without his being aware, caught entirely by surprise and defeated by employment of an appropriate weapon. This is what happens with beyond visual range kills. Early detection allows the fast jet pilot to enjoy the element of surprise, which affords him many more possibilities. The modern sensor systems that allow for detection of enemy aircraft are discussed in Chapter 6 Are the circumstances favourable for attack? Is it better to not engage? Could it be a trap? Early detection gives a heightened degree of situational awareness (SA). Once the decision has been made to launch an attack on the detected target, the fast jet pilot is then said to have engaged the target. The engagement phase consists of the closing phase, the attack phase and the manoeuvring phase. Depending on the circumstances, all of these elements may occur almost simultaneously. Closing involves reducing the distance to the target aircraft, and getting within appropriate range and in the correct position for the weapon system to be employed. Closing as quickly as possible reduces the chances that the target aircraft will detect the oncoming attack and respond accordingly. High closure rate allows the element of surprise to be maintained for as long as possible. Having closed on the target, the attack is now underway properly. This is often a decisive phase, and depends on the weapons being employed. If performed correctly, the target may literally never know what hit it. With modern air-to-air missiles, the kill solution can be achieved very rapidly, without the need for a lot of manoeuvring against the target. Ideally, the target is defeated at the first pass, often at considerable distance if beyond visual range. However, not all target aircraft will be entirely caught by surprise. On-board radar warning receivers and inbound threat warnings may alert the target aircraft to the looming attack. The engagement may then enter the manoeuvring phase, with the aggressor aircraft unsuccessfully achieving a first-pass kill. The manoeuvre phase is often popularly referred to as the ‘dogfight’ but is more accurately and formally referred to as an air combat manoeuvring (ACM) engagement. In simple terms, the manoeuvring phase involves each aircraft trying to achieve an optimum firing position first. This firing position depends on the weapons load being carried. A firing solution for a guns kill is vastly different from what is required for an all-aspect air-to-air missile. Over the years, the level of sophistication of air combat manoeuvring has increased significantly. Air combat manoeuvring relies on the pilot performing a number of basic fighter manoeuvres (BFM) in order to achieve a winning position in the battle. BFM are taught to all fighter pilots, and are based on years of operational experience. They require a good understanding of flight dynamics and geometry, and an ability on the part of

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the pilot to understand the changing aspect of the engagement geometry in realtime. BFM and ACM can be extremely complex. In general, BFM and ACM all come down to energy management of the aircraft. Energy management of the fast jet is essential for survival, let alone victory. Keeping the energy state of the aircraft high gives maximum manoeuvring capability. It is an axiom of air combat that ‘speed is life’ – allowing the aircraft to get too slow (that is, to be in a low-energy state) presents more opportunities for the opponent to take advantage of. With conventional fast jet aircraft, heavy manoeuvring at high G loads bleeds off airspeed, and the aircraft subsequently approaches its minimum flying speed, Vmin. One way to offset this is to provide more engine thrust, but there is still only a finite amount of thrust available from a given powerplant. Below Vmin, the aircraft stalls owing to lack of effective lift and aerodynamic control. Vmin thus becomes an important limiting factor in manoeuvring flight. Nose-pointing ability, particularly during tracking of the opponent for a guns kill, requires the ability to rapidly pitch the nose up at the target. Such a manoeuvre will generate a high angle of attack (AOA) relative to the aircraft’s velocity vector. AOA is the angle formed between the chord line of the wing and the velocity vector of the aircraft, and is expressed as units or degrees of alpha or AOA. At high AOA, the aircraft’s energy state rapidly decays as airspeed is bled off owing

Structural Damage/Failure Area

+Gz Limit

1 0

–Gz Limit Structural Damage/Failure Area Vmin

Vc Airspeed

Figure 1.3

Generic V-n diagram for a fighter aircraft

Vne

Structural Damage/Failure Area

Lift Limit Limit Speed

Load Factor (Gz)

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9

to drag. The limiting lift speed is approached, and if the manoeuvre is maintained, the aircraft will stall and lose aerodynamic control in all three primary axes. The control surfaces (elevators, ailerons and rudders) become ineffective owing to the presence of low-energy airflow and wake shed from the wings and forward fuselage. Aircraft such as the F/A-18 can generate relatively large AOAs (in the order of 35°) but at the expense of some controllability and agility. During an air combat engagement, entering a stall puts the aircraft at the mercy of the opponent. The aircraft can no longer be manoeuvred into a winning position, and at the same time is unable to disengage and escape from the engagement. It is thus clearly imperative for a fast jet pilot in an air combat engagement to be acutely aware of the aircraft’s energy state (as well as fuel state, since running out of fuel is also going to result in losing the battle). Basic fighter manoeuvres give a fast jet pilot an arsenal of manoeuvres to try against an opponent in order to secure victory. They have been described as the building blocks of fighter tactics. These manoeuvres if performed correctly, will keep the energy state of the aircraft optimised, and reduce the time it takes to achieve the optimum firing position. A complete description of all manoeuvres available to a fast jet pilot is beyond the intended scope of this book. However, it is useful to briefly discuss some basic fighter manoeuvres in order for the reader to have an appreciation of the highly complex, dynamic and three-dimensional nature of fast jet air combat. When closing to engage a target aircraft, especially if it is in turning away from the aggressor, the attacking aircraft can fly a so-called pursuit curve, which is flown relative to the target. Three different curves are described: lead pursuit (where the aircraft’s nose is positioned ahead of the target), pure pursuit (where the aircraft’s nose is positioned on the target), and lag pursuit (where the aircraft’s nose is positioned behind the target). Which one to fly depends on the developing tactical situation. Pure pursuit can be used to present the smallest visual image to the target during closure, in order to maintain the element of surprise for as long as possible. Lead pursuit may be the best option when attempting to rapidly close on the target, or for a close-in guns kill, and lag pursuit may be required when the closure speed is too high and a rear-quarter position relative to the target is desired. The choice is not fixed – indeed, as the air combat situation evolves a switch from one curve to another may be required in order to maintain tactical advantage. It is important to remember the three-dimensional nature of these manoeuvres. Airspeed can be converted to altitude, and vice versa, in order to preserve or increase the energy state of the aircraft. As an example, an attacker closing in lead pursuit to a target aircraft may overshoot, losing all tactical advantage. To counter this, the attacker climbs the aircraft, reducing the closure rate to the target by performing an out-of-geometric-plane manoeuvre. The attacker rolls the aircraft and then descends, converting altitude to airspeed and achieving a lag pursuit outcome more suitable for a firing solution. Throughout this manoeuvre (known as a lag pursuit roll) the attacker has maintained the aircraft’s energy state and kept visual contact with the target. If the target reverses direction during the roll, the

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attacker has several options, such as to continue the roll around the target and end up in lag pursuit on the other side. Following on from this are the yo-yo manoeuvres, which can be either high or low. These involve airspeed-altitude exchange either above (high yo-yo) or below (low yo-yo) the target aircraft. The yo-yo manoeuvre allows the attacker to change the geometry of a stabilised turning engagement hopefully to his advantage. Rather than pulling more G to get into a better horizontal position (which would reduce speed and thus the energy state of the aircraft), the yo-yo manoeuvre allows the aircraft to achieve this with a greater energy state. Out-of-plane manoeuvres such as lag rolls and high and low yo-yos allow the attacker to improve his positional advantage relative to the target, all the while maintaining or improving the energy state. However, it must be remembered that the target may be actively defending against the attacker, and BFM tactics can be employed in a defensive mode (hence the terms offensive and defensive BFM). For example, if the attacker goes into a low yo-yo to try to create a geometric advantage, the target aircraft could counter this by immediately going into a high yo-yo, thus neutralising the attacker’s advantage. The outcome of the engagement may then be a result of who can react fast enough to the moves of the adversary. Here, the role of situational awareness is paramount. While awareness of one’s own energy state is important, being able to correctly interpret the likely energy state of the target aircraft and making the appropriate BFM tactical choice as a result can be the difference between victory and defeat. There are a multitude of other basic fighter manoeuvres, too numerous to discuss in detail. They are all effectively variations on a geometric theme, however. They include the lead turn, the flat scissors, the rolling scissors and the defensive spiral. Altitude-airspeed exchange and three-dimensional positioning relative to the target are all common elements of BFM tactics. 2

2 1 3 1

3

Figure 1.4

High Yo-Yo manoeuvre

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How and when BFM tactics are employed depends on a vast number of variables. The engagement may be between two similar aircraft (a 1 vs 1 similar ACM engagement). This is the most straightforward type of ACM to consider. The situation gets more complicated when the number of aircraft grows. Two vs 1 or 2 vs 2 ACM require different approaches, given the number of aircraft involved. In addition, when the opposing aircraft are of different capability (dissimilar ACM) the issues get complicated further, especially in multiple aircraft engagements. Disengagement is the final phase of air combat, and for a modern fast jet pilot this involves getting outside the weapon employment zone of the opponent, either through speed, turning ability or altitude change (or often all three simultaneously). Employing electronic countermeasures such as weapons jammers and deploying chaff and flares can be used in addition to manoeuvring to effectively disengage from an attack. Knowing when and how to do this at the exact correct time is indeed a fine art. Disengaging from a fight at the wrong time may make the aircraft an easier target for the opponent. Sometimes, of course, disengaging may be the only viable option, particularly in a low-fuel situation or during a non-combat aircraft emergency. Fighter Missions It is useful now to consider the operational employment of fast jet aircraft in the fighter role. The mission may be one of achieving and maintaining air superiority and air dominance, or the specific interception and interdiction of another aircraft (possibly with assistance from ground-based radar). Fighter sweep The fighter sweep is a mission flown over hostile or contested territory, in order to engage and destroy enemy fighters or targets of opportunity. The idea is to establish and maintain air superiority, that is, denial of the use of the airspace by the enemy. There are several ways in which this might be achieved. A formation of fast jets might conduct a dummy strike against a high-value target, such as an airfield or logistics area. The idea here is to reveal one’s presence and flush out enemy fighters. Once the enemy fighters intervene, they then become the real targets. For these missions to be useful and succeed, the area of attack needs to be cleared of any friendly forces, so that any aircraft that enter the area can be assumed to be hostile. The sweep may be conducted using several formations, flying over the target at different times and possibly from different directions and altitudes. Point defence This type of mission is aimed at protecting a fixed asset or ground object from attack by enemy forces. Point defence can involve combat air patrol (CAP) or GCI (ground-controlled intercept). CAP missions are an airborne patrol, where the fast jets fly in a designated area, ready to intercept any inbound enemy aircraft. The

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CAP might involve protecting a mobile high-value asset such as an airborne early warning and control aircraft, or a fixed, ground-based asset such as a headquarters building or communications centre. The aircraft fly a regular pattern around the asset, out to a -predetermined maximum range. It may involve the use of airborne refuelling aircraft (a clear force multiplier), and one jet flying away from the asset as another one flies back (that is, two jets on reciprocal legs of a racetrack pattern). The aim of the CAP might be to destroy incoming enemy fighters, or prevent an enemy mission from succeeding by acting as a deterrent (that is, turning bombers away or forcing them to jettison their bombs early). A GCI mission involves the fighters (airborne or on the ground) being tasked with an immediate requirement to intercept an identified incoming aircraft which is deemed a threat. These missions represent elements of an integrated air defence system, where aircraft assets are matched with detection and surveillance systems such as radar. Strike escort This mission type is aimed at protecting an inbound bomber or strike force. In effect, it is a mobile form of point defence, in that the asset being protected is in flight. It might also involve a fighter sweep ahead of the asset, or even a CAP-style escort approach. Any enemy threats to the strike force package will be engaged by the fast jet escorts, in order to ensure the safe arrival of the strike force at its intended target. These are high-risk missions, with operations in enemy airspace, which is often heavily defended. Intercepts Interception missions involve the fast jets being tasked by either ground-based or airborne radar stations (or other sensor type). The fast jets are vectored by the radar station to an intercept with the enemy aircraft, so that they can be engaged. There are many ways that the intercept can be managed from a tactical perspective, depending on the enemy force characteristics (number, aircraft type, relative position, and so on). A pincer movement can be used (intercepting from the left and right sides of the enemy simultaneously), or a stern quarter conversion (intercepting from off the rear), a trail intercept (approaching from the rear). It is important to note that in many cases all of these mission types can be woven into a single mission package, depending on the circumstances and how the overall mission evolves. Attack Aircraft Operations Definition of an Attack Aircraft While a fighter aircraft’s main role is to destroy another aircraft, the role of the attack aircraft is to engage and destroy targets of military value on the ground.

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So, for the purposes of this book, an attack aircraft can be considered to be any fast jet aircraft involved in air-to-ground operations. Within this broad definition, there are two types of ground attack aircraft. There is the dedicated ground attack aircraft, designed with no other purpose in mind than fulfilling the attack mission. There are a small number of these dedicated ground attack aircraft, such as the A-10 Thunderbolt II and the Sukhoi Su-25 Frogfoot. These aircraft are specifically designed as attack aircraft, and as such are strong and often armoured, and will generally have no fighter capability owing to their low turning ability. They often have multiple redundancy levels in critical aircraft systems such as the flight control system, so as to preserve flying ability after sustaining damage. They may carry air-to-air missiles purely for self-protection. The other type is becoming more prominent, and this is the multi-role combat aircraft (sometimes also described as a strike fighter or a dual role fighter-bomber). Examples include the F-16 Fighting Falcon, the Mirage 2000D, the F-15E Strike Eagle and the F/A-18 Super Hornet, to name a few. Increasingly, lead-in fighter training aircraft are given so-called light attack roles. While traditionally sued for training, these very capable aircraft can be put to front-line use. The air-to-ground ordnance carried is generally less in amount and capability than a more dedicated attack aircraft, reflecting their relatively smaller size and performance envelopes. Examples include the Hawk and AMX aircraft. Weapons Systems The weapons used in air-to-ground missions are as numerous as air-to-air ordnance. They include guns and cannon, rockets, various unguided ‘dumb’ bombs, and precision-guided munitions (‘smart bombs’). Cannons and guns, either the internally fitted version or carried externally (as an underwing or underbelly gun pod for the specific mission), are used for strafing, the laying down of fire against a target. These autocannons are generally either of the revolver type (single-barrel, multiple rotating cylinders) or Gatling type (multiple rotating barrels). For example, the A-10 Thunderbolt II carries a 30 mm GAU-8/A Avenger Gatling-type internal cannon firing armour-piercing depleted uranium rounds. It has a substantial rate of fire, in the order of 3,900 rounds per minute. Rockets tend to be fitted externally in wing-mounted or underbelly mounted pods. The most popular calibre of rocket in use today is 8 mm (2.7 inch). Multiple rockets are carried in each pod, and each rocket consists of a single rocket motor and a warhead. Non-precision (‘dumb’) bombs vary significantly in size and explosive capacity (for example, 500 lb bombs up to 2,000 lbs). The successful use of these weapons depends on the pilot flying an accurate approach to the target, with the subsequent trajectory of the bomb when released carrying it to the target. This requires skill and practice. The general purpose dumb bomb can be converted to a precisionguided munition by adding a JDAM (Joint Direct Attack Munition) kit to the

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bomb. This allows it to be delivered with greater accuracy to the target, through the use of a tail-mounted flight control system, an on-board inertial navigation system (which takes position information from the aircraft when released) and a global positioning system receiver. The range of precision-guided air-to-ground munitions available is large. In general, these weapons (of varying size and capability) are guided to their targets by systems such as laser, infra-red, electro-optical technology, millimetre wave radar, or satellite (GPS-based) information. Satellite guidance does not suffer from problems common to other guidance systems such as reduced accuracy owing to weather-related poor visibility. Attack Missions The attack role involves operations against ground targets, but to a lesser degree than bombing (which can deliver significantly more weapons payload than an attack aircraft, across a wider area and usually for strategic rather than tactical purposes). Attack missions generally involve a different threat environment than air-to-air fighter missions. Attack aircraft operate closer to the ground, and are therefore much more likely to be engaged by defending ground-based forces with small arms fire and anti-aircraft weapons. There are essentially two main types of attack mission. The first is close air support (CAS), where operations are conducted against an enemy force in close proximity to friendly ground troops. Given this close proximity, there is potential for friendly fire incidents. As such, a CAS mission requires good communications and coordination with ground forces. This task is often performed by forward air controllers (FAC), either on the ground with the troops or airborne in the immediate area. Good intelligence and reconnaissance are also crucial to the effective CAS mission. The technological improvement of air-to-ground weapons in terms of accuracy of delivery to the target has also helped with the success of the CAS mission. The second mission type is air interdiction, where operations are conducted against specific ground targets, such as buildings, vehicles, bridges and infrastructure. The fundamental difference between CAS and air interdiction is proximity to friendly ground forces. The air interdiction mission is thus not as dependent on communications and coordination with ground forces. Air interdiction is effectively a pure air-to-ground operation against a specific localised target for military advantage. It might therefore involve attacking a bridge or railway in order to disrupt an enemy supply line, or destroying a ship or enemy aircraft on the ground. A special form of interdiction is the engagement and destruction of enemy anti-aircraft systems, including radar stations, surface-to-air missile systems, and so on. This is known as suppression of enemy air defences (SEAD), and usually involves the aircraft deliberately positioning itself as a target so that the air defences will engage their targeting and tracking systems. The aircraft will then launch an attack against the electronic transmissions using high-speed anti-

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radiation missiles (such as the AGM-88 HARM) in order to destroy the ground station before it has the opportunity to fire a weapon at the aircraft. Needless to say, this is a particularly hazardous form of attack mission. The successful prosecution of the attack mission depends on several factors. Good reliable intelligence is crucial, and this often involves other assets such as satellite-based sensors or airborne warning and control aircraft. Good robust communications and coordination can make or break the mission. Accurate position reporting and battlefield situational awareness (SA) make substantial contributions to the communication and coordination task. One factor that adds complexity to position reporting and battlefield situational awareness is the terrain. For example dense jungle makes attack missions more difficult, owing to problematic visualisation of the target and any friendly forces in proximity, and can also make damage and effectiveness assessment harder. In contrast, open desert terrain has less of these issues at work. However, even in such topography the need for good intelligence, communications and coordination remains essential. Attack Aircraft Tactics Attack aircraft tactics are relatively straightforward, given that the weapon is generally delivered to a fixed target. Cannon and rocket attacks usually require the aircraft to fly a descending profile to the target, with the relevant sighting system fixed on the target directly ahead of the aircraft. The descent angle might be 30°, and the cannon might be fired at a slant range of up to 4,000 feet from the target. Once the firing sequence is completed, the aircraft pulls up away from the ground and the target. Unguided weapons require the aircraft to be positioned at a certain speed, altitude and distance from the target such that after release, gravity and the momentum of the weapon will carry it to the target. This requires some skill on the part of the pilot. The aircraft might enter the target area at low level and high speed, bank hard to one direction to offset the approach by 10°, then pull up at 10° pitch before rolling at a certain altitude into the target, with the bombs released during the subsequent dive when the bomb sight picture is optimal. The aircraft then pulls up and egresses after the bomb is released. The geometry of this bomb delivery technique will vary depending on the weapon and the aircraft. The tactical delivery of precision-guided munitions will depend on the type of weapon used, especially on the guidance system employed. Some weapons might require the aircraft to continually lase the target such that the weapon flies down the laser beam to impact with the target. Other systems will require the aircraft to be flown in a specific manoeuvre (for example, in order to optimise the trajectory of the bomb by ‘tossing’ it from the aircraft and then allowing the guidance and flight control system to maximise the accuracy of the bomb’s glidepath to the target). Satellite guidance systems usually allow the aircraft to effectively ‘fire and forget’ with the weapon’s on-board systems independently ensuring a high level of flight path accuracy to the intended target.

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Super-Agile Flight Future fast jet aircraft are likely to have super-agile flight characteristics as a standard element of their performance envelope. Such super-agile aircraft may be considered to be sixth-generation fighters. These aircraft may also be more fuel efficient, have far greater top-end speed (multi-Mach number), and be highly stealthy, with sophisticated sensor systems and digital information processing capabilities. Matched with equally high-performance advanced weapons, these aircraft would offer unparalleled air dominance to forces using them. Future attack aircraft will need increasing agility to avoid more sophisticated ground-based tracking systems and surface-to-air offensive weapons systems. Similarly, next-generation fighter aircraft will need increased agility to outmanoeuvre opponents in air engagements, either to gain an offensive advantage or defend against an enemy’s all-aspect air-to-air missile. Super-agile flight can be defined as full control authority at high AOA in the post-stall region of the manoeuvring envelope (Newman, 1998; Newman and Ostler, 2011). This is achieved through applying extremely relaxed stability criteria in the design of the aircraft, and the employment of advanced aerodynamic features such as thrust vectoring, canard foreplanes, and advanced digital flight control systems. These all combine to give a greatly expanded operating envelope, with improvements in turn radius, rate of turn, directional change, rate of deceleration, angle of attack, low-speed flight, pitch rate and nose authority. The latter two elements, for example, can allow the aircraft to continuously track the opponent aircraft despite any defensive manoeuvring the latter may employ. In tactical terms, the super-agile aircraft can rapidly achieve a satisfactory firing solution by gaining positional advantage in an air-to-air engagement quicker and more effectively than an opponent. By exploiting its high angle of attack and nose-pointing capabilities, the super-agile aircraft can continuously threaten and intimidate the opponent aircraft. Moreover, conventional clues as to an opponent’s energy state will be denied to the target aircraft, as attitude, aspect, angle of attack and nose position will no longer have the same meaning in a super-agile aircraft. This alone can tip the balance of an engagement in favour of the super-agile aircraft, by momentarily confusing the opponent. From a human factors and performance limitations perspective, these aircraft put the pilot in a more demanding environment by virtue of the super-agile characteristics of the aircraft. The acceleration environment of these aircraft is very complex, as it will not be limited to excursions in the Gz axis, but also in the Gx and Gy axes (front-to-back and lateral axes, respectively). This will have implications for human tolerance, such as the ability to withstand the sudden multiaxis G applications, the added complexity of achieving a successful ejection, and the potential for spatial disorientation of the fast jet aircrew. As the following chapters show, these problems are still challenges for today’s fast jet aircrew, let alone those in the future.

Chapter 2

Altitude The modern fast jet is capable of flight at altitudes well in excess of 40,000 ft. While this is advantageous from the point of view of aerodynamic performance and engine efficiency, this high altitude poses a number of physiological and performance risks for the crew if the altitude protection systems fail. This chapter will look at the challenges involved in operating fast jet aircraft in a low-pressure, low-oxygen environment. While all aircraft are exposed to the potentially adverse effects of altitude, the fast jet’s performance envelope means that it can undergo very rapid altitude change. The low-pressure environment can cause a number of problems for aircrew, such as ear and sinus barotrauma. The problem of hypoxia owing to the low oxygen content of the atmosphere at altitude is a very serious issue. Hypoxia can lead to various symptoms ranging from impaired performance through to loss of consciousness and death. In order to protect the fast jet crew from the hazards of the low-pressure, low-oxygen environment, various sophisticated safety systems have been developed, which are now quite mature from a technological perspective. These consist mainly of a cockpit pressurisation system and a personal breathing system, both of which will be considered in some detail. Finally, two uncommon but potentially significant altitude-related problems (decompression illness and ebullism) will be discussed. Atmospheric Physics The low-pressure, low-oxygen environment of the fast jet at altitude is a basic function of the fundamental composition of the Earth’s atmosphere, which behaves in predictable and well-documented ways. The air in the atmosphere is composed (in simple terms) of 21 per cent oxygen, 78 per cent nitrogen and the remaining 1 per cent is made up of a combination of miscellaneous and rare gases (argon, xenon, and so on). Up to an altitude of approximately 300,000 ft, the proportion of oxygen in the atmosphere remains constant at a level of 21 per cent. As altitude increases, the total atmospheric pressure decreases in an exponential manner. At 18,000 ft, ambient atmospheric pressure is half that of sea-level, and at 33,700 ft ambient pressure is one-quarter that of sea-level. At 100,000 ft, ambient pressure is only 1 per cent of sea-level. Thus, half of the sea-level atmospheric pressure is lost by ascent to 18,000 ft, but the other half takes much longer to lose (travel to the outermost reaches of the atmosphere is required). This total atmospheric pressure reduction therefore results in a decrease in the partial pressures of each of the constituent gases of the air (in accordance with Dalton’s Law). So, at altitude,

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while there will be fewer total molecules of gas per unit volume, 21 per cent of those molecules will still be oxygen. However, at high altitudes there may be insufficient molecules of oxygen available to satisfy the body’s basic demand, leading to the onset of the signs and symptoms of hypoxia. The decline in atmospheric pressure with increasing altitude can lead to a number of physiological effects (see next section). These physiological effects occur as a function of Boyle’s Law, which states that pressure and volume are inversely related (assuming temperature remains constant). From a physiological point of view, Boyle’s Law means that any trapped gas in the body will expand with increasing altitude. Low Pressure The operating environment of fast jet pilots (as seen in the previous chapter) is dynamic and challenging, and involves the capability for rapid altitude change. As such, the fast jet environment generates the most significant barometric changes (Larsen et al., 2003). There are several gas-containing areas of the human body that are affected by these altitude-related pressure changes. These include the teeth, the lungs, the gastrointestinal tract, the middle ear and the sinuses. Any gas in these areas will expand and contract in inverse relation to pressure changes in accordance with Boyle’s Law. Air trapped in and around the teeth may be due to poor dental hygiene, abscess formation or poorly filled cavities. Any gas in such situations may react to the pressure change, and cause pain. This is known as barodontalgia, and has been well documented in military aircrew. In an Israeli study, at least one case of barodontalgia was reported in 8.2 per cent of respondents, with the highest number of incidents reported in fighter pilots (Zadik et al., 2007). The lungs, under normal conditions, contain up to six litres of air. As altitude increases, the expanding air will simply exit the lungs through the nose and mouth, without the pilot being aware of it. Even with sudden and dramatic pressure changes, the outflow of significant amounts of air from the lungs is rapid and generally not noticed by the individual. However, if the normal exits are not available (i.e., the mouth is closed and the nose blocked), the expanding air will force its way out of the lungs in accordance with the pressure differential. Generally this will cause significant problems, with either a tear in the lung tissue itself leading to air collecting outside the lung but within the chest cavity (a pneumothorax). This can lead to significant respiratory distress, loss of consciousness and death if not treated promptly. Similarly, expanding gas escaping through damaged lung tissue can enter the blood stream and lead to embolic phenomena and stroke. Pneumomediastinum is the term given to the situation where gas is collecting in the central part of the chest between and outside the lungs. This can put significant pressure on the heart, leading to arrhythmias and disturbed function, as well as chest pain and respiratory difficulties.

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19

Boyle’s Law will also result in gas within the gastrointestinal tract expanding with increasing altitude. This expanding gas, if unable to be vented, can cause significant pain and in some cases can result in collapse. This is most likely due to a gas bubble in the small intestine not being able to move to where it can be vented to the outside world, and simply expanding in place and putting considerable strain on the intestinal wall. Ear and sinus pain associated with altitude are common problems in aviation medicine. Such pain is known as barotrauma (Campbell, 1944; Gargas, 1985; Parris and Frenkiel, 1995; Parsons et al., 1997). Air contained in the middle ear and sinuses will vent naturally during ascent. During descent, it is more difficult (owing to the anatomical nature of the Eustachian tube and the sinuses) for air to re-enter these spaces, particularly the middle ear. As such, barotrauma often tends to be more of a problem during descent (especially an emergency, high-rate descent). The increasing difference in air pressure across the eardrum with descent can cause significant pain. These problems will be more likely to occur (and will be symptomatically worse if they do) if the pilot has a cold, since the inflamed and swollen mucosal membranes make re-equilibration of the air pressures more difficult. In some cases, one ear might equalise the pressure across the eardrum while the other may not, leading to a situation known as alternobaric or pressure vertigo with sudden onset of dizziness. This can be disabling and disorienting, and in severe situations it can even be incapacitating. The Valsalva manoeuvre involves a forced expiration with the nose and mouth closed. This technique forces air up the Eustachian tube and overpressurises the middle ear, allowing the pressures across the eardrum to be equalised. This manoeuvre needs to be performed frequently during descent to prevent barotrauma symptoms from occurring. It is important to note that even in a pressurised cockpit (see later) there is a need to equalise the ear pressures on descent, even though the magnitude of the pressure change is less than that occurring outside the aircraft. Barotrauma can still occur on a descent from 20,000 cockpit altitude to groundlevel if ear pressures are not equalised during the descent. The challenge for a fast jet pilot is that pinching off the nostrils to ensure air cannot escape from the nose during the Valsalva manoeuvre is not easy owing to the wearing of an oxygen mask. In effect, there are two ways that this can be overcome. In some masks, it is possible to force the fingers in between the hard exoskeleton of the mask and the inner soft rubber part attached to the face. In doing so, it is possible to pinch the nostrils shut while still wearing the mask. In many ways, it is easier to do what many fast jet pilots learn quickly to do – simply block off the exhaust outlet of the mask by putting a hand over it and forcefully exhaling in to the mask. With the exhaust outlet blocked, the high-pressure air will force its way up the Eustachian tube. With practice, the Valsalva manoeuvre can be done quickly and repetitively with this technique. It is important to be able to do a Valsalva with the mask on, as removing it not only interferes with communication but also potentially increases the risk of hypoxia.

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Hypoxia Hypoxia is defined as an inadequate supply of oxygen to the tissues of the body sufficient to cause impairment of function. It has been said that hypoxia is the most serious single hazard during flight at altitude (Ernsting, 1984). Hypoxia becomes more likely as altitude increases. From a physiological point of view, altitude does not pose too many problems for the average fit and healthy human until 10,000 ft is reached. Beyond this altitude, the oxygen saturation (or content) of the blood’s haemoglobin begins to deteriorate. The 10,000 foot altitude level coincides with that point on the oxygen-haemoglobin dissociation curve at which progressively severe desaturation begins to occur. This is demonstrated in Figure 2.1. The desaturation effect becomes more severe with altitudes beyond 10,000 ft. In the absence of an adequate oxygen supply beyond 10,000 ft, hypoxia is said to occur. The hypoxia-induced impairment of function affects most body organs and activities, and is most pronounced in terms of mental and cognitive function. Loss of consciousness followed by death will occur if hypoxia continues. Pilots suffering from the insidious effects of hypoxia are the poorest judges of the impact on their flying performance. Any strange or unusual symptoms at altitude should be considered to be due to hypoxia first and foremost, since it is the most dangerous, time-limited problem. Hypoxia makes even the simplest tasks more difficult at altitude. As such, hypoxia remains an ever-present, insidious threat to the safety of any fast jet mission. It is a risk that should never be taken lightly. 10,000 ft

100

5,000 ft

90

% Haemoglobin saturation

80 70 60 50 40 30 20 10 0

0

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30

40

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Alveolar PO2 (mm Hg)

Figure 2.1

Oxygen-haemoglobin dissociation curve

80

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Incidence A United States Air Force study examined hypoxia incidents occurring between 1976 and 1990. In this time, there were 656 incidents (Island and Fraley, 1993). The vast majority of these incidents occurred in aircrew who had undergone altitude chamber training, and only 4 per cent of these suffered loss of consciousness. In contrast, 94 per cent of individuals who had not had prior altitude exposure training suffered loss of consciousness. Almost all of the aircrew who had received prior altitude training in a hypobaric chamber were able to recognise their own particular signs and symptoms, and thus take appropriate corrective action. This highlights the importance and effectiveness of ground-based altitude and hypoxia awareness training. In a USAF study of 298 in-flight hypoxia events, 48 (16 per cent) occurred in fighter aircraft (Rayman and McNaughton, 1983). The symptoms reported were of a mild hypoxia nature, including light-headedness, visual changes and impaired cognition. The potential for these symptoms to cause impaired flight performance is clear. The study showed that the cause of the hypoxia problem was due to personal oxygen system failure in 45 per cent of cases. Nineteen per cent were due to loss of cabin pressure, and only 3 per cent of cases were due to removal of the oxygen mask in flight by the crew. A Royal Australian Air Force (RAAF) study for the period 1990 to 2001 showed 27 hypoxia cases involving 29 aircrew (Cable, 2003). There was only one fatality, involving the pilot of an F/A-18 Hornet (see case study). In this study, seven cases of in-flight hypoxia occurred in fast jet aircraft (five in F/A-18 aircraft, two in Macchi MB326H lead-in fighter trainer aircraft). The fast jet aircraft thus contributed some 85 per cent of in-flight hypoxia events in the period under study, with 100 per cent of the fatalities. In terms of the cause of the event, problems with the oxygen system (including mask leakage, regulator failure and connection problems) accounted for 63 per cent of events. A US Navy study of 566 fast jet aviators found an in-flight hypoxia event rate of 20 per cent (Deussing et al., 2011). The majority of these occurred in the F/A-18 aircraft (40 per cent). In 57 per cent of hypoxia cases, the aircrew were not wearing their oxygen masks at the time, in contravention of Navy regulations, which require the mask to be worn at all times during flight. Both Cable (2003) and Rayman and McNaughton (1983) found that in-flight hypoxia is most likely to occur in fast jet aircraft in which an oxygen mask is worn and oxygen breathed via a regulator at all times. Hypoxia symptoms thus occur while already using oxygen equipment. This is a crucial point, and highlights the need for fast jet aircrew to be acutely aware of pressure changes and their own symptoms of hypoxia. In such cases the wearing of an oxygen system can give the crew a false sense of security that they are protected from hypoxia. However, as the evidence shows they are more likely than other crew to suffer from it in-flight, and in most cases the cause is due to a failure of some element of the oxygen delivery system. Indeed, the crucial role that equipment failure plays in cases of

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in-flight hypoxia reinforces the need for regular equipment testing and pre-flight checks, as well as accurate and proper fitting of life support equipment such as the oxygen mask. The cognitive impairment caused by in-flight hypoxia is a particular human factors challenge in that it makes deliberate recognition of the symptoms and accurate processing of that information more problematic for the affected fast jet crewmember. Recognition of symptoms is crucial. Cable (2003) documented the case of a RAAF F/A-18 pilot who experienced symptoms consistent with hyperventilation, correctly assumed that this was due to early onset hypoxia, and took appropriate corrective action. The aircraft had alerted him to an ‘OXY LOW caution’ (which is triggered at a liquid oxygen level of less than 1 litre) at a cockpit altitude of 8,500 ft. Signs and Symptoms An altitude of 10,000 ft is regarded as the critical altitude threshold for the onset of hypoxia. Without supplemental oxygen, a number of well-recognised hypoxia signs and symptoms occur in individuals exposed to altitudes above 10,000 ft. In general, hypoxia is associated with a slow and progressive decline in performance (mental and physical). This is sometimes accompanied with a sense of euphoria. The reduced oxygen saturation of the blood is detected quite early by the chemoreceptors, and a well-documented hypoxic ventilatory response (HVR) is triggered, leading to hyperventilation (which is an attempt to compensate for the low oxygen content by increasing both the rate and depth of respiration). While hypoxia causes impairment of function of just about every organ system, the brain is particularly sensitive to low oxygen levels. Although it accounts for only 2 per cent of body weight, the brain consumes approximately 20 per cent of the entire oxygen uptake. Symptoms of cognitive dysfunction therefore occur after only a relatively short time. These include drowsiness, impaired judgement, poor short-term memory and reduced alertness. Normally straightforward tasks become increasingly difficult. Reasoning skills and decision-making ability are compromised, and information processing and psychomotor abilities are all similarly impaired. Headache is a typical after-effect of hypoxia, as are fatigue and lethargy. The special senses are also susceptible to low oxygen levels. Hearing ability becomes less accurate. Similarly, hypoxia quickly and significantly affects visual ability (Fowler et al., 1993). The light-sensitive elements of the retina (the cone and rod photoreceptors) are particularly affected by low oxygen levels (Connolly and Hosking, 2006; Connolly et al., 2008). Contrast sensitivity, dark adaptation and visual acuity are all impaired. Vision can therefore be affected at relatively low altitudes, especially at night. Visual acuity is reduced by 10 per cent at 5,000 ft, and by 28 per cent at 10,000 ft. In addition, low oxygen levels can affect peripheral vision, producing a tunnel-vision effect.

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Other signs and symptoms include muscle tremors, a blue colouring in the extremities (known as cyanosis). Eventually the situation deteriorates to the point where the pilot becomes semi-conscious, then unconscious. After approximately five minutes without adequate oxygen, death will occur. Well before unconsciousness occurs, the symptoms of hypoxia can clearly impact upon a pilot’s ability to safely operate the aircraft. Indeed, the deterioration in hearing and visual ability, coupled with impaired information processing, makes the detection and recognition of the underlying issue more problematic. While the aircraft may try to warn of a loss of cockpit pressure, with a warning light illuminating, an aural tone or a voice alert, the impaired cognitive state of the pilots may reduce their chances of responding appropriately. The higher the altitude reached, the more marked the features of hypoxia. Rapid rates of ascent can allow high altitudes to be reached before the typical signs and symptoms of hypoxia occur. Unconsciousness may occur first, well before any of the well-described features of hypoxia. With slow onset (and for the purposes of ease of description), four stages of hypoxia have been described: Indifferent, Compensatory, Disturbance and Critical. The Indifferent stage occurs from sea-level up to 10,000 ft. Any performance impairment at altitudes up to 10,000 ft is quite subtle, and may not be readily appreciated by the crew. The Compensatory stage of hypoxia occurs at an altitude range of 10,000–15,000 ft. In this altitude range, the HVR leads to an increase in respiratory rate and depth, and various cognitive impairments are seen. These include drowsiness, decreased judgement, decreased memory, decreased alertness and difficulty executing discrete motor movements. Increased arithmetic errors have been seen after one hour at approximately 12,000 ft (Wu et al., 1998). There is also a reduction in the ability to carry out physical tasks. The Disturbance stage of hypoxia occurs at an altitude range of 15,000– 20,000 ft. In this stage, the symptoms of hypoxia are more pronounced, since the physiological compensatory mechanisms (such as HVR) are no longer adequate. Symptoms and signs can include a feeling of ‘air hunger’ (shortness of breath), cyanosis, euphoria, fatigue, dizziness, headache and sleepiness. Worsening intellectual and cognitive impairment is seen, such as slowed mentation, poor memory, and critical judgement failure. The hypoxia-induced problems with vision are seen in this stage. Auditory acuity and three-dimensional localisation ability are also seen in this stage. The visual and hearing impairment can have an adverse effect on identification and response to warning systems (McAnally et al., 2003). Significant psychomotor problems are also seen in this stage, with loss of fine touch ability and a fine tremor of the hands. The Critical stage occurs at altitudes above 20,000 ft. In this stage, the problems are serious and quickly deteriorating. Mental performance is grossly affected, with confusion and dizziness very pronounced. Task fixation occurs, and reaction times are prolonged. Total incapacitation with loss of consciousness is often rapid in this stage, with little or no warning.

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There is overlap between these stages in terms of when the various signs and symptoms might occur. They are also of course a function of rate of change of altitude. In general, the cognitive impairment effects are quite predictable at altitudes above 15,000 ft, but they are less predictable at lower altitudes, such as 8,000 to 10,000 ft (Petrassi et al., 2012). Tolerance to Hypoxia Tolerance to hypoxia is a multi-factorial phenomenon. Various risk factors can increase the likelihood of hypoxic symptoms occurring on a given day. These include time spent at altitude, physical activity, fatigue, stress, illness, alcohol intake, dehydration, fitness, and of course whether a pilot smokes or not. Such factors can all increase the likelihood of hypoxia, and reduce a pilot’s ability to not only tolerate it but also to accurately detect, recognise and respond to the hypoxic situation. Fitness also plays a role. The aerobically fit person (i.e., someone who runs, cycles or swims regularly) will be relatively more tolerant of hypoxia than a person without the same degree of aerobic fitness. This is because aerobic fitness translates into more efficient use of an available oxygen supply. If that supply is limited (as occurs at altitude) the aerobically fit person will be more tolerant of it (all other things being equal) than someone who is unfit or a smoker (or both). Smoking is an important risk factor for hypoxia, and increases a pilot’s susceptibility to it. Smoking produces carbon monoxide, which binds several hundred times more strongly to haemoglobin than does oxygen. This interferes with the blood’s oxygen carrying capacity, leading to an anaemic form of hypoxia. This carbon monoxide-induced hypoxic effect can persist for some time after exposure to tobacco smoke. Indeed, it is often said that a smoker lives at a physiological altitude some 5,000 ft higher than a non-smoker, all things being equal. However, it must be remembered that tolerance to hypoxia is very much the result of a large degree of individual variation (Petrassi, 2012; Vaernes et al., 1984). This makes it extremely difficult to accurately predict who will tolerate hypoxia more or the altitude at which the signs and symptoms of hypoxia will appear in a given individual. Indeed, there is an emerging body of research that suggests that operationally significant signs and symptoms may occur below 10,000 ft (Smith, 2005). A study involving in-flight monitoring of oxygen saturation found that some people desaturate at moderate altitudes much more dramatically than others (Cottrell et al., 1995). This subgroup of the population may therefore be at greater risk of hypoxia during aircraft flight than others. Other studies suggest that physiological changes can be measured in the pulmonary circulation at altitudes of around 8,000 ft that may be problematic for certain individuals in-flight (Smith et al., 2012). Low-level hypoxic symptomatology is an issue that remains to be investigated further. However, fast jet aircrew should never underestimate the potential effects of hypoxia at even relatively modest altitudes.

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Time of Useful Consciousness The time course of these changes in cognitive and physical function varies with altitude – the higher the altitude, the quicker these impairments occur and the less time the pilot has available for corrective action before he or she is totally incapacitated. The time of useful consciousness (TUC) or effective performance time (EPT) refer to the time between development of an oxygen problem and the point at which a pilot can no longer take effective corrective action. The times are based on controlled experimental altitude exposures in atmospheric chambers, with resting subjects. Generally these times shorten with actual flight owing to other factors such as cold, physical activity, aircraft decompression, illness, individual variation and so on. At 18,000 ft, the TUC is about 20 to 30 minutes, decreasing to about 10 seconds above 40,000 ft. Training Awareness training is all important. It is only by experiencing their own signs and symptoms of hypoxia that pilots become better equipped to recognise it if it should occur to them during flight. Oxygen will only protect the pilot for so long at high altitude, without the additional benefit of either a pressurised cockpit, pressurised breathing air or pressure suit. Recognition of the symptoms of hypoxia, as well as maintaining a heightened sense of awareness of the physical feelings at altitude, as well as a low threshold for suspecting hypoxia and taking corrective actions is very important. This is especially true of high-altitude flights. This issue of altitude awareness and hypoxia training is discussed in more detail in Chapter 8. Cockpit Pressurisation To avoid the physiological limitations of human exposure to altitude, the fast jet cockpit is pressurised to a lower altitude than the aircraft might be operating at. This allows the aircraft to operate at aerodynamically more efficient altitudes while maintaining the occupants of the aircraft at a lower, more physiologically appropriate and tolerable altitude (Ernsting, 1978). In combination with a personal oxygen breathing system, the cockpit pressurisation system prevents the fast jet crew from being exposed to the risks of hypoxia. The pressurisation system also allows the cockpit to be ventilated and maintained at a desired optimal temperature. There are two major classes of cockpit or cabin pressurisation systems: highand low-differential systems. The terms ‘high’ and ‘low’ refer to the maximum differential pressure achieved by the system. Differential pressure relates to the difference between the cockpit pressure and the ambient atmospheric pressure at the altitude at which the aircraft is operating. While a sea-level cockpit pressure might be seen perhaps as most ideal for humans, it is not the best option for the

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economical and efficient use of the aircraft. A sea-level cockpit will generally restrict most aircraft from climbing to their preferred cruise altitude, since the cockpit has a maximum differential pressure. While this maximum value varies with aircraft type and design, for each aircraft this value represents a structural limitation. Thus, the higher the aircraft flies, the higher the cockpit or cabin altitude correspondingly becomes. In addition, more fuel is consumed when the aircraft cockpit is at sea-level pressure, owing to the pressurisation demands as well as the fact that the aircraft is operating at a lower than optimal altitude. Low-differential systems are common in military combat aircraft, such as fast jets. These aircraft tend to have a maximum differential pressure of around 5 per square inch (psi). Passenger-carrying aircraft involved in commercial transport operations almost exclusively have high differential systems (Aerospace Medical Association, 2008; Cottrell, 1988), where the maximum differential pressure is approximately 8.5 psi. The Fast Jet Pressurisation System The environmental conditioning system (ECS) is responsible for pressurisation and conditioning of the air supplied to the cockpit. The ECS draws air from the compressor stage of each engine via the bleed air system. This gives the aircraft access to a pressurised air source, which it uses not only for pressurising the cockpit but also for a variety of other ancillary uses requiring a source of pressurised air. These include anti-G suit inflation, an air source for the on-board oxygen generation systems (OBOGS), throttle boost, window anti-fog and demist, and fuel tank pressurisation. The conditioned air also plays an important role in cooling the cockpit avionics, so as to keep them at optimum operating temperature. The high-pressure bleed air passes through primary and secondary pressure regulators to reduce the pressure, as well as a heat exchanger to reduce the highpressure-related temperatures. Function of the ECS system is generally automatic, but there are some control options for the crew. The controls for the cockpit air conditioning and pressurisation system are located on the ECS panel in the cockpit, which is usually located in a secondary position at the lower part of the instrument panel or on one of the side cockpit consoles. The pilot has only a limited range of controls available. Pressurisation can be selected to Normal (where the system functions purely in an automatic mode), Dump (cockpit unpressurised) and Ram Dump (pressurisation system closed off and cockpit pressure dumped). Bleed air source selection is also available on the ECS panel (depending on the aircraft, to select bleed air from left, right or both engines, or to shut the bleed air system down completely). A temperature control system is also part of the ECS, giving the pilot some limited control over the cockpit air temperature. Failure of the cockpit pressurisation system can represent a serious emergency (see next section). Such failure is indicated to the crew in a number of ways, depending on the aircraft type. Such indications generally take the form of visual and/or aural warnings and cautions, such as warning lights or audible alarms. In the F/A-18 Hornet, the cockpit pressurisation warning system will alert the pilot to

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a cockpit altitude above 21,000 ft. There is also a bleed air leak detection system to alert the pilot to a problem with the bleed air system, since this might result in problems maintaining adequate cockpit pressurisation. In the F/A-18, there is an accompanying voice alert to signal a problem with the bleed air system. It is important to note that in certain circumstances warnings may be triggered at high altitude despite the system working correctly. For example, at an ambient altitude in excess of 47,000 ft, the maximum differential pressure limitation will result in a cockpit altitude in excess of 21,000 ft, triggering a cockpit pressurisation caution light. Cockpit Pressurisation Failure Failure of the cockpit pressurisation system can be due to a variety of causes. Structural failure of the cockpit (owing to combat-related damage or loss of the canopy), engine failure, or some defect in the pressurisation system itself can all lead to failure to maintain cockpit pressurisation. Depressurisation of the cockpit exposes the fast jet crew to an adverse environment that the pressurisation system had been protecting them from. They will be exposed to the risks of hypoxia, barotrauma, decompression illness and even hypothermia. Physiologically, cockpit decompression will cause predictable problems for occupants of an aircraft. There will be a pressure change (especially with the consequent emergency descent). This pressure change will affect the lungs, ears, sinuses and gastrointestinal tract. Hypoxia will be a risk, but generally mitigated by the emergency descent into more oxygen-rich air and the use of 100 per cent oxygen. Normally, the low-differential pressurisation system of military fast jet aircraft should keep the occupant at a cockpit altitude of more or less 18,000 to 20,000 ft while the aircraft actual altitude is 35,000 ft and above. Pressurisation system failure exposes the occupant to a high ambient altitude. At altitudes above 40,000 ft while breathing 100 per cent oxygen, the pilot is physiologically equivalent to being somewhere between 10,000 and 15,000 ft on normal air, since the partial pressures of oxygen in the lung are about the same. The rate of cockpit depressurisation is an important consideration. Under slow rates of pressure loss, the pilot needs to recognise the effects of pressure change or the onset of familiar training-induced signs and symptoms of hypoxia. With rapid decompression, the rate of pressure change can be severe enough to cause unconsciousness as a first response. Even if loss of consciousness does not occur, the pressure change can be severe enough to adversely impact on cognition and interfere with the crew’s ability to respond effectively to the deteriorating situation. While hypobaric chamber studies show that the time of useful consciousness for an individual at 25,000 ft without supplemental oxygen is in the order of 3 to 5 minutes, this time is considerably reduced when the cockpit is rapidly decompressed. Some studies have shown that it can take up to 15 seconds for a military transport aircraft flight crew to don their oxygen masks (George, 1999). In the fast

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Flying Fast Jets

jet environment, the crews are wearing their oxygen masks as a matter of routine, which is clearly protective. However, they must still be aware of pressure changes and hypoxia onset in case their oxygen system is defective. Recognition of hypoxia signs and symptoms, and loss of cockpit pressure, is important such that the crew can take correct and decisive action, such as immediately descending the aircraft to a lower altitude and selecting emergency pressure on their oxygen regulator. How common is loss of cockpit pressurisation in fast jet aircraft? In a US military study covering the years 1981–2003, approximately 43 per cent of cockpit pressurisation loss occurred in fighter and attack aircraft (Files et al., 2005). If fast jet aircraft employed in a training role (such as the T-38 Talon) are included, then the fast jet depressurisation rate in this study increases to 68 per cent (720 out of 1055 incidents). Indeed, in this study the T-38 aircraft had the largest number of depressurisation incidents out of the total. The F-15 and F-16 aircraft accounted for more than half of the fighter/attack depressurisation events. In the fighter/attack category (excluding the T-38 trainer) the most common rate of depressurisation was slow. In a third of the 1,055 depressurisation events, the aircrew involved experienced symptoms of hypoxia, decompression illness or barotrauma (or some combination). Hypoxia was the most common symptom of these (Files et al., 2005). In the RAAF, there were 82 decompressions of military aircraft per million flying hours in the years 1988–2003 (Cable, 2004). Of these, the study showed that fast jet aircraft were statistically more likely to suffer a rapid depressurisation event than a slow one. A Canadian study involving ejection-seat equipped aircraft reported 47 incidents of cockpit depressurisation, with approximately 62 per cent of these being of rapid rate (Brooks, 1984). There were three cases of hypoxia in these events. Loss of cockpit pressurisation is not a common event in fast jet operations, on an event per million flying hours’ basis. When it does occur, in the vast majority of cases the failure to maintain pressurisation is recognised by the crew and appropriate actions taken. While symptoms may occur, they tend to help the crew recognise the problem rather than lead to loss of life. Fatalities owing to cockpit depressurisation in fast jet operations are, thankfully, quite uncommon. Those that do occur, however, are generally considered to be preventable (Files et al., 2005). The Oxygen System It is now worth discussing the oxygen system in the fast jet cockpit. This can be supplied in several forms, either as gaseous oxygen, liquid oxygen or through an on-board generation system. In aircraft such as the F/A-18, the oxygen is supplied in liquid form. A 10-litre supply of liquid oxygen (LOX) is installed in the aircraft. This is a relatively efficient way to carry breathing oxygen – when it vapourises, 1 litre of liquid oxygen is converted into over 800 litres of breathable oxygen. This is likely to last (under normal conditions) well beyond the fuel load of the aircraft. Of course, the rate of breathing of the pilot will determine how long this oxygen supply lasts

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for. In high-workload, stressful situations such as ACM, the fast jet pilot will breathe significantly harder, thus using up the available oxygen much faster. However, high manoeuvring loads will rapidly deplete the aircraft’s fuel load as well. Gaseous oxygen is usually reserved for the emergency supply available to the pilot after ejection from the aircraft (see Chapter 7). This supply is usually only of short duration, in order to give the pilot sufficient oxygen to breathe during the seat-based descent to 10,000 ft. The usual duration is in the range of 10–20 minutes (depending on breathing rate of the pilot). Some modern fast jet aircraft (such as the Eurofighter and F-22) make use of an OBOGS. This system is based on molecular sieve technology. This involves passing engine bleed air (filtered for contaminants first) through a series of specially formulated beds of zeolite crystals (aluminosilicate compounds), which act as molecular sieves and trap molecules such as nitrogen. The end result of this process is a breathable gas consisting of 95 per cent oxygen (with the balance being inert gas such as argon, which has no known physiological effects). The trapped gases (concentrated nitrogen and other gases) are dumped overboard. Some of the generated oxygen is used to back flow through the molecular beds in order to help washout and dump the trapped molecules of non-usable air. This is necessary as the beds of zeolite eventually become saturated with nitrogen and lose their gastrapping ability. In modern OBOGS systems, a solid-state oxygen sensor controls the zeolite bed cycle times for the system, switching between the beds when the oxygen output falls below a predetermined level. There is a gaseous emergency oxygen back-up supply for use in the event of OBOGS failure, decompression, engine failure or ejection. At 25,000 ft, the minimum acceptable oxygen concentration is 63 per cent, with a maximum of 80 per cent, while at 33,000 ft the minimum is 95 per cent and the maximum 100 per cent. One hundred per cent oxygen is therefore only needed above an altitude of 33,000 ft. At ambient altitudes above 40,000 ft (as might occur if cockpit pressurisation is lost), protection from hypoxia is given by 100 per cent oxygen supplied at a positive pressure (up to 30 mmHg pressure). At such high altitudes, 40,000 ft on 100 per cent oxygen is physiologically equivalent to being at 10,000 ft on normal air i.e., on the threshold of hypoxia). Long duration use of oxygen (over several hours) can lead to ‘oxygen ear’. This is a condition in which the oxygen in the middle ear is rapidly absorbed, leading to a relative negative pressure in the middle ear cavity. This causes barotrauma-like pain. Similarly, use of 100 per cent oxygen can lead to collapse of the air sacs in the lower part of the lung, when high +Gz is applied and a G suit is active. This condition is known as ‘acceleration atelectasis’ and is discussed further in Chapter 3. In general, oxygen is an irritant gas, especially after 12 to16 hours of continuous use. At the pilot end of the system, a demand flow breathing regulator reduces the supplied pressure to a normal breathing pressure level. For emergency purposes, the breathing pressure is supplied at a slight positive pressure. This also helps to seal the mask around the pilot’s face (see Chapter 5). There are three basic types of regulator: a panel-mounted regulator (equipped with appropriate

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controls), a chest-mounted regulator attached to the pilot, and an ejection-seatmounted regulator. This last option is the standard system in the Eurofighter and F-35. In the Eurofighter, an Aircrew Services Package (ASP) houses in a single seat-mounted unit a duplex breathing regulator, the anti-G valve system and the personal equipment connector. Other Altitude Problems These tend to be relatively less commonly seen than hypoxia and pressure problems, but they are potentially serious and therefore for the purposes of completeness they warrant a brief mention here. Decompression Illness Decompression illness is a so-called evolved gas disorder, owing to the presence of nitrogen in cells of the body (which tend to be supersaturated). DCI causes a number of well-known syndromes, such as the bends (joint pain) and chokes (respiratory symptoms such as shortness of breath, cough and pain), among others (Pilmanis, 1996). The basic underlying mechanism of DCI is based on Henry’s Law (which states that the amount of gas held in solution is proportional to the pressure of the gas above the solution), and also Haldane’s critical saturation ratio (2:1). A reduction in ambient pressure owing to increasing altitude (especially if rapid) will lead to nitrogen bubbles forming in the blood and cells, which can travel to any other part of the body triggering direct physical and indirect immunological responses. The theoretical threshold for DCI is 18,000 ft (half sea-level atmospheric pressure, thus satisfying Haldane’s ratio), but in clinical terms the practical threshold is more like 25,000 ft, where the incidence of DCI climbs significantly (owing to the bubbles now being of clinically relevant size and number). The 18,000 ft threshold for DCI in a sea-level acclimatised person has been documented in several studies, but there have also been reports of DCI occurring at lower altitudes, around 15,000 ft (Haske, 2002; Webb et al., 1998; Webb et al., 2003) and even at 11,000 ft following prolonged exposure to altitude with additional risk factors such as exercise (Kumar et al., 1990). In accordance with Boyle’s Law, any bubbles formed will vary in size inversely with pressure (i.e., ambient altitude). This important gas law underpins the fundamental treatment for DCI – recompression therapy. In aviation, DCI occurs at altitude, and is therapeutically benefited by a descent and landing. In most cases this will lead to cessation of symptoms and an apparent (sometimes actual) cure. However, monitoring for the subsequent 24-hour period needs to be done, owing to the potential for DCI issues to remain (owing to the immunological responses mounted by the body in response to the presence of bubbles, which can lead in worst cases to secondary circulatory collapse). The basic emergency actions to be carried out by the pilot suspecting DCI are an immediate descent, use of 100 per

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cent oxygen, staying warm and minimising physical activity. Medical help needs to be sought after landing. Ebullism This is a quite rare phenomenon, seen at very high altitudes (in excess of 63,000 ft) when the pilot is unprotected by either a pressure suit or pressurised cockpit. This phenomenon occurs owing to the ambient pressure at 63,000 ft being equal to water vapour pressure in the body (both are 47 mmHg). At altitudes in excess of 63,000 ft, the low ambient pressure is insufficient to prevent water in the body moving from the liquid state to the gaseous state. The pressure differential results in an apparent boiling of body fluids at ambient (usually quite cold) temperatures (Beischer and Born, 1957). At sea-level pressures, boiling of a fluid requires the addition of 100°C thermal energy. However, at high altitude the boiling effect is created at ambient temperatures owing to the very low ambient pressure level (less than 47 compared with sea-level of 760 mmHg). From a physiological viewpoint, ebullism can cause extremely serious problems in most body organs, and is often fatal. However, brief exposures can be treatable and survivable (Kolesari and Kindwall, 1982; Murray et al., 2013). Case Study On 5 June 1991, a Royal Australian Air Force F/A-18A Hornet (serial number A21–41) of No 75 Squadron was declared missing after failing to return to RAAF Base Tindal from a routine training mission. The aircraft was being flown by Flying Officer Cameron Conroy. Conroy’s F/A-18 was one of a pair which had been conducting simulated ground attacks on targets almost 300 kilometres south-west of RAAF Base Tindal, in the Northern Territory. Flying Officer Conroy’s wingman flew alongside him when he had failed to respond to radio calls. Conroy was seen to be slumped forward over the controls, unconscious. He was not wearing his oxygen mask. The aircraft was on autopilot, and was tracked by ground-based radar on a constant east-north-east heading. An extensive search failed to find any trace of the aircraft or pilot. The loss of Flying Officer Conroy and Hornet A21–41 was attributed to hypoxia of the pilot. Just over three years later, in July 1994, the wreckage of the Hornet was found some 100 kilometres north-east of Weipa, in far North Queensland. On the twentieth anniversary of the loss of Flying Officer Conroy, a commemorative service was held at RAAF Base Tindal, during which a tree was planted by his widow in Tindal’s memorial garden. This garden was created in honour of Wing Commander Ross Fox, a former Commanding Officer of 75 Squadron, who died on 4 August 1990 after a mid-air collision with another F/A-18. The memorial garden serves to remember and honour members of 75 Squadron who have made the ultimate sacrifice.

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Chapter 3

Acceleration During highly dynamic forms of flight such as air combat manoeuvring, fast jet pilots are exposed to significant levels of acceleration. This acceleration is expressed in terms of the G level, and in manoeuvring flight these are frequently in the order of +5 to +9 Gz. The high G environment is characterised by repetitive exposure to multiple, high-intensity, short-duration G events. In this chapter, the adverse consequences of such high G exposure will be considered, as well as the general countermeasures employed by fast jet pilots to protect them. Firstly, it is important to develop a broad understanding of what is meant by the term G force. The Physics of G An aircraft in flight can experience acceleration that is generated independently of that owing to the force of the Earth’s gravity. When undergoing a turn, the aircraft will undergo acceleration in accordance with Newton’s Laws of Motion. To keep the aircraft travelling in a circle, a force must be acting upon the aircraft, since it is flying at a particular velocity, but the direction of its flight path changes constantly. Thus, there is an acceleration acting upon the aircraft, which is directed towards the centre of the circle it describes, in accordance with Newton’s First Law of Motion. Newton’s Second Law of Motion (F = ma) gives the magnitude of the acceleration, which is the product of the applied acceleration and the aircraft’s mass. The resultant force is known centripetal force, which is directed towards the centre of the circle. In accordance with Newton’s Third Law of Motion (every action has an equal and opposite reaction), there must be an equal yet opposite force balancing the centripetal force. This is known as the centrifugal force, and is directed away from the centre of the circle. The magnitude of the centripetal acceleration (and therefore also the centrifugal acceleration) is a function of the applied acceleration and the radius of the turn, as follows: a = v2/r where



a = acceleration v = velocity r = radius of rotation

Centripetal force, Fc, can then be determined using Newton’s Second Law:

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Fc = mv2/r This equation demonstrates that centripetal force increases with increasing velocity and/or decreasing turn radius. This also holds for centrifugal force, since this is equal in magnitude (but opposite in direction) to centripetal force. Magnitude of G The terms force and acceleration are often used interchangeably in this setting. This is due to force being proportional to acceleration, since mass is constant. This proportional relationship explains why the acceleration environment is usually described as a G force environment. Where does the term G come from, then? G is a dimensionless ratio which expresses the applied acceleration that an object (such as a fast jet) undergoes as a multiple of the normal acceleration owing to Earth’s gravity. This relationship is expressed thus: G = a.g–1 where



a = applied acceleration (developed in the turn as a result of v2/r) g = acceleration due to the Earth’s gravity (9.8 ms–2).

Use of the term G makes the description of acceleration much simpler and more intuitive, by using the acceleration due to the force of the Earth’s gravity as a reference value. Humans experience the force of gravity owing to the Earth constantly. In terms of G, this means that humans are constantly exposed to an applied acceleration of 9.8ms–2, which is thus equal to 1 G. By converting the applied acceleration of a fast jet in a turn into multiples of the Earth’s gravity, the magnitude of the acceleration is thus much more intuitively understood. For example, a fast jet undergoing a turn which generates an applied acceleration of 34.3 ms–2 (based on a given airspeed and turn radius) will experience a G level of 3.5 G (that is, 3.5 times the Earth’s gravity). This equates to 3.5 times the normal force experienced by humans standing on the surface of the Earth. The term G, therefore, is an extremely helpful tool to understand the acceleration environment of a fast jet pilot. It is proportional to the square of velocity and inversely proportional to the radius of the turn. This means, from a practical viewpoint, that G increases as turn radius decreases and/or airspeed increases. In reality, turn radius is a greater determinant of G load than airspeed (since airspeed tends to bleed off in the turn). Direction of G In order to standardise the description of acceleration, a three-axis co-ordinate system has been adopted. This is used by international convention to describe

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the direction of an applied acceleration. Acceleration can be applied in the longitudinal axis (z), the transverse axis (x) or the lateral axis (y). The acceleration is also expressed as either positive (+) or negative (−). For example, a transverse centripetal acceleration acting from chest-to-back is denoted as −Gx, whereas the same acceleration acting in the opposite direction (that is, back-to-chest) is +Gx. This system can be used to describe either an applied acceleration (centripetal) or its inertial (centrifugal) component. In describing inertial vectors, the positive and negative signs are reversed, such that a chest-to-back inertial vector is denoted as +Gx. This reflects the fact that centripetal and centrifugal accelerations are equal in magnitude but act in diametrically opposed directions. It is important to clearly identify which form of acceleration is being described to avoid confusion. During manoeuvring flight, the pilot’s head is generally directed towards the centre of the circle described by the aircraft. The resultant acceleration is in the head-to-foot or +Gz axis (and is generally known as ‘positive G’). Thus, an aircraft undergoing an angular acceleration of 19.6 ms–2 (2 × 9.8 ms–2) is said to be ‘pulling +2 Gz’ (twice the normal acceleration due to gravity). Most aircraft are capable of +2 Gz, whereas modern jet fighter aircraft such as the F-16 are capable of up to +9 Gz. The Gz limits of a particular aircraft are largely determined by aerodynamic and engine performance factors inherent in the aircraft’s design. Figure 3.1 shows the typical +Gz environment of a fast jet (F/A-18) involved in a series of air combat manoeuvring engagements. The large number of excursions to high +Gz levels demonstrates just how physically and physiologically challenging this environment is for the fast jet pilot. 8

7

6

Gz Load

5

4

3

2

1

Time

Figure 3.1

Gz environment of a fighter during air combat manoeuvring

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Physiological Effects of G In general terms, acceleration due to G produces a degree of distortion to the internal organs of the body, and alters the flow of blood and other bodily fluids. When the G force is directed in the head-to-foot (z axis) of an upright person, the organs of the body tend to be displaced somewhat towards the feet, and the delivery of blood from the lower body back towards the heart is made more difficult. From a human performance perspective, the effects of G on the body form a continuum. The first major effect is a simple increase in apparent weight. This will tend to produce a sagging of the soft tissues of the face, and the increased sensation of weight will be a straightforward function of the G level that the person is exposed to. So, at +4 Gz, a person will feel 4 times heavier than normal. This has some significant practical implications for a fast jet pilot. Unassisted escape is impossible at a +Gz level of +3 or more. This means that an ejection seat is necessary to ensure reliable escape from a stricken fast jet (see Chapter 7). If the pilot (or additional crew member) experiences sudden and unexpected G loads of +4 Gz or more, the head will be forced down owing to the +Gz and will not be able to be lifted up again until the G load comes off. Similarly, the arms and legs will weigh proportionally more under high levels of +Gz, but the muscles responsible for their movement will be no stronger. At high +Gz loads of +8 or more, the upper limbs cannot be lifted or moved around the cockpit. The rest of the G continuum of effects involves the cardiovascular system’s inherent difficulties in ensuring adequate supply of blood to the eyes and brain, leading to several significant issues such as visual impairment and loss of consciousness. These issues are all a result of the impact of hydrostatic force. The cardiovascular system can be thought of as a closed loop column of blood. Such a column of fluid in a gravitational field (such as that due to the Earth) creates a hydrostatic force, which pushes the blood downwards to the bottom of the column (in the direction that the gravitational field is applied in). Owing to its orientation in the long axis of the body, the cardiovascular system is by far and away the system most affected by exposure to +Gz acceleration. The hydrostatic force generated is a function of three variables: the magnitude of the gravitational field, the density of the fluid and the height of the column. In human terms, we can consider the density of the fluid (blood) and the height of the column to be essentially unchanging. For a pilot of a fast jet, the gravitational field strength can vary significantly during manoeuvring flight, as the applied acceleration increases (reflected in high +Gz loads). It is this hydrostatic pressure that explains the cardiovascular effects of exposure to +Gz. The more G experienced, the greater the hydrostatic pressure that the cardiovascular system must contend with. The flow of blood to the brain and eyes is diminished by this hydrostatic pressure effect. The cardiovascular system’s relative inability to deal with high levels of hydrostatic pressure results in the various eye and brain symptoms that will now be considered.

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Visual Effects of +Gz As the cardiovascular system is exposed to acceleration, the increasing hydrostatic force is well tolerated up to a certain point. Then, a number of well-defined changes occur. The most significant of these affects the visual system, particularly the retina (Jaeger et al., 1964). The human eye has an internal pressure of around 20 millimetres of mercury (mmHg). As the +Gz load increases, so too does hydrostatic pressure, and the blood pressure near the eye will fall proportionally. This will affect the delivery of blood and oxygen to the retina, resulting in two well-known +Gz visual phenomena: grey-out and black-out. At a level of +3 to +4 Gz, retinal blood flow diminishes as arterial pressure approaches the level of the eye’s internal pressure. The periphery of the retina is affected first, essentially as a function of distance from the blood supply entering the retina. The delivery blood pressure is not sufficient enough to send blood and oxygen to the outer edge of the retina. Peripheral vision therefore becomes impaired, and this phenomenon is known as ‘grey-out’. This loss of peripheral vision manifests itself as a general greying of vision, sometimes with a tunnel vision effect. The visual field may appear to sparkle, while at the same time being severely degraded. It may also occur in an asymmetric fashion, especially if the head is tilted under high +Gz (with the uppermost eye being affected more). Greyout is the first sign to a pilot that he or she is experiencing a degree of +Gz-induced cardiovascular compromise. It is a very common symptom, familiar to almost every military pilot. In a survey of Royal Australian Air Force fighter pilots, 98 per cent reported experiencing grey-out (Rickards and Newman, 2005). At a slightly higher level of acceleration, in the order of +4 to +4.5 Gz, blood flow into the retina is prevented by the higher internal pressure of the eye relative to the driving arterial pressure. Complete loss of vision occurs. This is termed ‘black-out’. This term should not be confused with unconsciousness, with which it is popularly associated. This complete loss of vision typically occurs with the pilot still fully conscious. The pilot is still able to manoeuvre the aircraft, receive radio transmissions, talk, and so on. Their higher cognitive functions are all still intact – it is only their visual input that has been lost. There is no mental impairment or motor skill incapacity. There is an interval of approximately 4–6 seconds between arterial pressure falling below the critical level of 20 mmHg and complete loss of vision. This is due to the existence of a small, short-term reserve oxygen store within the retina itself. Black-out is more significant a symptom than grey-out, as it is an indication to the pilots that they are approaching the physiological limits of their G tolerance. It is, however, less common than grey-out: 29 per cent of RAAF fighter pilots reported experiencing black-out (Rickards and Newman, 2005). Importantly, the symptoms of grey-out and black-out should be considered a visual warning to the pilot of impending loss of consciousness.

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A-LOC A-LOC (Almost Loss of Consciousness) is a relatively newly described +Gz phenomenon that has gained some prominence in recent years. It represents one point on the continuum of G effects, and can be considered to lie between visual symptoms and frank loss of consciousness. A-LOC is defined as +Gz-induced impairment of cerebral function with no corresponding loss of consciousness (Morrissette and McGowan, 2000; Shender et al., 2003). It occurs with short-duration, rapid onset G exposures, such as three seconds at +6 G. An episode of A-LOC generally only lasts a short time, in the order of approximately five seconds, but the incapacity can extend beyond this time to about 10–15 seconds. If the G load is backed off and adequate blood flow is allowed to return to the brain, the symptoms of A-LOC will resolve quite quickly. Typically, the pilot with an episode of A-LOC will experience mental impairment, often with a loss of situational awareness. The symptoms are many and varied, and are said to depend on which part of the brain is affected. Cognitive, physical, emotional and physiological signs and symptoms have all been described, including sensory abnormalities(twitching of the hands, immobility, numbness and tingling), euphoria, amnesia, apathy, loss of short-term memory, difficulty in forming words, and reduced auditory acuity (Morrissette and McGowan, 2000; Shender et al., 2003). Often A-LOC is said to be associated with the disconnection between the desire and the ability to perform an action (Morrissette and McGowan, 2000; Shender et al., 2003). The pilots can generally see and hear, but doesn’t care about or adequately attend to what they are seeing and hearing. In a survey of A-LOC symptoms in operational fighter pilots, Morrissette and McGowan (2000) reported that 14 per cent of fighter pilots (from the US Air Force, US Navy and US Marines) had experienced A-LOC symptoms including motor, sensory and cognitive abnormalities. In a study involving fighter pilots from the Royal Australian Air Force, at least one A-LOC symptom (not associated with G-LOC) was reported by 52 per cent of the pilots (Rickards and Newman, 2005). In a controlled centrifuge study, Shender et al. (2003) reported 66 A-LOC incidents out of a total of 161 +Gz pulse exposures, a rate of 41 per cent. The operational hazards associated with pilots experiencing A-LOC can be as dangerous as a complete loss of consciousness. The short-term loss of situational awareness and cognitive impairment, especially if they occur during a critical phase of flight, represent a significant flying safety hazard. G-LOC The rapid application of high +Gz forces can overwhelm the cardiovascular system’s ability to maintain blood flow to the brain. The driving pressure generated by the heart is insufficient to overcome the magnitude of the hydrostatic force

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produced by the high +Gz loads. Blood flow to the brain ceases, and the pilot will lose consciousness. This is known as G-induced loss of consciousness (G-LOC). It typically occurs (for a relaxed, unprotected subject) at +4.5 to +5.5 Gz. It is a significant hazard to a fast jet pilot. G-LOC has been formally defined as ‘a state of altered perception wherein (one’s) awareness of reality is absent as a result of sudden, critical reduction of cerebral blood circulation caused by increased G force’ (Burton, 1988b). G-LOC can be regarded as the most dire consequence of exposure to accelerations greater than +1 Gz. There is an important period from the onset of high +Gz during which the brain is able to still function despite the absence of any effective cerebral blood flow. This has been described as the functional buffer period, and has in several studies been shown to have a duration of approximately 6 seconds (Burns et al., 1991; Gillingham, 1988). This buffer period is due to stored oxygen within the brain. This buffer period is generally considered to have a protective role, in that it allows for large scale accelerations to be tolerated as long as they are not sustained for longer than a few seconds. At the end of this period, consciousness terminates abruptly with complete cerebral shut-down. An episode of G-LOC has several features that have been well described in the aerospace medicine literature. In simple terms, a G-LOC episode will result in a period of unconsciousness followed by a period of disorientation and confusion. In operational terms, the total amount of time that the pilot is not in control of his aircraft is termed the total incapacitation period. This period consists of an absolute incapacitation period and a relative incapacitation period (Houghton et al., 1985; Ross, 1990; Whinnery, 1989, Whinnery et al., 1987; Whinnery and Shaffstall, 1979). The absolute incapacitation period represents complete incapacitation or true unconsciousness, which usually lasts for about 15 seconds (Whinnery and Shaffstall, 1979). In experimental terms, it is defined as the time from the subject’s head dropping at the moment of unconsciousness to the raising of the subject’s head as consciousness is restored. This absolute incapacitation period is then followed by a period of relative incapacitation with a duration of approximately 10–15 seconds (Whinnery et al., 1987). This period is defined as the time interval from raising of the head to the first voluntary, purposeful limb movement. During the relative incapacitation period, the pilot is once again conscious, but only in a technical sense. That is, while cerebral blood flow has been restored, the pilot is somewhat dissociated from their situation and unable to function appropriately. The pilot is disoriented and confused, with significant cognitive slowing, and their higher cortical centres are largely dysfunctional (Gillingham, 1988; Whinnery et al., 1987). As a result, the pilot is incapable of appropriately assessing their situation and thus perceiving danger. Fine motor control is absent, and often only gross motor acts are carried out. The pilot is thus still incapacitated inasmuch as they are unable to save themselves or correct their situation. The pilot is still recovering from the major insult that their brain has sustained as a result of inadequate blood and

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oxygen delivery. Obviously, in a fast jet pulling high +Gz levels at low altitudes, the potential for disaster in such a situation is enormous (Lamb et al., 1960). For effectively 30 seconds the pilot is not flying the aircraft. There is also a characteristic recovery process from an episode of G-LOC. Tingling in the extremities and perioral numbness have been reported (Whinnery, 1988). Convulsions and flailing of the arms commonly occur, generally coinciding with the re-establishment of effective cerebral blood flow. Typically these convulsions occur in the latter third of the absolute incapacitation period, generally in the last 4 seconds of this so-called convulsion-prone period, and are not associated with any underlying structural abnormalities of the brain (Whinnery, 1989). In addition, cognitive distortions of a dream-like nature are said to occur towards the very end of the absolute incapacitation period (Forster and Whinnery, 1988). These dreams can often incorporate the convulsions which typically occur in the same phase of the G-LOC event. G-LOC also has a number of neuropsychological effects, which are accentuated by repeated G-LOC episodes. These include denial, euphoria, irritation, embarrassment, confusion, dissociation and anxiety, among others (Forster and Cammarota, 1993; Whinnery and Jones, 1987). It has been reported that G-LOC has the potential to ‘exert a temporary psychologically crippling effect’ on the combat effectiveness of tactical aircrew, who may have altered judgement, and a loss of aggressiveness and motivation to carry out their mission (Whinnery and Jones, 1987). In the post-G-LOC period, psychological mechanisms often result in suppression and denial of the actual G-LOC event. In approximately 50 per cent of cases, recovery from G-LOC is associated with event amnesia, with the pilots not recollecting having had a period of unconsciousness at all. As far as they are aware, they have been awake and in control of their aircraft for the whole sortie. These post-G-LOC psychological reactions can have a negative impact on flight safety. Full psychophysiological recovery from an episode of G-LOC is only reached after a complete sleep cycle. Prevalence of G-LOC Many nations have reported their G-LOC prevalence rates. The observed rate of G-LOC in published international studies ranges from 8 to 19 per cent (Alvim, 1995; Green and Ford, 2006; Rickards and Newman, 2005; Yilmaz et al., 1999). In the UK, 19 per cent of Royal Air Force pilots surveyed had experienced a G-LOC event during their flying career (Green and Ford, 2006). In the Royal Australian Air Force, a survey involving F/A-18 and Hawk 127 pilots revealed a 9 per cent rate of G-LOC, and in 50 per cent of cases these involved the flying pilot (Rickards and Newman, 2005). In the USAF, G-LOC events by aircraft type showed that the higher the G capability of the aircraft, the higher the reported G-LOC rate. Twelve per cent of USAF tactical pilots have had a G-LOC event (Pluta, 1984). Twenty-eight per cent of F-16 G-LOC events result in the loss of the aircraft and/or the pilot. In the US

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Navy, 12 per cent of pilots admit to experiencing a G-LOC event (Johanson and Pheeny, 1988). These prevalence figures may only represent 50 per cent of actual G-LOC events owing to the lack of recall when pilots regain consciousness and the possible reluctance to admit these symptoms for fear of being removed from flight status and issues of self-esteem (Whinnery et al., 1987). For all the reported G-LOC events from current surviving pilots, many more probably go unreported and a number of fatal accidents may be the result of G-LOC, but cannot be definitively classified as such. Clearly, then, G-LOC is still a major ongoing hazard for fast jet aircrew. Clinical G Problems +Gz-induced Neck Injuries Gz-induced neck injuries are a common problem for fast jet pilots regularly exposed to the high +Gz environment (Albano and Stanford, 1998; Andersen, 1988; Coakwell et al., 2004; Green, 2003; Hamalainen et al., 1994b; Newman, 1996; Newman, 1997a; Wagstaff et al., 2012). Wearing a helmet and oxygen mask increases the weight of the pilot’s head, and the neck muscles thus have to do much more work during air combat manoeuvring in order to maintain visual contact with the adversary aircraft. As a result, neck injuries are common. Knudson et al. (1988) reported that 74 per cent of surveyed F/A-18 pilots had experienced neck pain with high +Gz. Vanderbeek (1988) reported a period prevalence rate for this injury of 50.6 per cent among a large number of USAF fighter pilots. Yacavone and Bason (1992) reported a period prevalence among US Naval aviators with G-induced neck pain of 26.8 per cent. A prospective study of student fighter pilots in Finland produced a cumulative incidence of 37.9 per cent (Hamalainen et al., 1994a), while a survey of Japanese F-15 pilots revealed a rate of 89.1 per cent (Kikukawa et al., 1994). In a Royal Australian Air Force study, the incidence of G-induced neck injuries in RAAF fighter pilots was 85 per cent. Thirty-eight per cent of the pilots reported their neck injury as having interfered with mission completion, which demonstrates the operational significance of these common injuries (Newman, 1997a). Despite the widespread prevalence, a solution to this problem has not yet been developed. Exercise and muscle conditioning programmes have been recommended, as have neck positioning strategies, but no one single solution has proven to be the answer (Coakwell et al., 2004; Newman, 1997b). Respiratory Effects Several respiratory effects of +Gz have been identified. Exposure to high levels of +Gz accentuates the regional differences in ventilation and perfusion that exist

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within the lungs of a normal upright individual at +1 Gz. As the level of +Gz increases, the lungs become heavier and the pressure gradient down the pleural cavity increases. The result of this is progressive increase in the size of the upper air spaces, with a concomitant reduction in size of the lower air spaces. With increasing +Gz, alveoli at the base of the lung can attain their minimum volume with subsequent airway collapse. This particular +Gz-induced respiratory condition is known as acceleration atelectasis, and occurs due to the combined effects of 100 per cent oxygen, at least +3 Gz and the wearing of a G-suit. The pilot may experience some shortness of breath and coughing, and pain on deep inspiration (which ultimately reinflates the lower lung and fixes the problem after flight). Countermeasures for this include dilution of the inspired oxygen concentration by inert gas (for example, nitrogen), the use of positive pressure breathing, and performing an anti-G straining manoeuvre (Tacker et al., 1987). The applied +Gz causes an increased perfusion gradient down the lungs, with more blood going to the bases and less to the apices. At +4 to +5 Gz the upper half of the lungs is effectively not perfused. The combination of these ventilation and perfusion changes under +Gz leads to a considerable ventilation-perfusion mismatch. This can lead to a reduction in arterial oxyhaemoglobin saturation, which is approximately 85 per cent at +5 Gz (compared with the normal 98 per cent at +1 Gz. This effect can be offset by the pilot breathing a higher oxygen concentration (up to 100 per cent). +Gz also increases the physical work of breathing. The +Gz acceleration forces the diaphragm and abdominal contents downward, and the chest wall becomes proportionally heavier, requiring more effort. At higher levels, the work of breathing increases due to reduced lung compliance. An increase in respiratory work of some 55 per cent at +3 Gz has been reported. At +5 Gz, total lung capacity is reduced by approximately 15 per cent. Miscellaneous G Effects There are several other effects of +Gz that warrant a brief mention. High +Gz exposure can lead to rupture of skin capillaries in dependent, unprotected (that is, not covered by a G-suit) parts of the body. This results in cutaneous petechiae formation (known as ‘G measles’), which can be spectacular and widespread. It does, however, resolve quickly over a few days. Non-pathological, transient cardiac arrhythmias such as premature ventricular contractions have been frequently reported during and immediately after +Gz exposure, owing to a combination of catecholamine release, cardiac deformation and increased sympathetic drive (Balldin et al., 1999; Comens et al., 1987). There is a +Gz-induced endocrinological response, with rises documented in anti-diuretic hormone (ADH), adrenalin and cortisol in response to the stress of the acceleration. Various biochemical markers have been found to change as a result of +Gz exposure (Comens et al., 1987). +Gz-induced proteinuria has been observed, which has been attributed to severely reduced renal blood flow

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(Noddeland et al., 1986). Fatigue is often associated with +Gz, due to the physical stress involved. G Tolerance A fast jet pilot’s tolerance to +Gz loads is a multi-factorial phenomenon. There are a number of factors that are known to adversely affect a pilot’s +Gz tolerance on a given day. These include dehydration, fatigue, hypoxia, the effects of alcohol, and physical conditioning (Balldin, 1984; Burton, 1986; Cooper and Leverett, 1966; Gillingham, 1987; Hrebien and Hendler, 1985; Newman et al., 1999; Webb et al., 1991; Whinnery, 1979; Whinnery and Parnell, 1987). Avoiding or minimising the effect of these factors that lower or reduce G tolerance is important. It is also true that there is a degree of individual variation in terms of +Gz tolerance, with some people having better inherent +Gz tolerance than others for no apparent reason. Similarly, it must be remembered that every pilot can have ‘good G days’ and ‘bad G days.’ Being unprepared for the +Gz exposure is also a tolerance-reducing factor. The flying pilot, by virtue of awareness of what manoeuvre they are about to execute, coupled with the physical manipulation of the controls, tends to have a better tolerance of the subsequent +Gz load than another occupant of the aircraft who is unprepared and unaware of what is about to happen. This surprise effect can reduce their tolerance to the +Gz. The rate of onset and offset of high +Gz has been shown to affect the nature of the subsequent G-LOC episode. Gradual onset of +Gz results in longer absolute and relative incapacitation periods. This is due to the longer period of absent or reduced cerebral perfusion during gradual onset exposure. The physiological consequences of exposure to high +Gz forces as discussed above represent a cardiovascular spectrum. This spectrum is dependent on the rate of application of the +Gz force. As discussed previously, the onset and offset rates of applied +Gz can affect the time of incapacitation if G-LOC results. The rate of +Gz application is also important in terms of the appearance of symptoms prior to the occurrence of G-LOC. The critical G onset rate in this context is 2 Gs−1. If the rate of application of G is less than this critical value, then the cardiovascular system will experience the entire spectrum of +Gz effects. That is, grey-out will occur at +3 to +4 Gz, followed by black-out at +4 to +4.5 Gz and G-LOC at +4.5 to +5 Gz. If the rate of onset is higher than this value, loss of consciousness is too rapid for the other effects to be experienced. The pilot may thus bypass the earlier signs of cardiovascular compromise and proceed straight to G-LOC. In modern fast jet aircraft engaged in air combat manoeuvring, Gz onset rates can often be at the design limits of the aircraft, resulting in onset rates as high as +15 Gs−1. At lower rates the visual symptoms can be used as an early warning or premonitory sign of approaching G-LOC. In practical terms, however, this does not often occur, for the fighter pilot needs to manoeuvre his aircraft quickly

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and forcefully during an ACM engagement, resulting in high G onset rates with consequently no visual warning signs. The cardiovascular system, it must be remembered, does not sit passively by while cerebral blood flow deteriorates owing to high +Gz loads. The falling blood pressure at head and neck level owing to high +Gz triggers a compensatory response by the arterial baroreflex system, designed to restore head-level blood pressure back to normal. This system measures blood pressure in the major neck arteries, and once the pressure falls due to +Gz application, the reflexes trigger an increase in heart rate, an increase in cardiac contractility (a more forceful heart contraction per beat) and an increase in vascular tone throughout the body (to reduce the pooling of blood in the lower body). These measures in combination attempt to restore blood pressure towards normal, but take some 6 to 12 seconds to exert their maximal effect. As seen in the Stoll curve, the +Gz threshold for visual symptoms increases as the baroreflex exerts its effect. This system cannot cope with the high +Gz onset rates of a modern fast jet. Regular exposure to the high +Gz environment improves overall tolerance. Most fast jet pilots have been aware of this for many years, but it is only in recent years that scientific evidence of this has been documented (Convertino, 1998; Newman et al., 1998; Newman and Callister, 2000; Newman and Callister, 2008; Newman and Callister, 2009). Regular high +Gz exposure leads to cardiovascular adaptation, with the compensatory baroreflex system becoming more effective and efficient at dealing with the dynamic +Gz-induced blood pressure changes (Newman et al., 1998; Newman et al., 2000; Newman and Callister, 2008). G Protection Measures Given the risk of G-LOC, it is clearly essential for pilots to be protected from the adverse consequences of high +Gz exposure. There are several protective strategies that fighter pilots can use to combat the potentially dangerous effects of high G. One obvious strategy is to avoid the various factors described above that lower +Gz tolerance, such as alcohol, dehydration and fatigue. Beyond that, exposure to high +Gz requires the use of one or more of the several countermeasures that have been designed to protect the fighter pilot from the deleterious and potentially dangerous effects of +Gz acceleration. In terms of the G-time tolerance curve, anti-G countermeasures are designed to shift the curve upwards, so that the G-LOC region cannot be entered at the end of the functional buffer period. With appropriate and fully optimised anti-G countermeasures, the fighter pilot can withstand +Gz levels of up to +9 Gz for short periods of time. G-Suits The G-suit is worn externally over the lower half of the body. It consists of five interconnecting pneumatic bladders, one of which compresses the lower abdomen

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and the remaining four compress both thighs and both calves. The bladders are contained within a non-distensible fabric cover, and provide somewhere in the region of 30 per cent coverage of the lower body. Inflation of the G-suit is achieved via a source of bleed air from the compressor stage of the jet engine, delivered to the bladders through a hose connected to an anti-G valve (Burton, 1988a; Burton and Shaffstall, 1980). The standard anti-G valve fitted to most fighter aircraft is a mechanically operated device which controls the pressure and rate of inflation of the G-suit bladders. Inflation is generally delayed until a level of +1.75 to +2 Gz is reached. Inflation of the suit continues until a maximum inflation pressure of 1.25 lb/sq. inch/G (8.6 kPa) is achieved. As the suit inflates in proportion to the +Gz load, the calves, thighs and lower abdomen of the pilot are compressed. This encourages venous return to the heart, prevents dilatation of the capacitance vessels of the lower limbs, and the abdominal bladder acts to splint the diaphragm and prevent the downward displacement of the heart. Total peripheral resistance is thus increased by the G-suit, which delays the filling of the capacitance vessels. Several advanced technology G-suits which rely on extended bladder coverage (80–90 per cent) are in service with several air forces, and these tend to provide a higher level of G protection than the standard G-suit (around +2 to +2.5 Gz worth of protection compared with the standard suit’s +1 to +1.5 Gz). Failure of the G-suit during manoeuvring flight will lead to greatly reduced G protection. In a survey of F-16 and F-15 pilots, G-suit malfunction was the cause of 19 per cent of G-LOC events (Sevilla and Gardner, 2005). Anti-G Straining Manoeuvre The Anti-G Straining Manoeuvre (AGSM) involves repetitive 3-second cycles of expiratory effort (straining) against either a partially or completely closed glottis, in conjunction with isometric tensing of the lower limb musculature and abdominal wall The increased intrathoracic pressure developed by the AGSM is transmitted directly to the vascular system, promoting cerebral blood flow. The timing of the strain cycle is important. If the increased intrathoracic pressure is maintained for more than three seconds, venous return from the lower limbs is significantly reduced, and the AGSM becomes a counterproductive exercise. If the cycle is less than three seconds, the subject is in danger of hyperventilating, which carries the risk of unconsciousness in its own right. Timing the cycle accurately is thus of paramount importance in terms of effectiveness. If performed properly, the AGSM will give up to +3 Gz protection, but is extremely fatiguing (Buick et al., 1992; Lyons et al., 1997; Whitley, 1997). Several studies have shown that G-LOC is most commonly caused by an improperly performed AGSM (Rayman, 1973; Whinnery, 1986). In a survey of F-16 and F-15 pilots, 72 per cent of G-LOC events were attributed to poor anti-G strain (Sevilla and Gardner, 2005). In a US Navy study, 53 per cent of pilots experiencing A-LOC symptoms were not performing an AGSM at all (Morrissette and McGowan, 2000).

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Positive Pressure Breathing Positive pressure breathing for G protection (PBG) involves breathing air which is progressively pressurised as the applied +Gz load increases. Pressure breathing is quite unlike normal breathing, and for a pilot to perform it safely and properly in the air they must receive specific ground-based training. The central underlying idea with PBG is effectively one of converting the usual AGSM into an automatic process requiring little conscious effort on the part of the pilot while achieving a similar +Gz tolerance outcome. PBG exploits the physiological consequences of delivering breathing air under pressure to the lungs. The pressure of the air in the lungs is essentially transmitted to the heart and great vessels within the chest cavity on an almost 1:1 basis. Normally with an AGSM the straining activities of the pilot generate an elevated intrathoracic pressure, which is transmitted to the blood vessels and heart. With PBG, however, the same effect is achieved via the delivered high pressure air, without the need to actively strain on the part of the pilot (Ackles et al., 1978; Burns and Balldin, 1988; Domaszuk, 1983; Harding and Bomar, 1990; Lauritzsen and Pfitzner, 2003; Pecaric and Buick, 1992; Shaffstall and Burton, 1979; Travis and Morgan, 1994). The pressure in the thoracic cavity due to PBG effectively pushes the blood upwards and out of the chest, towards the brain. This is the crucial element, in that it helps maintain perfusion of the brain in the face of the significant +Gz challenge, thus ensuring the pilot remains conscious due to the continued supply of oxygen. At the same time, the pressure is also transmitted to the venous side of the circulation, which helps maintain the arterio-venous pressure gradient, thus allowing for the normal flow of blood to and from the brain. Positive pressure is delivered according to a pressure schedule. With most PBG systems, positive pressure starts feeding in at around +4 to +5 Gz, and increases in a linear fashion with increasing +Gz load, reaching a level of 60 mmHg positive pressure at +9 Gz (Pecaric and Buick, 1992; Travis and Morgan, 1994). The two main advantages of PBG are the ability to tolerate a higher numerical value for +Gz, but more so the ability to tolerate operationally normal +Gz levels for longer periods with a much reduced fatigue penalty (Ackles et al., 1978; Burns and Balldin, 1988; Eiken et al., 2003; Lauritzsen and Pfitzner, 2003; Shaffstall and Burton, 1979; Tong et al., 1998b). The pressure associated with PBG not only boosts head-level blood pressure but also helps take care of inspiration (making it essentially passive rather than active). These features have the overall effect of reducing the pilot’s physiological workload while simultaneously improving headlevel blood pressure and oxygen delivery to the brain (Ackles et al., 1978; Burns and Balldin, 1988; Eiken et al., 2007; Lauritzsen and Pfitzner, 2003; Njemanze et al., 1993; Shaffstall and Burton, 1979;Tong et al., 1998b).

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Centrifuge Training Many air forces now make use of human centrifuges. These devices allow a pilot to sit in a simulated cockpit and experience high +Gz forces in a controlled and supervised way. This allows the pilots to not only gain confidence and experience in dealing with the effects of high +Gz force, but also to perfect their AGSM prior to flying the actual fighter aircraft. The modern human centrifuge is a remarkably sophisticated device that can combine flight simulation with a high +Gz environment to produce a highly realistic flight experience for the fighter pilot. The centrifuge is able to generate a level of +Gz acceleration equivalent to a fighter aircraft, albeit in a safe and reliable manner. The development of sophisticated man-in-the-loop active control systems now allows the pilot in the centrifuge to ‘fly’ the device, generating +Gz via control column inputs as they would in the actual aircraft. Coupled with an out-the-window view, accurate aircraft flight model, and comprehensive terrain and navigational databases, the centrifuge can virtually reproduce the aircraft flight envelope on the ground. Centrifuge training can reduce the incidence of G-LOC. The USAF G-LOC rate in the period 1982–84 was 4 events per million flight hours. A centrifuge training programme was implemented in the USAF in 1985, with the result that the G-LOC rate in the following period 1985–90 was reduced to only 1.3 G-LOC events per million flight hours. The reduction in the G-LOC rate was attributed to the introduction of the centrifuge training programme (Lyons et al., 1992). The Turkish Air Force had a G-LOC rate of 10 per cent in 1992, but after the introduction of centrifuge training, this incidence rate decreased to 6 per cent by 1996 (Yilmaz et al., 1999). The rate reduction was attributed to AGSM instruction and improved technique over time through the centrifuge training programme. Interestingly, Morrissette and McGowan (2000) found that 68 per cent of those reporting A-LOC symptoms had received centrifuge training, compared with 26 per cent who did not report A-LOC. They suggested that this was due to a greater awareness and subsequent reporting of the associated symptoms in centrifuge-trained pilots. A Glimpse into the High G Future As discussed in Chapter 1, the next generation of fighter aircraft are so-called ‘super-agile’ aircraft. These are designed with improved flight control systems and control laws, against extremely relaxed stability criteria, and often make use of vectored thrust technology. While conventional fighter aircraft have a +Gz environment predominantly in the Gz axis (Newman and Callister, 1999), superagile aircraft are capable of performing manoeuvres with rapid, multi-axis motion. They are able to operate in the post-stall regime of the flight envelope, at very low speeds and high angles of attack (AOA) with full flight control authority. Indeed, some super-agile aircraft have demonstrated AOAs in the order of 70° and beyond (Alcorn et al., 1996; Boyum et al., 1995; Ericsson, 1995).

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These aircraft will expose the aircrew to a more complex G environment, involving the combination of multi-axis acceleration (Gx, Gy and Gz), high rate of G change, rapid transitions and rotational motions. This environment has significant implications for the aircrew, and the potentially adverse nature of this multi-axial G environment has been recognised by several authors (Coakwell et al., 2004; Frazier et al., 1982; Newman, 2006). The multi-axial force environment can increase the likelihood of neck injury, given that the unrestrained head-neck complex will bear the brunt of these forces. The G-induced neck injury risk is exacerbated by the weight of the helmet and oxygen mask, the forward centre of gravity of the oxygen mask assembly, and the use of any helmet-mounted sighting and display systems (Hamalainen, 1993; Newman, 2006). In a study that mathematically modelled the geometry of super-agile flight manoeuvres, Newman and Ostler (2011) found that high AOA velocity vector rolls would lead to significant lateral G loads being imposed on the head and neck of the pilot, up to 6.7 Gy at an AOA of 70° and a roll rate of 200°/sec. These lateral G loads have significant potential to increase the prevalence of neck injuries in super-agile aircraft pilots. Other researchers have found that high roll rates can lead to incapacitation of the pilot (Alcorn, 1996). Super-agile flight also raises important questions in terms of the potential for spatial disorientation, the performance requirements of ejection seats and tolerance of the cardiovascular system to complex multi-axial G environments (Albery, 2004; Newman, 1998). The human performance and biomechanical implications of super-agile flight remain to be fully understood. A thorough understanding of the complex acceleration environment of these future aircraft is necessary, in order to develop appropriate countermeasures for improving pilot tolerance of this challenging form of flight. Case Study On 1 September 1998, a United States Air Force F-16C Fighting Falcon from the 523rd Fighter Squadron was more than an hour into a tactical intercept training mission. The experienced pilot had 2,425 flying hours including 950 hours in the F-16. While performing a high +Gz manoeuvre, the pilot suffered a G-LOC event. The pilot was unconscious for approximately 10 seconds. On regaining consciousness, the aircraft was found to be in a 70-degree dive, at an airspeed of 575 knots passing through an altitude of 5,000 feet. The pilot immediately attempted to recover from the dive, but then ejected from the aircraft at an altitude above ground level of 300 feet. The pilot survived but sustained serious injuries. The aircraft was completely destroyed. The primary cause was determined to be an improperly executed AGSM and a malfunctioning G-suit due to a disconnected hose while at +6. 4 Gz.

Chapter 4

Spatial Disorientation Flying a fast jet requires a pilot to operate in a dynamic, three-dimensional environment. While this can expose the pilot to many potential threats, one of the most significant is Spatial Disorientation (SD). Indeed, while SD is a risk factor for all pilots (Moser, 1969; Newman, 2007; Sipes and Lessard, 2000), several studies have shown that SD is a much more common problem for fast jet aircrew (Cheung et al., 1995; Holmes et al., 2003). Definitions The definition of spatial disorientation (SD) is as follows (Benson, 1988): Spatial disorientation is a term used to describe a variety of incidents occurring in flight where the pilot fails to sense correctly the position, motion or attitude of his aircraft or of himself within the fixed coordinate system provided by the surface of the Earth and the gravitational vertical. In addition, errors in perception by the pilot of his position, motion or attitude with respect to his aircraft, or of his own aircraft relative to other aircraft, may also be embraced within a broader definition of spatial disorientation in flight.

Failure to recognise a spatial disorientation event in flight may lead to loss of control of the aircraft or controlled flight into terrain (CFIT) with loss of an expensive fast jet and highly trained aircrew. Spatial disorientation has been broadly classified into three main types. These types are Type I (unrecognised), Type II (recognised) and Type III (incapacitating). It has been argued by some researchers that these numerical types are not especially helpful, and that using the descriptor (recognised, unrecognised and so on) is a more intuitive approach (Cheung et al., 1995). However, these terms are in common usage and warrant further description here. Type I (Unrecognised) In this form of disorientation, the pilot is unaware that they are disoriented or that they have lost situational awareness. This form of spatial disorientation is clearly dangerous, and by far away accounts for the majority of spatial disorientation accidents and fatalities in the fast jet community (Cheung et al., 1995; Lyons et al., 2006). In a USAF study of 13 fast jet SD accidents, all were Type I (Lyons

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et al., 1994). A similar study in the Canadian Forces found 12 out of 14 fast jet SD accidents were also Type I (Cheung et al., 1995). In a subsequent USAF study examining fast jet SD accidents in the period 1993–2002, Type I SD was present in 92 per cent of the accidents, and in 17 there was no attempt by the pilot to either recover the aircraft or eject (Sundstrom, 2004). Type II (Recognised) Type II SD is more common than Type I, but does not generally lead to accidents. In this form of disorientation, the pilot recognises that there is a problem, which may be either a mismatch between sensory perception and the flight instruments, or the aircraft being in an unusual attitude. Recognition of the sensory mismatch or unusual attitude created by the SD phenomenon then prompts the pilot to take appropriate action, such as recovery from the unusual attitude to straight and level flight. In so doing, a spatial disorientation accident is thus avoided, and the pilot will have received an important first-hand in-flight demonstration of spatial disorientation and how to successfully recover from it. It is the failure to recognise SD that leads to fatal accidents. A US Navy study examining SD-related incident data for the period 1980–89 found that fast jet pilots suffered predominantly Type II SD during daytime flight operations, generally in association with high workloads and +Gz exposure (Bellenkes et al., 1992). Type III (Incapacitating) Type III SD is the most extreme form of disorientation stress (Newman, 2007). The pilot may recognise the disorientation, but is unable to successfully recover from the situation owing to being cognitively overwhelmed. This may be more likely in high workload situations where fatigue may also be present (Newman, 2007). The pilot may struggle for control of the aircraft all the way to ground impact, having never once achieved full control. Fortunately, in the fast jet community Type III SD is an infrequent type of SD event. In a US Navy study, no Type III events were found in 33 SD-related incidents (Bellenkes et al., 1992). This could be due to the high level of training of the military fast jet pilot, and their relative familiarity with high workload conditions and high cognitive demands. Prevalence of Spatial Disorientation Several surveys and accident analysis studies have tried to determine the overall prevalence of SD in fast jet pilots. While some authors have commented on the likely under-reporting of SD and the different study methodologies applied (Gibb et al., 2011; Newman, 2007), the consistent finding is of a high prevalence of SD in fast jet pilots with significant cost in terms of aircrew lives and aircraft lost.

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Furthermore, despite years of research and training, the prevalence of SD shows little sign of decreasing. A brief review of some of the published studies shows the magnitude of the problem in the fast jet community. The USAF has looked at SD prevalence several times. Accident data during the period 1990 to 2004 show that SD was more common (twice as likely) in fast jet aircraft than training and transport aircraft, and accounted for 11 per cent of all USAF accidents and 69 per cent of accident fatalities in that period (Lyons et al., 2006). A USAF study found that single-pilot aircraft might be more at risk from SD, and that a third of F-15 and F-16 accidents studied were attributable to SD (Gillingham, 1992). Another study examined F-16 Class A accidents between 1975 and 1993, and found that 7.5 per cent were due to spatial disorientation (Knapp and Johnson, 1996). Sundstrom (2004) examined the period 1993–2002, and found that SD was identified as either a contributing or causal factor in 25 fast jet aircraft accidents (A-10, F-15E, F-16 and F-117), with 19 fatalities, the loss of 24 aircraft and a financial cost to the USAF of more than $450 million. Studies in other countries show similar results. In Canada, 50 per cent of Canadian Forces (CF) pilots reported experiencing SD, and for the years 1982 to 1992, SD was implicated in 22.5 per cent of all accidents in the Canadian Forces. Forty-four per cent of CF-18 pilots reported experiencing SD, with 10 per cent reporting more than three episodes of SD (Cheung et al., 1995). A study in the Netherlands Air Force found that F-16 pilots experienced more SD than other fast jet aircraft pilots (Holland and Freeman, 1995). In the UK, fast jet pilots in the Royal Air Force experienced more body sense illusions and flight display illusions than other aircrew (Holmes et al., 2003). In RAF fast jet pilots, the top 5 SD illusions in rank order were the leans, loss of horizon due to atmospheric conditions, misleading altitude cues, sloping horizon, and the Coriolis illusion (discussed in later sections). Distraction owing to task saturation was reported in 66 per cent of respondents, a finding similar to other studies (Holmes et al., 2003; Sipes and Lessard, 2000). While the emphasis of most of these studies is in analysing accident data and determining prevalence rates, it must be remembered that SD can also significantly degrade pilot performance and reduce fast jet mission effectiveness (Cheung and Hofer, 2003). This is an important consideration in the tactical operational environment. Underlying Mechanisms In order to fulfil their mission, it is important that the fast jet pilot has some idea of where they are in space. Humans are equipped with a sophisticated set of sensory systems that provide information on orientation. These specialised sensory systems are the balance organs located in the inner ears (the vestibular system), the visual system, and the proprioceptive system (the ‘seat-of-the-

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pants’). The contributions of these systems are not equally weighted – the visual system is dominant and provides approximately 80 per cent of the raw orientation information (Newman, 2007). The contributions of the vestibular system and the proprioceptive system account for 10 per cent each. The vestibular system is an important mechanism for orientation. It consists of two important components: the semi-circular canals and the otolith organs. There are three semi-circular canals in each ear, and in functional terms they operate as three matched pairs of angular accelerometers, in each of the three primary axes of motion. Significantly, they have a stimulation threshold of 2°/sec2, below which they are not able to detect angular motion. In the flight environment, this is important – if a turn is made (intentionally or otherwise) at a rate of angular acceleration less than this threshold, the canals will not detect the turn, and the pilot will similarly not be aware that they are turning and will feel as if they are straight and level. This is the basis for most vestibular illusions. Each ear has two otolith organs, one acting in the vertical plane and the other acting in the horizontal plane. The otoliths are linear accelerometers, and under normal conditions the vertical otoliths transduce the force of gravity due to the Earth (that is, +1 Gz). The visual system is of fundamental importance to correct orientation. This is highlighted by the fact that in condition with poor or absent visual cues (such as bad weather flying or night operations) SD is much more likely to occur. This is due to orientation information being based on vestibular and proprioceptive information, which is prone to inaccuracy. Given that the visual system is the dominant system for normal orientation, a visual illusion can be very powerful. Visual illusions can occur even in perfect weather, and in many cases the illusions that occur depend on expectations of what the pilot ‘should’ be seeing. Good visual sensory information can dominate and suppress graviceptive information from the vestibular system (Eriksson et al., 2008). Peripheral vision plays a major role in this process, particularly when there is good visual scene flow and a field of view rich in content (Eriksson et al., 2008). This significant visual input tends to override any false or inaccurate vestibular input. However, in the Proprioceptive System

Visual System

Brain

Vestibular System

Figure 4.1 Spatial orientation mechanisms

Orientation Sense

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absence of such visual input the vestibular system’s information can come to the fore, resulting in an illusory perception that might result in an illusion. The proprioceptor system consists of pressure sensors throughout the body, especially in the joints, tendons, ligaments, muscles and skin. Under normal conditions, the pressure exerted on a given set of pressure receptors helps contribute to the overall sense of orientation. For example, the pressure receptors in the soles of the feet and the joints of the ankle and knee signal to the brain that upright posture is being maintained. The brain is responsible for integrating the incoming information into a single accurate model of orientation. The integrated model is used to determine our position within a fixed coordinate system provided by the surface of the Earth (as a horizontal reference) and the force of the Earth’s gravity (which provides a vertical reference). This integration process is complex and based on continuous updating and cooperative exchange of sensory information within and between the various sensory components, in order to give immediate and accurate orientation information (Newman, 2007; Tribukait and Eiken, 2006). In particular, the visual and vestibular systems are tightly connected via extensive neural pathways. There are fundamental physiological and psychological limitations inherent to humans that contribute to the loss of orientation in the flight environment. The sensory systems evolved over time in a terrestrial environment consisting of low velocities and low levels of acceleration. They are not optimised to operate in the three-dimensional environment of flight, where it is possible to operate independently of the normal visual cues (for example, bad weather or night flying) and in a variable gravitoinertial force environment (Newman, 2007). The otoliths cannot distinguish between gravity and linear accelerations, and the semicircular canals cannot detect very low rates of angular acceleration. The complex movements of a pilot’s head and/or the aircraft during manoeuvring flight can make accurate interpretation by the balance organs problematic (Eriksson et al., 2008). Fast jet operations therefore increase the likelihood of spatial disorientation, by exposing the physiological limitations of the normal human orientation systems in a dynamic motion environment. SD therefore arises from a certain perceptual interpretation of highly complex multi-sensory stimuli. It is rarely a function of a single sensory input. The increasingly demanding nature of the fast jet environment imposes ever greater cognitive and physical loads on the pilot, which may overwhelm their sensoryperceptual-cognitive abilities (Gibb et al., 2011). The ongoing prevalence of SD has led some authors to argue that ‘more research is clearly needed to understand the role of sensory integration in high workload dynamic flight operations’ (Cheung et al., 1995).

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Illusions by Phase of Flight Rather than considering each possible illusion in isolation according to which orientation system is responsible, it is arguably a more helpful approach to consider the illusions that a fast jet pilot might suffer during different phases of flight. Hence, in the following discussion a typical flight is broken down into take-off, landing and the in-flight elements in between (such as cruise, weapons delivery, air combat manoeuvring, and so on). This will help the reader to understand that at different points in the flight the fast jet pilot is at risk of various forms of disorientation, and may suffer from more than one type of illusion during a given flight. Take-off The typical take-off in a military fast jet involves significant acceleration and speed, frequently at night, and often in bad weather or other conditions of degraded visibility. In the take-off phase, the somatogravic illusion is arguably the most high-risk illusion. The somatogravic illusion (known also as the dark night take-off illusion or the pitch-up illusion) involves a particularly strong sensation of the aircraft pitching up during acceleration, such as during take-off (ATSB, 1995; Buley and Spelina, 1970; Newman, 2007). The illusion generally occurs in conditions of poor visual cues, such as during night operations or instrument meteorological conditions. During a take-off in such conditions, the otoliths will accurately register the linear acceleration produced. However, in the absence of good visual information that would confirm the actual aircraft attitude, the brain instead assumes that the linear acceleration is a pitch-up event. The pilot then almost instinctively pushes forward on the control column, in order to cancel out the sensation of too much pitch-up, and to achieve a feeling of normal pitch. This results in a pitching down of the aircraft, and since this illusion generally occurs during a low-altitude setting with take-off, the inherent risk is that the aircraft is flown into the ground. The somatogravic illusion has an onset rate of less than 1 second, and can persist for up to 30 seconds (Cheung et al., 1995). Cheung et al. (1995) in their study cited aggressive afterburner take-offs into a degraded visual environment (cloud) as leading to 2 SD accidents attributed to the somatogravic illusion. The absence of good visual cues is key to the genesis of the somatogravic illusion (Newman, 2007). Eriksson et al. (2008) used a helmetmounted display to generate synthetic good visual cues and scene flow, and was able to reduce the extent of the somatogravic illusion. The opposite form of this illusion can occur during flight when a sudden deceleration occurs in conditions of poor visual cues. The pilot may experience a strong sensation of pitching down, which may lead the pilot to inadvertently pull back on the control column in order to offset the apparent pitch down. However, the aircraft then actually pitches up, and may even stall.

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The false horizon illusion is a visual phenomenon, and while it can occur during any phase of the flight it is considered here as an after take-off event during the climb out phase. Sloping cloud banks can deceive a fast jet pilot who climbs up through a cloud layer and finds themselves on top. Under visual flight conditions, there is a strong natural tendency to use the top of the cloud bank as a horizontal reference. However, if the cloud bank is sloping, as can occur in certain meteorological conditions, the pilots may inadvertently fly relative to the cloud bank with a degree of bank in order to maintain what they perceive as straight and level flight. By orientating themselves against a false horizon such as this, keeping an accurate heading is problematic. Reference to the instruments will show the aircraft continually drifting off the intended course. All things being equal, the pilot will then discontinue use of the cloud bank as a horizontal reference and will fly straight and level relative to the aircraft instruments. However, there is potential for this situation to set up a disorientating event, particularly if the instruments fail or the pilot does not believe them (Holmes et al., 2003). In-flight Phase The in-flight operational phase of flight is where the bulk of disorientation events occur. In a Canadian study, all but two of the SD accidents occurred during this phase. Five of these accidents involved air combat manoeuvring, four involved cross-country and low-level flight (Cheung et al., 1995). A US Navy study found that 43 per cent of fast jet SD incidents happened during the in-flight phase (Bellenkes et al., 1992). More than 85 per cent of SD accidents in a USAF study occurred during the in-flight phase (Lyons et al., 2006). The leans has been recognised as the most common form of disorientation, and this is also true in fast jet operations (Cheung et al., 1995; Holmes et al., 2003, Sipes and Lessard, 2000). Fast jet pilots will almost certainly experience this form of disorientation at some point in their flying career. Fortunately, episodes of the leans are generally Type II, and relatively minor. The leans illusion is manifested by a false sensation of roll, which may cause pilots to lean to one side in order to cancel out the false sensation. The leans can occur in good visual conditions. Typical conditions for the leans involve a pilot flying straight and level, and then the aircraft enters an inadvertent turn (due to wind, for example). This turn is at a sub-threshold rate of angular acceleration for semi-circular canal activation. The pilots (who are usually head-down in the cockpit) believes that they are still straight and level, despite the turning aircraft. The pilots then recognise the inadvertent turn and undertakes immediate recovery to straight and level flight. However, the return to straight and level flight is generally made at a supra-threshold rate of angular acceleration for semi-circular canal activation. As such the first input the canals receive is when the aircraft returns to straight and level flight, and they then register an apparent change from straight and level flight to a turn in the opposite direction.

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To counter the mismatch between a straight and level aircraft attitude and a head-level sensation of roll to one side, the pilots lean in the direction of the initial turn to make their head agree with the aircraft. If this is maintained and no further movements are made, the false sensation of roll will wear off over about 30–60 seconds (Newman, 2007). The somatogyral illusion is another attitude misperception illusion (also known as the graveyard spin or spiral). During the entry into a spiral turn or a spin (deliberately or inadvertently), the semi-circular canals will register the initial supra-threshold angular acceleration. However, once the spiral turn stabilises in a constant velocity state, the angular acceleration will decay to zero. The semicircular canal input will washout, and effectively signal that there is no turn happening (Newman, 2007; Wickens et al., 2006). Normally, the dominant visual system will suppress the semi-circular canal inputs and confirm the ongoing turn, due to rotation of the outside visual world. However, in conditions of poor visual cues, the pilot may experience a sensation that they are no longer turning, owing to the decay of vestibular rotation information. When the pilot recovers from the turn to a straight and level attitude, the semi-circular canals register the change in angular velocity associated with the cessation of turning. This can then create an illusory sense of counter-rotation in the opposite direction to the original turn. This strong sense of counter-rotation may lead, in the absence of good visual cues, to a re-entry into the original turn (Newman, 2007). This will cancel out the illusory counter-rotation for the pilots, but despite feeling straight and level they are back in the original turn and descending. Tightening the turn can also exacerbate the false sense of rotation. Unless this is recognised and appropriate recovery action taken, the aircraft will eventually impact the ground. There is one further complication, based on the close connection between the visual and vestibular systems. Upon recovery from the prolonged spiral turn, the illusory counter-rotation input can then lead to a series of involuntary oscillatory eye movements known as nystagmus. This leads to movement of the visual field, which reinforces the false sense of counter-rotation. The pilot gets apparently confirmatory visual evidence of rotation, which leads the pilot to re-enter the original turn. The nystagmus decays quite quickly, which then allows the pilot to see clearly that the original turn has been re-entered. The pilot may then recover, but in so doing then gets the illusory sense of rotation again, and succumbs to the illusion all over again. This cycle of illusion-recovery-illusion, if not broken by clear action from the pilot, can lead to ground impact. The potential for this illusion to lead to Type III SD is clear. The pilot can become confused and lose control of the aircraft. The Coriolis illusion is a severe tumbling sensation, often of rapid onset, brought on by moving the head out of the plane of rotation, simultaneously stimulating one set of semi-circular canals and deactivating another set (crosscoupled stimulation). The tumbling can be severe enough to cause nausea. The

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Coriolis illusion has been described as the most dangerous vestibular illusion (Gillingham, 1992). The illusion results when a pilot moves their head in a different plane of rotation from the aircraft which is in a turn. The canals in the plane of rotation of the aircraft signal the angular acceleration, but the other two sets of canals, sitting in different axes, will not signal anything. The pilot’s head movement (owing to looking back into the turn, for example), leads to cross-coupled stimulation of the semi-circular canals. The set of canals that were originally signalling the turn are now taken out of the plane of rotation of the turn, and signal a deceleration. Simultaneously, a new set of canals is brought into this plane of rotation owing to the head movement, and these canals signal acceleration. The brain then receives two sets of contradictory inputs (acceleration and deceleration). The result is a complex series of strong and disorientating tumbling movements being experienced by the pilot. The degree of tumbling sensation is a function of the magnitude of the initial turn and the direction and speed of head movement (Newman, 2007). The G-excess illusion is a potentially very dangerous illusion, especially if it occurs during low-altitude, high-speed operations, such as an attack mission or weapons delivery profile (Ercoline et al., 2000). In such settings, the illusion can lead to erroneous control inputs which can be disastrous given the limited time available to recognise and recover from the illusion. The G-excess illusion is a complicated phenomenon, involving multiple inputs to the vestibular system with limited visual input. In simple terms, the illusion leads to a false sense of underbank during a turn at more than +1 Gz when the pilot looks back inside the turn (and hence loses sight of the horizon). This situation may occur after weapon delivery, when the aircraft pulls up and rolls during the egress phase, allowing the pilot to look back at the intended target to check the results. If such a maneuver is performed at +2 Gz, the pilot may experience an apparent underbank of at least 10 to 20°. In order to maintain the desired bank angle, the pilot may apply more bank, with the unintended consequence being a significant overbank (which may be more than 100°). This can then result in a rapid downward trajectory with dramatic loss of altitude from a relatively low initial altitude, which can lead to ground impact if the situation is not recognised and recovered from quickly. Altitude misperceptions can be disastrous to a fast jet pilot. This type of misperception is associated with flight over featureless terrain (such as large bodies of water, snow, frozen lakes, desert, and so on) often in poor or degraded visual conditions where contrast levels are low (Cheung et al., 1995; Newman, 2007). The danger with this illusion is that the fast jet pilot will fly too low, leading to controlled flight into terrain. At low level, the passage of detailed information in the pilot’s field of view gives a good sense of height above ground level. This visual information is not available over featureless terrain, since contrast and shadows may not be present to give the pilot a sense of ground proximity. Low light conditions and poor weather make this even more problematic, as does turning flight at low level

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(where peripheral visual cues may be lost). Tactical considerations can make this misperception more likely for certain mission types. High levels of manoeuvring due to weapons delivery, low-level air combat manoeuvring, guns jinking and other defensive manoeuvres all increase the pilot’s workload. This high workload can lead to channelised attention and a restricted effective field of view owing to task saturation. This can increase the potential for height misperception over featureless terrain. In a Canadian study, Cheung et al. (1995) reported three fatal fast jet SD accidents due to height misperception over smooth terrain. The lack of visual orientation cues owing to absence of shadows and low contrast levels were considered contributory, as was channelised attention in one case. Dissociative illusions are a function of the central integration of sensory inputs, depending on the prevailing circumstances. These illusions can result in unusual (and infrequent) forms of SD such as the ‘Break-off’ illusion, the ‘Knife-edge’ illusion and the ‘Giant hand’ illusions. The break-off illusion is associated with feelings of unreality and detachment from the environment (Newman, 2007). In some cases, the pilots may feel that they are sitting out on the wing of their aircraft, watching themselves flying the aircraft. The knife-edge and giant hand illusions are both related to a false sense of aircraft movement and operability, but are opposite to each other. The knifeedge illusion gives the pilot a sensation that the aircraft is inordinately sensitive to control inputs and finely balanced in the air. The giant hand illusion gives the pilot the opposite sensation, that the aircraft is effectively fixed in the air and resistant to control inputs. These illusions (all variations on a common theme) are generally associated with high-altitude flight where the pilot has relatively few cognitive demands (such as during an autopilot-controlled transit flight). Landing The landing phase does not lead to as many instances of SD as the take-off or in-flight phases. In Canada, Cheung et al. (1995) reported no SD incidents in the landing phase. A US Navy study found that landing was associated with only 22 per cent of fast jet SD incidents (Bellenkes et al., 1992). The false horizon illusion can potentially affect a pilot during a night approach to landing, particularly if approaching a ground feature at an angle. This might consist of a coastal highway with lights, where the line of lights may lead the pilot to use it as a substitute visual horizon. Since the flight path of the aircraft is at an angle to the line of lights, using it as a horizontal reference will see the aircraft in a variably banked attitude. If unrecognised, this can lead to an undetected descent that could result in ground impact. The blackhole approach has resulted in several SD accidents over the years. This illusion involves a night approach to land where there are no visual references between the aircraft and its intended runway – a visual ‘blackhole’. The absence of peripheral visual cues, especially below the aircraft, can lead the pilot to fly a

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constant visual angle with the runway during the approach. This results in a curved flight path, with an initially steep descent progressively flattening out into a much lower than normal approach. The aircraft may land short of the runway or impact terrain if the illusion is not adequately recognised. At the very least, an unstable approach path might result. Runway shape and slope illusions can also sometimes occur on landing, particularly when a visual approach is made. Use of instrument landing systems and other guidance systems make these less likely, but the potential remains for them to occur and surprise a pilot. An approach to a down-sloping runway means that at a certain altitude and distance from the runway, less will be seen of the runway compared with a normal, completely flat runway. If the pilot is unaware that the runway is down-sloping, the pilot may perceive that they are low on approach, and thus gain height to make the runway look like it should at that height and distance. However, the unsuspecting pilot is now too high, will likely fly a less stable approach and land well down the runway, and possibly face insufficient stopping distance. The exact opposite may occur if the runway is upsloping, leading to a landing short of the runway. The width and length of the runway can similarly trick an unsuspecting pilot. A wider than usual runway may make them feel lower and closer, making them fly higher than normal. Conversely, a narrower runway may make them feel further away and higher than normal, making them fly lower. Longer than usual runways give an illusion of being too high, and shorter than usual runways give an illusion of being too low. Risk Factors Several factors help contribute to a spatial disorientation event. Broadly speaking, these factors can be grouped into three distinct (yet overlapping) sets: pilot, aircraft and operational factors. Some of these factors are clearly a function of flight (for example, night time operations, poor weather) but others (such as pilots flying while unwell) can and should be addressed prior to flight in order to minimise the likelihood of spatial disorientation. Pilot Factors Various factors can affect pilot performance during flight. These include illness, medications of various types, alcohol and fatigue (Gibbons, 1988; Guedry et al., 1975; Levett and Hoeft, 1977; Modell and Mountz, 1990; Newman, 2004; Ryback and Dowd, 1970). These factors can functionally impair the performance of the sensory systems, as well as the brain’s ability to process and integrate orientation information (Burton and Jaggars, 1974; Gilson et al., 1972; Katoh, 1988; Levett and Karras, 1977; Oosterveld, 1970; Schroeder, 1971; Schroeder et al., 1973). This is likely to increase the risk of disorientation in the three-dimensional flight

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environment. From this perspective, it is clear that fast jet pilots should not fly when not physically and mentally well, as doing so only serves to increase their chances of succumbing to SD. It is important to remember that experience does not protect a pilot from spatial disorientation (Gibb et al., 2011; Holmes et al., 2003; Lyons et al., 1994; Newman, 2007; Wickens et al., 2006). In a Canadian SD study, the average total flight time and time on type for pilots experiencing SD were1950 hours and 775 hours, respectively (Cheung et al., 1995). SD can affect any pilot, anytime, anywhere, in any aircraft, on any flight, depending on the prevailing circumstances (Newman, 2007). While previous experience of SD does not mean that it cannot be experienced again, it does seem to allow the disorientation phenomenon to be recognised more readily in the future (Holmes et al., 2003). Aircraft Factors Several aircraft factors can contribute to spatial disorientation. Single-pilot fast jet aircraft are arguably more likely to experience disorientation, as the single plot has no other person to check information with, or to hand over control to if disorientation occurs. An autopilot system will allow a disoriented fast jet pilot to maintain safe flight even while disoriented if the autopilot is engaged. This may allow a disoriented fast jet pilot to overcome their erroneous sensations while the aircraft’s fate is not threatened by their SD-induced inappropriate control inputs (Newman, 2007). Some authors have advocated the development and introduction into service of automatic ground collision avoidance systems (Auto-GCAS) to prevent SD-induced controlled flight into terrain (Lyons et al., 2006). The design of cockpits, the layout of instruments and the presentation of flightcritical information are important in creating a user-friendly and disorientationresistant environment for the pilot. Information displayed on aircraft instruments should be easily interpretable and non-ambiguous, and should not be overwhelming in terms of the perceptual and cognitive load imposed on the pilot. The instrumentation should present clear and intuitive attitude and position sense, which the pilot under conditions of high workload can use to rapidly build a model of what the aircraft is doing. Advanced fast jet cockpits, with their enhanced information processing and presentation capabilities, have increased the perceptual and cognitive workload of pilots. Head-up displays (HUD) are designed to give flight-critical information to the fast jet pilot while they are looking ahead of the aircraft. However, there is evidence that SD phenomena due to HUD use occur in fast jet pilots (Holmes et al., 2003). While helmet-mounted displays increase viewing opportunities for the pilot and are designed to improve situational awareness, some authors have suggested that they can overwhelm the pilot’s orientation system with sensoryperception-cognitive mismatches between the various sensory inputs, leading to increased likelihood of SD (Gibb et al., 2011). The technology generates new

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threats to the pilot, such as visual clutter, cognitive tunnelling and task saturation, which can all help to induce SD. Increasingly, fast jet pilots are using vision enhancement devices during flight, including night vision goggles (NVG). While these devices tend to increase the information available to a pilot, they can potentially increase the chances of disorientation. NVGs have a significantly reduced field of view (40°) and a monochromatic display. In a UK study, 48 per cent of respondents had experienced spatial disorientation associated with NVG use (Holmes et al., 2003). Most of the fast jet pilots in this study were not NVG users, however. Nonetheless, in fast jet pilots using NVGs the potential for SD is clear. Part of the problem is the apparent increase in pilot confidence the technology can lead to, despite its inherent limitations (Gibb et al., 2011). Operational Factors According to a USAF study, the chance of being involved in a significant fast jet accident owing to SD was seven times higher at night than during day operations, and three times higher in IMC than in non-IMC operations (Sundstrom, 2004). The absence of good visual cues during flight at night and/or in bad weather makes SD much more likely. Developing a mental model of orientation based on information from the flight instruments might take place while false information is being sent to the brain from the vestibular and proprioceptive systems. In a US Navy study, for all phases of flight, 52 per cent of fast jet SD occurrences involved night operations (Bellenkes et al., 1992). The very nature of fast jet operations increases the potential for SD. Highspeed, low-level operations, or air combat manoeuvring with high +Gz exposure, all pose challenges for the orientation system of the pilot, especially when coupled with the high perceptual and cognitive demands of the mission itself. The increased agility of the modern fast jet has been cited as a contributory factor in the elevated SD rate in fast jet pilots (Gillingham, 1992). Countermeasures A significant effort has been mounted around the world over many years to mitigate the risks of SD and prevent the loss of pilots and aircraft (Gibb et al., 2011). The various countermeasures that have been developed can be grouped into either pilot training approaches or technology approaches. Training Spatial disorientation awareness training is a regular part of a fast jet pilot’s training in the vast majority of air forces. In many cases it is conducted as part of general aviation medicine and human factors refresher training. There is evidence

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that such training increases the likelihood that a fast jet pilot will recognise an inflight situation as due to disorientation and thereby reduce the chance that the pilot will succumb to an illusion (Holmes et al., 2003). The ground-based component of this training (common to most air forces) teaches fast jet aircrew about the normal orientation process and the various illusions that can be experienced in different phases of flight. Some authors have stressed the need to focus on the in-flight phase for fast jet pilots, where most SD events occur (Lyons et al., 2006). In many air forces, specialised ground-based simulators are used, to give fast jet aircrew a demonstration of what these illusions look and feel like. The Indian Air Force has reported on its results with dedicated SD simulators and found that over 90 per cent of pilots found the training was beneficial, and that it promoted faith in their instruments and an ability to safely recover from SD events (Baijal et al., 2006). This training is discussed further in Chapter 8. In-flight SD training is given to aircrew in some air forces (Holmes et al., 2003). This training is designed to give aircrew techniques to recognise or overcome SD illusions, such as believing the information presented by the flight instruments, procedures for inadvertent entry into bad weather (instrument meteorological conditions, IMC) and recovery from unusual attitudes. Additionally, it is wise for fast jet pilots to receive training in pre-flight planning for SD. Fast jet pilots should consider the potential for disorientation to occur at different stages of their flight, especially when the nature of their intended mission and the ambient weather conditions are taken into account. This pre-flight preparation can help the fast jet pilot to recognise SD in-flight if it occurs and avoid its disastrous outcomes (Newman, 2007). Technology Various technological measures have been looked at to help fast jet pilots with SD recognition and recovery, beyond simply improving the display of flight information and enhancing cockpit design. Many of these systems are not yet operational, but have received some research attention. Efforts have been made to develop pilot-in-the-loop (or cognitive cockpit) systems that take various biological signals (such as cardiovascular parameters) from the pilot as markers of physiological stress and integrate them into the aircraft’s systems, in order to improve life support equipment function (Cheung and Hofer, 2003). Some authors have suggested that the use of such systems could potentially help as a countermeasure for SD, although the concept is far from mature and reliable (Cheung et al. 2004; Forster, 1998; Westmoreland et al., 2007). Another concept developed is the Tactile Situation Awareness System (TSAS), which is a vest embedded with tactile stimulators that give the pilot a correct sense of orientation with respect to the gravitational vertical (Rupert, 2000). It has been successfully flight tested, but not yet fielded operationally.

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Case Study On 28 March 2012, an F-15E Strike Eagle of the 391st Expeditionary Fighter Squadron was involved in a 27-aircraft strike package, as part of a large exercise in the South-West Asia theatre of operations. The aircraft was the lead of a formation of two F-15E aircraft within the overall package. After the tactical part of the mission had been completed, the crew removed their night vision goggles and flew back to their base. There was significantly reduced visibility in the area, owing to atmospheric dust and an indistinct horizon. The pilot is believed to have incorrectly orientated himself with respect to the outside visual scene, and began progressively making abrupt flight manoeuvres. The aircraft ended up in an adverse attitude, inverted at 1,800 feet above ground level and in a 25-degree dive. The weapons systems officer (WSO) in the back seat determined that the front-seat pilot was disoriented and took control of the aircraft. After attempting to recover, the WSO initiated the command ejection sequence for both crew. The WSO ejected safely with minor injuries, but the pilot was fatally injured. The pilot successfully ejected from the aircraft but impacted a 377-foot telecommunications tower after leaving the aircraft. The aircraft impacted the ground approximately 18 miles west of its deployed base and was destroyed. The accident investigation report determined that the pilot was spatially disoriented as a result of a visual illusion during a low-visibility approach to land at night. Lack of an effective instrument cross-check by the pilot and the ambient environmental conditions were cited as contributory to the accident.

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Chapter 5

Life Support Equipment In earlier chapters of this book, the complex and challenging nature of the fast jet operating environment has been highlighted. This environment consists of a number of potential risks to the fast jet pilot, such as hypoxia, spatial disorientation, G-induced loss of consciousness and ejection, among others. To combat these risks to survival and well-being, the modern fast jet pilot is supplied with a range of life support equipment. Much of this is integral to the aircraft, such as the oxygen and cockpit pressurisation systems, the anti-G system and the ejection seat. However, the fast jet pilot also must wear a number of items of life support equipment, and it is this pilot-centred equipment that forms the main focus of this chapter. The fast jet pilot must wear specific equipment for self-protection in the aircraft. This equipment usually consists of the flight suit, a flight helmet, an oxygen mask, a G-suit, and a survival vest. In addition, depending on the mission requirements, the fast jet pilot may also need to wear an immersion suit, a liquid cooling garment and/or a chemical, biological, radiological and nuclear (CBRN) protection ensemble. These items of equipment will be briefly discussed in this chapter. The aim is to highlight the complexity of the fast jet operating environment by emphasising the large amount of life support equipment required. This equipment, while protecting the pilot, can also cause additional issues and limitations, such as thermal loading, movement restriction and effects on comfort. To minimise these, aircrew equipment integration is an important process, which in addition to anthropometry will be discussed as well in this chapter. The Flight Suit The flight suit effectively represents the base layer of clothing for the fast jet pilot (in combination with suitable underwear, which may of course be thermal in nature). Together with the flight suit, the fast jet pilot will wear flying boots and flying gloves, which do not require much further elaboration here. The flight suit is designed to be of a comfortable fit, and can either be a generalpurpose weight, or available in summer and winter weights. Most military flight suits are common across all platforms, and as such have multiple adjustments and pockets. They may be supplied in a typical drab olive-green colour, or have specific camouflage patterning. The choice of colour and pattern is very much dependent on the needs of the Service and the type of mission being undertaken. The range of possible options is clearly large.

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66 Helmet/Visors

Life Preserver

Flight Suit

Survival Kit

G-Suit

Oxygen Mask

Oxygen Hose

Chest Counterpressure Garment

Flying Gloves

G-Suit Connector Hose

Flying Boots

Figure 5.1 Life support equipment as worn by a fast jet pilot The key aspect of the military flight suit is that it is generally constructed out of a flame-resistant material. Usually this is a product known as Nomex (a trademark of the DuPont Corporation), which is an aramid polymer fibre with impressive flameresistant properties. It can withstand temperatures in excess of 1,000°C, without melting, and the thermal resistance properties do not deteriorate with frequent laundering. Such materials provide reliable thermal protection in a comfortable flight suit, and as a result almost all fast jet pilots around the world today will be using a Nomex-based flight suit. The Flight Helmet The flight helmet is probably the most technologically sophisticated aspect of a fast jet pilot’s life support equipment. The helmet has evolved considerably from its earliest versions, when it was often made out of leather and also often adopted from various sports. The modern fast jet helmet performs a variety of important functions, such as impact protection, communications and attachment for the

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oxygen mask assembly. In addition, the helmet is now increasingly being used to mount a variety of SA-enabling devices such as night vision goggles, sighting and display systems and weapons cueing systems. The basic features and requirements of a flight helmet are that it should be as lightweight as possible, as comfortable as possible and as easy to fit as possible, while offering as much impact protection as possible. It must also not adversely affect the centre of gravity of the pilot’s head, and not restrict the pilot’s peripheral vision. It must also have a degree of inherent stability when worn, such that the helmet remains in position despite +Gz loads and head movements. It must also provide a high level of noise attenuation and hearing protection. The flight helmet typically consists of a hard outer shell, which is often made from advanced materials such as fibreglass, Kevlar (an aramid polymer like Nomex but with characteristics giving it high levels of strength) or composite materials. The helmet usually includes a soft edge roll, which covers the periphery of the outer shell. This helps makes the helmet more comfortable and eliminates sharp edges. The outer shell also has the polycarbonate visors attached to it. These visors (usually a dark tinted one and an additional clear one) are attached via elastic straps, such that the pilot can manually pull them down onto the face as required. These visors help protect against windblast and facial or eye damage, as well as providing some glare protection when the tinted visor is used. They typically block 99 per cent of ultra-violet (UV) light from penetrating the visor. In certain circumstances, other visors can be added or substituted, for purposes such as laser protection or to improve contrast sensitivity. The hard shell also contains the oxygen mask attachment points. For impact protection, there is an energy absorbing layer, often made out of specifically moulded polystyrene foam or similar compounds. This layer performs most of the work of absorbing impact energy, and distributing it across a wide area for maximum protection. The innermost layer is the layer that is in contact with the pilot’s head. This is usually a thermoplastic liner, which is detachable and often moulded specifically for a particular pilot’s head. This allows for maximum comfort, as the helmet is effectively anatomically correct for the contours of the pilot’s head. The communication system consists of ear cups with integrated speakers, which combine with the microphone contained in the oxygen mask (see later section) to give the pilot hearing and speech functions. The ear cups tend to be insulated and equipped with edge seals (often gel-filled) for improved noise attenuation capability. The end result of these various layers and items of equipment is a helmet with an overall weight of 1 to 2 kg. This is an impressive achievement, given what the helmet is asked to do in the modern context, and is largely due to significant improvements in materials technology. As an example, a common helmet used by many fast jet crews around the world is the HGU-55/P (manufactured by the Gentex Corporation). This weighs just over 1 kg (helmet alone). Even the extralarge size of this helmet weighs only 1.126 kg.

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A helmet must be correctly sized and fitted to the pilot for it to function optimally. A poorly fitting helmet can cause a number of problems, such as fatigue, discomfort (so-called ‘hot spots’ where a specific area of the head causes pain), reduced ability to use the helmet-mounted equipment (see later section) and also reduced impact protection. Indeed, a poorly fitted helmet which can move easily relative to the head of the pilot may cause more injuries than it prevents during impact and/or ejection. Impact Protection As mentioned previously, one of the most important reasons for a fast jet pilot to wear a flight helmet is to reduce the risk of head injury. Such injuries might conceivably occur during impact with the ground while still sitting in the cockpit. However, the high-speed nature of such an impact tends to be unsurvivable, thus somewhat negating the point of wearing a helmet. In the fast jet environment, the greatest risks to the head occur during ejection (owing to the violent nature of aircraft egress with an ejection seat, and the associated effects of windblast), as well as in the event of bird-strike while in-flight (particularly where the bird penetrates the canopy and potentially strikes the head of the pilot). In addition, the somewhat unpredictable nature of the parachute landing following ejection means that a helmet can considerably reduce the risk to the head of injury. Helmets used for the protection of flight personnel must satisfy an appropriate standard. ANSI Z-90 is a generalised standard that sets out the requirements for protective headgear including helmets. This standard sets out the testing requirements for a helmet, in terms of assessing its impact attenuation (to prevent excessive acceleration being imposed on the head) and penetration resistance (to prevent penetrating injury of the head). In the United States, Military Standard MIL-H-87174 is a variation of the ANSI standard that examines military flight helmets specifically. In general, impact protection is achieved by the energy absorption layer of the helmet compressing to around 40 per cent of its original thickness on impact. This compression absorbs the impact force, but moreover it distributes the force over a wide area throughout this helmet layer, thus reducing the force per unit area imparted to the head (compared with a single point of impact with no helmet). The end result of this is that the total acceleration imparted to the head on impact should be less than 400 G, when tested using the approved methodologies in the appropriate standard. In terms of penetration resistance, helmets should not show penetration when a specific weight (1.5 kg) is dropped from a height of 1.5 metres (according to the European standard). The helmet must also be able to be retained during impact or windblast exposure, without breaking or stretching of the chinstrap or nape strap assembly. According to MIL-H-87174, the helmet must not detach from the head, or become loose or break, during exposure to windblast velocities of 450 knots. In some cases, the helmet can be optimised for potential high-speed (even supersonic)

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ejections. Some Russian fast jet helmets have frontal air holes designed to channel high-speed air through the helmet and in so doing prevent the helmet generating sufficient aerodynamic lift which it would otherwise do. Such lift could forcibly separate the helmet from the pilots’ head during high-speed ejections, and even seriously injure or kill the pilot if the chinstrap held fast while the helmet lifted away at high-speed. Helmet-Mounted Sighting and Display Systems Helmet-mounted sighting and display systems will be extensively discussed in Chapter 6 in terms of their SA-enabling capabilities. These systems are increasingly being used to help meet the mission requirements of the fast jet pilot. However, as Chapter 6 demonstrates, these systems are not without their human factors challenges. The widespread use of the helmet as a mounting platform for sighting and display systems has a number of issues associated with it. These include the additional weight and centre of gravity shifts imposed on the head and neck of the pilot, as well as altering the dynamics and potential injury consequences of ejection. Impact protection is also an additional concern. There are several impact protection and biodynamic issues to deal with (Newman, 2002; 2006). Impact protection must not be diminished by the extra demands of the sensor package and its integration into the helmet. The distribution of cables and electronic elements in the helmet should not adversely affect the impact force attenuation characteristics of the energy absorption layer. Additionally, the helmet-mounted equipment should not create adverse torsional or rotational accelerations on the head and neck of the pilot due to the mass of the equipment and/or its location relative to the centre of gravity of the head-helmet complex. A forward-located centre of gravity is also problematic for the pilot, in terms of neck muscle fatigue and potential neck injury. Making the helmets lighter helps considerably, but the additional weight of the helmet-mounted equipment can obviate any improvements to the standard helmet weight. The standard HGU-55/P fast jet helmet, visor and communication combination weighs approximately 1.7 kg. The addition of the Joint HelmetMounted Cueing System (JHMCS) to this helmet adds another 0.5 kilogram to the total (Lange, 2011), which under +9 Gz is an effective additional weight of 4.5 kg. Night vision goggles (NVG) can add 0.7 kg to the total helmet weight. Given an average head weight of around 5 kg, the head-helmet-JHMCS combination weighs around 7.2 kg at +1 Gz, and 64.8 kg at +9 Gz. This represents a significant additional weight for the neck to deal with, particularly during air combat manoeuvring. Despite all the technological improvements and advanced materials being used, neck injuries remain a very common occupational injury for fast jet pilots. A recent Royal Danish Air Force study examined neck injury prevalence in F-16 pilots using the JHMCS (Lange et al., 2011). The authors found that 97 per cent of the pilots experienced neck pain either during flight or immediately afterwards.

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Furthermore, the authors highlighted what they regarded as two conflicting goals in this fast jet population: the requirement to keep the head still while under high +Gz (to limit the potential for neck injury), and the requirement to move the head frequently and abruptly to fully exploit the JHMCS technology (thus potentially increasing the potential for neck injury).The increasing demands being made of helmets as mounting platforms for mission-critical equipment are thus unlikely to reduce the magnitude of this problem in the immediate future. Some manufacturers are developing modular helmets, which consist of an inner individually custom-fitted crash protection module and an outer sighting and display module integrated with and configured for whatever helmet-mounted sensor systems an end-user customer might require. It is hoped that such design enhancements might help to reduce the rate of neck injury in fast jet pilots. One of the practical issues with helmet-mounted sighting and display systems is the requirement to ensure that the helmet fits correctly. A poorly fitting helmet will interfere with the ability of the wearer to accurately use the helmet-mounted display and sighting system (particularly if they are forward-positioned night vision goggles). If the relative eye position is crucial for the proper use of the display system, then a poorly fitting helmet will adversely affect this. Stability of the visual image is dependent on the helmet maintaining a stable position on the head of the wearer, despite any head movements and high +Gz loads due to manoeuvring. Relative movement of the head and helmet will lead to increased difficulties using the helmet-mounted sighting and display system. Advanced Helmet Design Options There are some design innovations that are worthy of brief mention here. Flight helmets are increasingly being made as ‘snag-free’ as possible. This is important, as protuberances on the outer layer could potentially lead to the pilot’s head getting stuck in the cockpit, perhaps wedged between the ejection seat head-box and the canopy or other cockpit structures. Additionally, anti-snag fittings are important during the ejection process, as parachute risers getting tangled in the helmet fittings could be catastrophic, and turn a potentially survivable ejection into a lethal outcome. Positive pressure breathing for G protection (PBG) was discussed in Chapter 3. The USAF’s Combat Edge PBG system incorporates a bladder in the back of the HGU-55/P helmet, between the thermoplastic liner and the energy absorption layer. This bladder inflates automatically with the application of PBG pressure, and is designed to ensure a good oxygen mask seal under high incoming pressure at high +Gz levels.

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The Oxygen Mask The oxygen mask is a crucial item of life support equipment for the fast jet pilot. It functions as the final piece of the delivery system for breathing air and emergency oxygen. It also performs a vital aspect of the communication function, as the oxygen mask typically incorporates the microphone element. Since the fast jet pilot wears the oxygen mask at all times during the flight, the mask also provides some face protection during ejection and windblast exposure, as well as against traumatic injuries such as bird-strike. The oxygen mask as a minimum covers the face from the bridge of the nose to the lower part of the chin, and laterally covers both cheeks. Some masks wrap more completely around the face, with the lower edge extending under the chin. The typical oxygen mask fits to the helmet via a series of attachment points, located on the sides of the helmet. Different countries and helmet manufacturers use different helmet mounting systems (bayonet-style connectors are common), but in general they all tend to have universal characteristics such as ease of attachment and the ability for quick release. Of primary importance is a good fit. The mask will be worn for an extended period of time, so a good comfortable fit on the face is essential. In addition, a good mask fit should create a good seal with the skin of the face. This will prevent leakage of air, which can be detrimental for hypoxia prevention and G protection (especially where this involves positive pressure). A reflected edge seal is usually part of the standard oxygen mask, which creates a thin flap of silicone or rubber material inside the mask and in contact with the skin of the face. The reflected edge avoids an otherwise sharp edge being applied directly to the face, and the normal slight overpressure of delivered air will help seat the reflected small flap of the mask on to the face and establish a good seal. Most oxygen masks have an additional tensioning capability (such as the RAF P/Q mask’s so-called ‘toggle down’ option) to quickly tighten mask tension on the face to ensure a good seal when positive pressure breathing is required or when ejection is carried out. In some mask types, simply pushing the bayonet connectors further in to their attachment points will improve mask tension on the face. In an ejection situation, a properly fitted and tensioned mask will help protect the face and also help retain the helmet on the pilot’s head. The typical fast jet oxygen mask consists of a flexible rubber or silicone inner layer that attaches to the face, with a hard outer layer (known as the exoskeleton) for structural integrity and strength, as well as securing the helmet-attachment system. This outer shell is usually made from rigid plastic. The oxygen delivery hose attaches either directly in front of or below the mask, sometimes with a lateral offset if attached below. The microphone is usually inside the flexible layer, directly in front of the mouth. There is an inlet port and an outlet port for inspired air and expired air, respectively, although some masks may use a combined valve. The oxygen hose is part of the mask assembly, and contains a fitting at the end appropriate for the particular aircraft’s breathing regulator (whether this is chest-

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mounted, seat-mounted or aircraft-mounted). The hose incorporates an anti-stretch cord and has a crush-proof shape to help preserve its integrity. In the fast jet environment, the oxygen mask is of the pressure-demand variety. When the pilot takes a breath in, the non-return inlet valve opens and air is drawn into the lungs. Breathing out closes the inlet valve and opens the outlet valve, such that the expired air is dumped outboard of the mask. The opening pressures of the inlet and outlet valves need to be set in such a combination that the work of breathing is minimised. This helps to ensure that breathing with the mask in place is comfortable and natural for the pilot. Furthermore, for pressure breathing requirements, the expiratory valve needs to be loaded such that it will not open at the positive pressure levels being delivered to the mask. To achieve this, the expiratory valve is compensated. This means that the inlet pressure sent to the mask is also sent to the downstream side of the expiratory valve, which prevents it from opening due to the high positive pressure in the mask cavity. The slightly higher mask pressure generated by normal expiration is sufficient to open the outlet valve. The combination of a non-return inlet valve and a compensated outlet valve ensures the appropriate flow of breathing gas, as well as a constant expiration pressure for opening of the outlet valve. Both the work of breathing and the potential for inadvertent breathing of cockpit air are also minimised. The G-Suit As discussed in Chapter 3, the standard G-suit is worn as a pair of trousers, in effect, over the flight suit. The G-suit’s five internal bladders compress the lower abdomen, both thighs and both calves. The non-distensible fabric cover is usually made of flame-resistant material such as Nomex. Originally developed for the US Air Force, the CSU-13B/P G-suit has become a standard item of life support equipment for the fast jet pilot in many Western countries. The standard G-suit provides in the order of about +1 to +1.5 Gz protection when perfectly fitted.The G-suit does have some limitations. It is reasonably uncomfortable by its very nature, especially the abdominal bladder which can produce a significant degree of discomfort at high G levels. This has led to some pilots opting to not plug their G-suits in, preferring to accept a lower G tolerance rather than experience the attendant discomfort (Alvim, 1995; Johanson and Pheeny, 1988). New G-suit technology essentially represents a variation on a theme. Many countries have developed new generation G-suits. While they have some inherent design differences, all of these new G-suits have one thing in common: they all rely on extended bladder coverage. While the standard suit (such as the CSU13B/P or the CSU-15 A/P as used in the US Navy) covers somewhere in the region of 30 per cent of the lower body, the various advanced technology G-suits provide coverage of around 80–90 per cent (Buick, 1992; Goodman et al., 1993; Morgan et al., 1993; Ossard et al., 1995; Paul, 1996). They are thus a more complete lower-

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body garment than existing G-suits. The bladder system of a typical advanced technology G-suit wraps almost completely around the thighs and calves, and in some cases has an augmented abdominal bladder. There are several different versions of extended coverage G-suits in existence. The USAF has its Advanced Technology Anti-G Suit (ATAGS) which is part of a wider integrated life support system known as Combat Edge (Combined Advanced Technology Enhanced Design Anti-G Ensemble). The US Navy has its own version of this suit, known as the Eagle G-suit. The Royal Air Force version is known as the Full Coverage Anti-G Trouser (FCAGT) for the Eurofighter Typhoon aircraft. The Swedish Air Force’s Extended Coverage G-Suit (ECGS) also has extended bladder coverage. STING is the name for the advanced technology G protective system developed by the Canadian Forces, and consists of an extended coverage G-suit and a positive pressure breathing system (similar to the USAF’s Combat Edge). The French Air Force’s ARZ 830 system is an extended coverage G-suit which is coupled with an electronically controlled anti-G valve, and is standard equipment in the Dassault Rafale advanced tactical fighter (Ossard et al., 1995). An extended coverage G-suit provides approximately twice the G protection of a standard G-suit. This represents a significant improvement in the level of protection against G-LOC for the fighter pilot. Chest Counterpressure Garment As mentioned above, several extended coverage G-suit systems are used in combination with pressure breathing for G protection (PBG). A key element of this system is the use of a chest counterpressure garment (CCPG). This is usually a sleeveless vest, with an outer layer of flame-resistant material such as Nomex and an internal inflatable bladder. The vest inflates with pressurised air supplied by the anti-G valve system. It inflates to the same pressure as supplied to the lungs via the PBG system. The chest counterpressure garment is intended to prevent over-distension of the lungs due to pressurised breathing air, and to balance the pressures across the lung wall (so that the pressure inside the chest is equal to the pressure outside the chest). This latter point is an important one. Any differential in pressure between inside and outside the chest will be translated into difficulty and discomfort with the normal breathing cycle. To a pilot this will mean difficulty breathing out (when chest pressure exceeds CCPG pressure), and breathing in (when CCPG pressure exceeds chest pressure). By keeping the transchest pressure equal, the work of breathing is normalised and the pilot is able to breathe in an essentially normal manner, despite the potentially high breathing pressures (up to 60 mmHg at a +Gz load of +9 Gz). There is some evidence that the increased weight of the chest wall itself under high +Gz loads will provide a natural counterpressure effect, such that a specific counterpressure garment may not be needed (Balldin et al., 2005; Grönkvist et al., 2005).

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One emerging physiological problem that has been found to be associated with the use of positive pressure breathing is arm pain, which can be significant (Green, 1997; Linde and Balldin, 1998; Watkins et al., 1998). An effective solution to this problem remains elusive. The Survival Vest The survival vest is a chest garment worn over the flight suit that incorporates an inflatable life preserver and pockets for various survival aids. The life preserver is fitted as a low-profile stole that passes around the back of the neck and on to the front of the chest. It is generally of lightweight construction, using flameresistant materials such as Nomex, and the design of the vest is such that it offers little restriction of movement (important in a survival situation, especially in water). There are various adjustment straps and fittings, and in some cases lifting harnesses are incorporated to assist with subsequent helicopter retrieval. There is also usually a whistle, and a buddy-line to secure two or more people together in the water. On contact with water, the life preserver automatically inflates via an integrated carbon dioxide gas canister. In some cases there are two inflatable chambers for redundancy purposes, such that damage to one will not hinder the floatation capability of the other. The survival aids contained depend on the requirements of the mission and the Service operating the aircraft. Much potential choice exists, but in general one pocket will contain a personal radio transceiver. The majority of the survival equipment that might be need by a fast jet pilot following escape from the aircraft is contained within the personal survival pack fitted to the ejection seat. The Immersion Suit In circumstances where flight over water is an integral part of the mission, fast jet crews may also need to wear an immersion suit. In general, this is effectively a dry suit worn over the other clothing layers. The purpose of the immersion suit is to protect the pilot from the extreme physiological hazards associated with cold water immersion, such as hypothermia. The modern immersion suit is a lightweight coverall. The suit includes wrist and neck seals, and integrated socks for wear inside the flying boots. Zips allow the suit to be opened up if physical activity warrants removal of trapped heat. The suits are designed to offer an acceptable compromise between immersion protection and mobility in the cockpit. They are usually made of a lightweight, specialised material that is waterproof as well as ventile. The ventile aspect allows moisture to be wicked away from the body, thus prevent overheating and sweating inside the suit. If this did not occur, heat build-up and sweating would create

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creating a damp internal atmosphere inside the suit and significantly reduce its thermal protective abilities. The immersion suit works by keeping the inner layers of clothing dry. Between each layer of clothing is a trapped layer of air, which is warmed by the body. These trapped layers of warm, dry air act as insulation layers, which help to protect the pilot from hypothermia. The immersion suit therefore by itself does not offer much in the way of thermal protection – it is only by keeping the inner layers of clothing dry and preserving the trapped layers of air that the suit provides its protection to the fast jet pilot. As a rough guide to the worth of the immersion suit, the average survival time in sea temperatures of 6°C for a pilot wearing standard life support equipment is approximately 30 minutes. The addition of an immersion suit to the clothing of the pilot extends the survival time to more than 12 hours. While the immersion suit is designed to support life in a cold water environment, the preferred solution is that after ejecting into the water the fast jet pilot will enter the personal life raft (part of the ejection seat survival kit) and no longer be subjected to immersion. Even in this scenario, the immersion suit will significantly help to extend survival time. The Liquid Cooling Garment It should be apparent to the reader now that all of the various layers of clothing and life support equipment worn by the fast jet pilot can create a significant thermal burden. The multiple layers of protective clothing worn by the fast jet pilot (especially if combined with an outer immersion suit or CBRN ensemble) can impede metabolic heat loss, making life for the pilot hot and uncomfortable in the cockpit (Balldin et al., 2002; Goswami and Sharma, 2007; Sowood and O’Connor, 1994). This can be quite counterproductive from a human factors perspective: the thermally stressed pilot will suffer from physiological and performance impairment as a result of overheating. Cognitive impairments are seen in terms of vigilance, attention, reasoning, decision-making and judgement, and from a physiological perspective heat stress can reduce tolerance to high +Gz loads (Nunneley and Myhre, 1976; Nunneley et al., 1981). As a result, the liquid cooling garment (LCG) was developed in order to help fast jet crews avoid the heat stress associated with multiple layers of life support equipment. This garment is worn as the innermost layer of clothing, adjacent to the skin of the torso and/or arms. It consists of a lightweight fabric garment embedded with several metres of small diameter tubing, through which cooled water flows. The system requires a pump to drive the fluid through the tubing network, as well as a closed-loop fluid supply and a cooling system (which is often supplied as an integral aircraft system). The fluid temperature is usually not less than 15°C.

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The CBRN Ensemble It is worth mentioning here (for the sake of completeness) CBRN ensembles for fast jet pilots. CBRN is an acronym that stands for Chemical, Biological, Radiological, and Nuclear warfare (replacing the pervious acronym of NBC – Nuclear, Biological and Chemical warfare). Clearly, the use of CBRN ensembles implies that the operating environment of the fast jet has developed into a worstcase scenario, and reflects a critically high level of risk to the crews. The purpose of a CBRN ensemble is intended to offer the crews some protection against the deadly hazards created by exposure to various biological, chemical and nuclear weapons (usually classed as weapons of mass destruction, WMD). The ensemble is designed to eliminate the possibility for an airborne agent such as a chemical or biological weapon to enter the respiratory system, as well as eliminating the potential for skin contact with chemical, and biological agents. The best protection from respiratory exposure is to ensure that the breathing system used by the pilot is fully self-contained. If the aircraft system uses gaseous or liquid oxygen systems, these function independently of external air sources, thus effectively protecting the pilot from chemical and biological agents. An inline mask filter could be used to provide a level of last-resort protection. In aircraft with OBOGS systems fitted, the emergency oxygen system can be used to give the pilot access to a self-contained and completely independent breathing system. Under normal circumstances, the fast jet pilot is almost completely covered by clothing and life support equipment, other than parts of the neck and face. In the CBRN context, a completely enclosed suit is worn to eliminate the potential for skin exposure to toxic agents. A specially constructed suit, usually made of an impermeable material such as rubber (but could also be reinforced nylon), with an inner filter layer impregnated with activated carbon, will provide a degree of resistance to chemical and biological agents, as well as some radiation protection (depending on the intensity of the radiation).Some of these suits are more breathable than others, in that they allow air, sweat and moisture to pass through the suit while a filter layer limits the entry of toxic agents. Such breathable suits tend to be more comfortable to wear than the totally impermeable rubber suits, but have shorter useful lives. CBRN suits cover the entire body, including the head, and are generally cumbersome and not optimised for in-cockpit use. Other alternatives to the full suit include a hood with an integrated oxygen mask, designed to be worn under the helmet, which effectively isolates the neck and face from exposure to the external environment. Despite the comfort and movement restriction issues associated with these suits and hoods, however, in a high-threat CBRN environment they are a necessary element of the overall suite of life support equipment for the fast jet pilot.

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Anthropometry It is now worth briefly considering the role of anthropometry in providing life support equipment to the fast jet pilot. Anthropometry is the scientific field dealing with measurements of the human body and its various components (standing height, sitting height, leg length, functional reach, chest circumference, and so on). While a comprehensive discussion of anthropometry in aviation is beyond the scope of this book, some general comments can help in the present discussion of fast jet life support equipment. Humans come in a myriad of different shapes and sizes. Fast jet pilots are selected by their air forces according to strict medical and health parameters, which tends to make them a population of relatively lean individuals of average height and weight. The fast jet cockpit has only limited adjustments available, usually in terms of sitting height only (and then only a small degree). As such, the fast jet cockpit will not be an ideal environment for individuals at the 5th and 95th percentiles for height. This is an important consideration. A fast jet pilot with a sitting height in excess of the upper limit for a particular cockpit may find him or herself sitting uncomfortably close to the canopy, and at a height too high for a predictably safe ejection. If the head sits higher than the top of the ejection seat, then the potential for injury is increased. If canopy breakers are fitted to the seat head-box, they may be redundant if the pilot’s head hits the canopy first. Once out of the aircraft, the windblast hitting the pilot’s face may force a hyperextension of the neck if the head is too high relative to the head-box of the seat. This can lead to serious injury and even death. Ensuring that the pilot’s physical dimensions fit within the safe ejection envelope of the seat and the safe, comfortable working dimensions of the cockpit is an important anthropometric consideration. Pilots that are too tall and/or have long lower limbs are also problematic for ejection seats. The risk of dynamic overshoot and its potential to cause significant injury are increased in situations when the legs of the pilot are too long for the cockpit, leading to the upper thighs not being in contact with the seat pan during the ejection catapult phase. The weight of the pilot is also an important consideration. Too little or too much weight may put the pilot beyond the safe ejection envelope of the seat. Fast jet life support equipment needs to come in a sufficient number of sizes that all pilots can be adequately fitted with the equipment. For example, wearing a G-suit that is too big will not give the desired level of protection. Similarly, helmet fit (as mentioned earlier) plays a crucial role in optimising impact protection, comfort and its role as a mounting platform for various items of flightcritical equipment. The application of anthropometry is not an exact science, nor is it a static one. Indeed, in an Indian Air Force study (Sharma, 2007), a fast jet trainee pilot population was anthropometrically measured twice, a year apart. Their findings showed that at the time of the second set of measurements, the pilots were on average slightly taller, slightly heavier and with slightly longer legs. Tellingly,

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when the anthropometric data were applied to their aircraft types, only 57 per cent of the pilots were fit for selection (down from 62 per cent a year earlier). According to the authors, sitting height is the most important anthropometric parameter for fast jet pilots, due to the requirement to fit within the safe ejection envelope (Sharma, 2007). Aircrew Equipment Integration So far this chapter has examined fast jet life support equipment on an individual item basis. However, it must be remembered that the fast jet pilot will wear most (if not all) of these items at once. Moreover, much of the life support equipment is worn but not used for its intended purpose. For example, an immersion suit might be worn in order to protect the pilot from the risks of cold water immersion, but if the mission proceeds as planned and no ejection takes place, then the immersion suit was worn but not technically used for its intended purpose. The pilot in that situation has had to contend with the limitations imposed by the immersion suit (heat load, movement restriction) while conducting a normal mission, possibly with a high workload. Aircrew equipment integration is the process by which all of these items of life support equipment are assessed as an integrated whole. The aim is to ensure that any two items of equipment or clothing do not adversely interfere with each other, that no item of life support equipment compromises the task of flying the aircraft, and that the entire ensemble is comfortable for the pilot. Aircrew equipment integration thus serves to maximise the combined effectiveness of the life support equipment worn by the pilot while at the same time minimising or eliminating any adverse impact on the operation of the aircraft. Aircrew equipment integration is effectively an exercise in maximising form, fit and function. To do this, the integration process can be considered to involve assessment of life support equipment according to three main criteria: normal procedures, escape considerations, and in-flight operations. Under the normal procedures criterion, the life support equipment is examined in terms of how easily the pilot can put on and take-off the equipment, noting carefully if it snags other items or in any other way is problematic in terms of adverse interaction. Similarly, the fast jet pilot must be able to walk out to the aircraft, enter the cockpit, strap into the ejection seat and operate all the equipment in the cockpit safely, efficiently and with no adverse interaction (for example, snagging, restriction of movement, reduction of visibility, less than full range of operation of aircraft controls). The life support equipment is also assessed in terms of its durability. Under the escape conditions criterion, the integrated life support equipment assembly is assessed in terms of how easily an emergency ground egress from the aircraft can be carried out, as well as a full range of ejection seat testing (including parachute deployment tests and live ejections of instrumented test mannequins wearing the full assembly of life support equipment). The equipment should not

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restrict the pilot from making an emergency ground egress or ejecting, and should not in any way impede or adversely interact with the escape system. The final criterion involves ensuring that there is no adverse interaction created by the life support equipment when being used in-flight. This involves actual flight testing of the equipment in an appropriate test aircraft, and may also involve the use of simulators and even centrifuges for high +Gz testing of the equipment. Durability, compatibility and lack of adverse interaction are again all assessed in what represents the actual operating environment of the equipment. Furthermore, such testing allows a full range of environmental extremes (temperature, humidity, pressure, and so on) to be factored into the assessment. Once the life support equipment has been cleared through this often exhaustive process, the fast jet pilot can have every confidence that their life support equipment will function as required and protect them from the various hazards that their operations normally expose them to.

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Chapter 6

Situational Awareness Previous chapters have demonstrated the complex and challenging nature of fast jet operations. The significant human factors and performance limitations faced by fast jet aircrew while operating in a high-risk environment need to be managed successfully. The key to this is good situational awareness (SA) of the crew. While SA is a complex phenomenon, it can be achieved through accurate and timely processing of information derived from the fast jet cockpit and its various sensor and display systems. Combined with an optimised human–machine interface, this can help maximise the SA of the crew and increase the chances of mission success. It is beyond the scope of this book to provide a detailed academic treatise on SA. Rather, the intent of this chapter is to examine SA from a fast jet pilot’s perspective, with a major emphasis on the information exchange between the pilot and the environment. This exchange is heavily dependent on the quality of the information supplied by the cockpit sensor and display systems, as well as on how effectively the information is processed by the pilot. The fast jet pilot’s SA, therefore, lies in their ability to process and make use of all the available incoming information from modern sensor and display systems, as well as force multipliers such as airborne early warning and control aircraft. The focus of this chapter, then, is on fast jet aircrew situational awareness. Firstly, the concept of SA will be explored, before examining key elements of cockpit design and layout, the sensor systems in modern fast jets and the display systems in the cockpit. All of these systems are designed to give crucial SA-enabling information to fast jet pilots, so that they can safely exploit the characteristics of the aircraft and complete the mission. In overall terms, good SA will improve the reliability and effectiveness of the fast jet as an integrated weapons system. Defining Situational Awareness It is important to understand what is meant by the term situational awareness. Endsley (1988) defined SA as: The perception of the elements in the environment within a volume of time and space, the comprehension of their meaning, and the projection of their status in the near future.

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A practical sense of what SA means to a fast jet pilot operating in a highly dynamic environment is given by Major John R. Boyd, a USAF fighter pilot who flew in the Korean War: He who can handle the quickest rate of change survives

SA is the one ingredient that separates the successful fast jet pilot from the less successful – good SA gives the fast jet crew a significant operational advantage. This is even more so when there is a relative disparity in SA between the fast jet pilot and their adversary – he who has more SA has more options. Endsley’s model of situational awareness involves three levels, contained in his definition above (Endsley, 1995). Level 1 situational awareness involves perception of the elements in the environment. Level 2 involves comprehension of the current situation, and Level 3 involves projection of future status. To develop an accurate sense of situational awareness based on these three levels requires ongoing cognitive input, accurate and timely information processing and integration of all features of the situation. A modern fast jet is typically wellequipped to provide all relevant information to the pilot via its sensor systems and displays. However, for proper SA the fast jet pilot must gather all the available information and process it appropriately in order to understand what is happening now and what is going to happen in the near future. Clearly anything that can affect cognitive function and information processing will therefore have an adverse effect on SA. The various physiological and psychological challenges inherent in the fast jet environment, alone and particularly in combination, can affect cognitive function (and in particular the processing and integration of safety-critical information) and therefore interfere with the development and maintenance of SA. The information that a fast jet pilot needs in order to develop good SA can be thought of as either external (originating from outside the cockpit) or internal (originating from inside the cockpit). While this distinction is helpful for the purposes of description in this chapter, it is somewhat arbitrary and there is overlap between the two sources of information. Furthermore, a fast jet pilot will gather information from both sources concurrently. External information is largely visually derived. In an air-to-air engagement, the fast jet pilot can see the adversary aircraft and determine its relative energy state and its attitude, and use this information to determine what might happen next (in terms of the geometry of the engagement). This requires the fast jet pilot to have a comprehensive understanding of not only their own aircraft’s performance capabilities and limitations, but also that of their adversary. Visual clues as to where on the energy management spectrum the adversary lies can allow a fast jet pilot to rapidly and accurately develop good SA and turn this to tactical advantage. Where these visual cues are missing or confusing (such as when the engagement involves an unfamiliar adversary aircraft) the opportunity to develop and exploit SA for tactical advantage is reduced.

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Similarly, operations against ground targets also use externally derived SA information. Terrain awareness and recognition, as well as assessment and location of ground-based threats during the ingress and egress phases of the ground attack, are all visually based. Good pre-flight mission planning (and even rehearsal) can help create good real-time SA. Internal information is provided by the aircraft itself. This information can be either tactical in nature, or related to aircraft systems. The systems information will give the pilot details on aircraft performance (for example, airspeed, altitude, and so on) and any system malfunction (for example, engine failure). This information is designed to help the pilot fly, manage and preserve the aircraft. The tactical information supplied by the aircraft is designed to help the pilot understand and exploit the tactical situation they are in. The modern fast jet has a multitude of different display and sensor systems in order to give the crew the information they need to develop and maintain good SA. These displays and sensors will be considered later in more detail. The cockpit of the fast jet is where these systems are housed, and it is worth first understanding the nature of the typical fast jet cockpit. The Fast Jet Cockpit The modern fast jet cockpit is a workplace like no other. It has evolved substantially from the early era of fighter and attack aircraft. The rapid development of digital technology has seen the instrument panel of yesterday’s fighter replaced by an advanced, electronic display-based cockpit of today. The analogue instrument panel essentially had a dial for each parameter, but the advent of the electronic flight display means that all of this information is now presented on two or three multi-function displays. Furthermore, each display has several menus and pages within it that the pilot can select with a variety of push buttons located around the edge of each screen. The end result is that the modern fast jet cockpit is much less cluttered, has increasingly more automated functions and vast amounts of information are available on demand and when required. The cockpit of a fast jet is the nerve centre of the aircraft. It is here that the interface between the human crew and the aircraft exists, and it is from here that the air war is prosecuted against enemy assets. The highly computerised modern fast jet means that the avionics suite of displays and sensors can process a tremendous amount of information at high speed (with data transfer rates over 50 Mb/second). Increases in on-board computer memory and data storage capabilities, coupled with external high-speed data links, have turned the modern fast jet into an airborne information processing centre with unparalleled capabilities as a weapons platform. Quadruplex digital flight control systems using fly by-wire technology give the fast jet superior handling qualities and agility. All of these capabilities are combined in the cockpit. To exploit them, the human–machine interface needs to be as optimised as possible.

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The throttle and control stick have also been made more complex than previous versions, with a multitude of switches and controls mounted on them that allow the pilot to access essential features while in the manoeuvring or engagement phases. This system is known as HOTAS – Hands on Throttle and Stick. For the typical HOTAS system, the throttles will have the following functions: a radio transmit switch, speed brake control, autothrottle control, exterior light control, chaff and flare dispenser switches, radar elevation controls and a target designator controller (TDC). The TDC is effectively a cursor control for the radar, allowing the pilot to slew the cursor on the screen to designate the intended target. On the control stick, there is the traditional trim switch for pitch and aileron trim control, but also autopilot control, nose wheel steering control, radar controls, a weapons firing trigger, and various multi-directional weapons selection switches (to select guns or different air-to-air missiles, or for multi-role aircraft to select between airto-ground and air-to-air modes). Having these essential controls directly within finger reach during high +Gz manoeuvring gives significant operational advantages to the pilot of a fast jet. SA can be maintained by keeping direct visual contact with the adversary aircraft or ground target while operating the aircraft’s systems (radar, weapons selection, and so on). The fast jet cockpit also typically has a Head-Up Display (HUD) which provides essential flight and mission data directly in the line of forward sight of the pilot. Additionally, the increasing use of helmet-mounted displays means that essential information is presented to the eyes of the pilot independently of where they look. Coupled with weapons sighting systems, the head of the pilot is now as much a part of the modern fast jet cockpit as the fixed electronic displays. There are numerous options for presenting information on displays, and for locating and configuring these displays in the cockpit. In general, however, the modern fast jet cockpit will typically conform to a similar architecture. This is shown in the generic cockpit layout diagram (Figure 6.1). The cockpit can be considered as having four main elements – a set of multifunction displays, the HUD, the Up-Front Controller, and the back-up and aircraft system indicators. The multi-function liquid crystal (LCD) displays (usually three, sometimes two or even four) are known by several different terms, depending on the aircraft type and manufacturer. For example, in the F/A-18 family they are called Digital Display Indicators (DDI). For the purposes of this book, the generic term multi-function display (MFD) will be used. The MFDs are generally 10-centimetre square displays, with various mode-dependent soft-keys around the periphery. The lower display is often used as the horizontal situation display, with a moving map. One of the upper MFDs usually acts as the radar display. The next element is the HUD, sitting above the instrument glareshield. Immediately below is the Up-Front Controller (UFC). The UFC is used to select various modes for the autopilot and navigation systems, radios and sensor systems, as well as weapon delivery data. In the latest-generation fast jets such as the F/A18 E/F Super Hornet, the UFC uses a touchscreen display. The last element is the

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Head-Up Display Canopy Bow Up-Front Controller Right Multi-Function Display

Left Multi-Function Display

Engine/Fuel System Indicators

Figure 6.1

Horizontal Situation Display / Moving Map

Back-Up Displays/ Auxiliary Instruments

Typical fast jet cockpit layout

back-up and engine/fuel instrumentation package, which is usually located either side of the lower HSD. The side consoles of the cockpit contain the throttle quadrant (left side) and various system functions (radios, transponder, oxygen system, G-suit connector, various aircraft system controls, and so on). The fast jet cockpit is still evolving, and greater use is being made of MFD technology. The LCD display screens are not only getting larger (usually 20 × 20 cm), but more capable, with better resolution and with larger colour palettes. More and more aircraft performance and tactical situation data is being presented on these displays. Latest-generation aircraft such as the F-22 and the Eurofighter Typhoon use MFD technology almost exclusively, giving a very uncluttered yet highly data-driven cockpit. Indeed, the F-22 has a total of six LCD panels with no analogue instruments at all. There are four standard MFDs and two smaller up-front panels either side of the Integrated Control Panel (ICP), which is the name given to the UFC in the F-22. The F-35 cockpit represents a significant departure from the standard configuration. It does not have a fixed HUD, and instead uses an advanced helmet-mounted display system and a ‘panoramic cockpit display’ consisting of a single large (50 × 20 cm) full panel width touch screen measuring 50 × 20 cm. Work is currently underway on next-generation fast jet cockpits. Boeing has released information recently on its next-generation cockpit for the F/A-18 E/F Super Hornet, which exploits the latest in consumer electronic device technology (Royal Aeronautical Society, 2013). A large (28 × 48 cm) colour MFD uses touch

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screen technology, and gives the operator the ability to swipe, pinch and expand the displayed image, in much the same way as consumer-based tablet devices. Significantly, the screen can be used for ‘drag and drop’ finger pointing to control and command unmanned combat air vehicles from the back seat of the F/A-18. Such technology and its application in the fast jet environment gives an interesting glimpse into the future. Sensor Systems Sensor systems are vital to the safety and survival of the aircraft, as well as to the successful prosecution of the air mission. The sensor suite on a fast jet collects all the raw data, while the aircraft displays (discussed later) represent the visual interface between the sensor systems and the pilot. Sensor systems are designed to increase the SA of the crew. This section will briefly examine some of the major sensor systems in the modern fast jet. They are of two functional types: aircraft performance sensors, and tactical situation sensors. Aircraft Performance Sensors From an aircraft performance perspective, the sensors are built in to the aircraft sub-systems, and contain various attention-getting devices such as voice outputs from the aircraft, warning tones, horns and so on. These might be supplemented by warnings appearing on the HUD and/or helmet-mounted display (HMD) systems. These warnings are designed to protect the aircraft by alerting the pilot to a potential aircraft-threatening problem (such as an engine fire, for example) and for the appropriate corrective action to be taken. This might ultimately mean sacrificing the aircraft in a critical emergency by having the crew eject. One such aircraft protective system is the Terrain Awareness Warning System (TAWS), as fitted in the F/A-18. This is basically a ground proximity warning system (GPWS) to prevent controlled flight into terrain. It incorporates voice warnings and simultaneous HUD-based visual indications of recovery actions for the pilot to take, based on recovery trajectories calculated by the on-board computer systems. The system also protects against gear-up landings. Tactical Situation Sensors The tactical situation sensors are concerned with the operational mission environment. They are primarily concerned with detecting threats to the aircraft (such as incoming missiles, radar emissions from ground-based missile stations, and so on) and targets to engage (such as adversary aircraft or ground-based enemy assets). Not surprisingly, perhaps, the number of tactical situation sensors and their degree of sophistication has been increasing rapidly in recent years, aided by the increased capability of digital technology. While a comprehensive treatment

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of all possible tactical situation sensors is beyond the scope of this book, it is worth considering a few of the major systems in order to gain an appreciation of the human factors and performance challenges faced by the fast jet pilot. Indeed, what will become evident is not only the complexity of the systems but the sheer amount of information they can provide the fast jet crew, who then need to process and use this information accurately and quickly in a high-threat environment. The sensor systems to be discussed can be categorised into two groups: target detection sensors (such as radar, infra-red search and track, forward-looking infra-red) and threat detection sensors (radar warning, laser warning and missile approach warning systems). Radar Radar (which stands for radio detection and ranging) has been around for over 70 years, but modern systems differ significantly from early generation systems in terms of complexity and capability. Radar is an active detection system, in that it emits electromagnetic radiation of a certain frequency. The F-22 uses the AN/ APG-77 radar system, which is an active electronically scanned array (AESA). The F-35 is to be fitted with the APG-81 system, while the Eurofighter Typhoon has the CAPTOR radar, which is a multi-mode pulse Doppler system. Modern fast jet target acquisition and detection radars have incredible capabilities. They can detect targets at distances beyond 150 kilometres, and adjust their beam angle as distance to target decreases, in order to increase accuracy and reduce the emission load. The systems can also track, prioritise and engage multiple targets simultaneously, in any weather, and also automatically select the appropriate weapon to employ. Some advanced systems can also designate targets for other aircraft, and also track one target while continuing to scan for others (so-called Track While Scan capability). The radar output can also be slaved to helmet-mounted displays for target cueing and sighting purposes. For the attack mission, modern radar systems have a range of missionenhancing capabilities, including a sea and surface search mode, a high-resolution ground mapping mode, a Ground Moving Target Identification (GMTI) mode, and a ‘look down, shoot down’ capability which allows the system to detect low-level targets attempting to hide in the background ground-based radar ‘clutter’. Some systems also have an auto attack mode that slaves the autopilot system to fly the aircraft to the designated target, in order to reduce pilot workload. Two other latest-generation radar capabilities are Low Probability of Intercept (LPI) and Non-Cooperative Target Recognition (NTCR). LPI is an effort to deceive a target aircraft’s radar warning receivers and other electronic countermeasures (ECM), by using various techniques such as power regulation and frequencyhopping. Some latest-generation agile radars can change frequencies over 1,000 times per second. NTCR allows detected targets to be identified as friendly rather than enemy, in order to avoid friendly fire incidents. NTCR technology is a significant improvement on the closer-range radio-based Identification Friend or Foe (IFF) system. Few details exist on exactly how this technology works, but it

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almost certainly exploits the long-range high-resolution imaging and advanced signal processing capabilities of the modern radar system. Infra-red search and track Infra-red search and track systems (IRST) are passive target detection methods. Unlike radar, they do not emit radiation but attempt to detect the presence of infrared radiation sources in the vicinity of the aircraft. These infra-red sources can be the heat signature of aircraft engines and even airframe skin (developed by air friction as the aircraft passes through the air at speed). Since these are passive systems, they have the added advantage of being harder to detect than radar, thus helping to maintain the element of surprise. However, their range tends to be limited in comparison with radar (less than 100 nautical miles), owing to the attenuation effects of the atmosphere and even bad weather. IRST systems are employed in a variety of latest-generation fast jets, including the F/A-18 E/F, the F-35, the SAAB JAS 39 Gripen, theSu-27, the MiG-29, the Eurofighter Typhoon, the Dassault Rafale, and the Chinese Chengdu J-10. The F-35 has an extremely capable Distributed Aperture System (DAS), which combines an IRST system, a missile detection/warning system, and day/night vision capabilities. The F-35’s IRST system searches all around the aircraft’s airspace, in all directions simultaneously to a full 360 degrees. It can automatically detect and track multiple targets simultaneously, and similar to the radar system be slaved to the cockpit displays, the HUD, and the helmet-mounted display and sighting systems for weapons cueing and engagement. Targeting FLIR Forward-looking infra-red (FLIR) systems are essentially cameras that look ahead of the aircraft and convert thermal energy (in the far infra-red (IR) part of the electromagnetic spectrum) into a visible image. The resolution of the image depends on several factors, including the optical properties of the FLIR sensor and the relative temperature differences in the field of view (especially between the object of regard and the background), and is typically a monochromatic grey image. The raw image is usually enhanced via signal processing techniques to provide a higher resolution image. FLIR systems in fast jets tend to be used for either navigation or targeting. It is important to note that image resolution is often at the expense of field of view. Navigation FLIR tends to have a relatively wide field of view with a poorer image quality than targeting FLIR, which has a narrower field of view but generates a higher quality image. As an example, the F-15E uses the Low-Altitude Navigation and Targeting Infra-Red Night (LANTIRN) system, which is an externally mounted dual-pod system. It consists of a wide field of view navigation FLIR pod (which also has a terrain-following radar), a narrow field of view targeting FLIR pod, and a laser weapons designator, with appropriate symbology sent to the HUD.

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Threat detection Threat detection systems are the other side of the equation. It is clearly important to know if the adversary aircraft has detected the fast jet’s presence with its own target acquisition systems, and even more important to know if a missile has been launched from the adversary aircraft. This is where threat detection systems play a vital role in self-protection. They are generally part of the overall electronic countermeasures package (ECM) carried by the fast jet. The various systems are somewhat self-explanatory. The Radar Warning Receiver (RWR) can detect and alert the pilot to the presence of an active air-toair radar. The addition of a radar signature database to the system allows the radar signal to be classified according to aircraft type, enabling more accurate threat detection. Similarly, the Laser Warning Receiver (LWR) identifies the presence of a laser, which might be for weapons guidance purposes (ground-based or airborne). The Missile Approach Warning System (MAWS) alerts the fast jet pilot to the threat of an incoming missile. The use of three-dimensional auditory localisation for threat indication in a fast jet has received considerable research interest. Rather than the pilot simply hearing a missile warning system tone in the cockpit, the pilot will hear the tone from the direction in which the missile is approaching. Such SA-enabling technology has the potential to reduce visual workload and create operational advantages in highthreat environments. Displays It is now worth discussing in some detail some of the display systems, particularly in terms of their associated human factors and performance limitations. Space permits only a limited discussion, so the emphasis will be on the HUD and helmetmounted display and sighting systems. Head-Up Displays The Head-Up Display (HUD) has become increasingly sophisticated, especially in relation to its early precursor the reflecting gunsight. It is now an integral part of the fast jet cockpit, and an essential tool for the development and maintenance of SA in the fast jet pilot. The HUD is now considered to be the primary flight display (PFD) for the fast jet pilot. The HUD displays heading, altitude and airspeed information. It also contains a pitch ladder, as in a traditional attitude indicator, a horizon line, a bank angle scale, as well as navigation and communication data (such as distance to waypoint, course deviation indicator, radio frequencies selected, and so on). A flight path marker known as the velocity vector is also displayed. The velocity vector is an important component of the HUD data. This indicates to the pilot where the actual trajectory of the aircraft is, which for an agile fast jet might be

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in a different direction to the nose attitude of the aircraft. The nose of the aircraft may be 20 degrees high, but if this is at a low airspeed the velocity vector might indicate that the aircraft is descending. The velocity vector thus gives the pilot very powerful information as to the state of the aircraft in trajectory terms, which is clearly vital to good SA, especially in the stress of an air-to-air engagement. In addition to the primary flight data, the HUD also presents information on the tactical situation. The target aircraft is shown on the HUD display, usually with information relating to altitude, airspeed and possibly trajectory information (all of which is derived from either the radar or the selected air-to-air weapon’s tracking system, or indeed both in combination). The HUD will also present an aiming reticle, and display information on range to the target (including closure rate), weapons arming state (armed or not), weapons selected, and manoeuvring information (current +Gz level and peak +Gz level reached). In many fast jets, the HUD also gives weapons firing information. Once the designated target is within range of the selected weapon, the on-board computer systems will determine the optimal firing solution and display a ‘SHOOT’ message repetitively on the HUD. If the weapon is fired at this point, the chances of success are extremely high. The HUD may also then display time remaining to weapon impact. The fast jet HUD clearly gives the pilot tremendous improvements in information processing capability and SA. During the most stressful and high-risk parts of the mission, the fast jet pilots can remain head-out of the cockpit, with

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Angle of Attack Indicator

α = 2.1

7.5

G Indicator

15

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5

5

04,5

Pitch Ladder

Velocity Vector

Airspeed Scale

^

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Heading Indicator

Figure 6.2

Waypoint Caret

3,350

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Mach Number

Peak G

03,5

435

Weapon Arm Status

Weapon Load

Target Indicator

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ARM 6 AIM-9M 0.85 9.0

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Typical fast jet Head-Up Display

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Altitude Scale

Range to Target

Distance to Waypoint 11.5 3.4D 2155

Radar Altimeter

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direct visual contact with the target, and have all essential information directly in front of their eyes. While the tactical advantages are obvious, from a human factors perspective there are some challenges. There is the potential for too much information to be displayed, with visual clutter on the HUD a known issue. Pilots do have the ability to deliberately select out some items of information and declutter the display. Another obvious potential problem is that the HUD is only useful to the pilot when they are looking forward. If pilots are looking sideways or even behind them, the fixed HUD is outside their visual range. This is a practical limitation, and with appropriate training and increased familiarity these limitations can be managed. However, one way to manage the limitations of the forward-fixed position of the HUD is to use a helmet-mounted system, which will be discussed in the next section. Helmet-Mounted Display and Sighting Systems In principle, helmet-mounted displays are designed to give the fast jet pilot primary flight and tactical situation information independent of head position. This eliminates the problems associated with a fixed HUD position, and should therefore improve the situational awareness and tactical performance of the fast jet crew. Helmet-mounted display and sighting systems are now highly sophisticated, and usually integrated with the weapons system of the aircraft. The aim of the system is to provide essential flight information, aircraft performance and tactical situation data to the pilot at all times, but also to facilitate the designation of targets to weapons. These systems combine high-resolution displays positioned in front of the eyes, with a head tracking system and an integrated sensor package. Other forms of helmet-mounted display and sighting systems superimpose sensorderived information on direct outside-world vision. The pilot has a normal unaided view of the outside world, with overlapped sensor information (for example, flight, navigation, aircraft systems, weapon systems, targeting data) projected on the visor. Indeed, so sophisticated have these systems become that they are beginning to make the traditional HUD obsolete (as in the case of the F-35). Helmet-mounted display and sighting systems offer tremendous potential advantages, in terms of increasing SA, reducing pilot workload, improving weapons employment and tactical outcomes. Easier weapons targeting and designation provide faster response times and greater accuracy. Less manoeuvring is required, but if it is still necessary (depending on the circumstances of the engagement) then the essential primary flight data is still in the pilot’s direct vision, helping to maintain good SA despite the manoeuvring. Increasing the amount of time that the pilot spends ‘heads up, eyes outside’ during operations in high-threat environments is particularly helpful in generating and maintaining good SA. Helmet-mounted display and sighting systems also can play a role in reducing the potential for spatial disorientation. The sudden loss of visual cues when in close proximity to

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the ground or in bad weather can be countered by the ready supply of attitude, airspeed and altitude information on the pilot’s visor. Joint Helmet-Mounted Cueing System (JHMCS) Boeing’s Joint Helmet-Mounted Cueing System (JHMCS) is an example of a sophisticated HMD system. It is currently in use in several air forces, and in several models of fast jet. These include the F-22, F/A-18, F-15E and F-16. It uses a magnetic head tracker system for head position referencing, and a display projecting collimated symbology and imagery onto the helmet visor. A Helmet Vehicle Interface (HVI) interacts with the on-board aircraft computer system to generate the signals for the visor display. Using JHMCS, the fast jet pilot can designate targets to air-to-air and air-to-ground weapons by simply looking at the target and activating a switch on the control stick. Cueing from on-board sensor systems such as FLIR and radar help to enhance weapons employment accuracy. The pilot can also view any aircraft performance data or tactical situation data on the display without having to look inside the aircraft. This can help increase SA and reduce cockpit workload by providing aircraft performance information continually in the pilot’s field of view. The combination of JHMCS with air-to-air missiles employing High OffBoresight Seeker (HOBS) technology means that target aircraft can be engaged in a much larger envelope than with conventional systems. Almost any target that the pilot can see can be engaged successfully, while reducing the need to manoeuvre aggressively in a high-threat environment. It is claimed that JHMCS can provide target designation effectively up to 80° either side of the aircraft nose. The Royal Australian Air Force (RAAF) successfully hit a target in March, 2009, using an Advanced Short-Range Air-to-Air Missile (ASRAAM) fired from a RAAF F/A18 using JHMCS with target lock-on being achieved after weapon launch. More significantly, the target was more than 5 km away and behind the wing-line of the F/A-18. A next-generation version of JHMCS will employ a lighter, more balanced helmet, with signal processing being done at helmet level rather than aircraft level. This promises to be an even more advanced HMD system. Night Vision Goggles Flying at night involves operating in an environment in which there is a lack of good quality outside visual cues for aircrew to use as references during flight. Since these cues are important for situational awareness and correct orientation, night operations have a greater risk of visual illusions and spatial disorientation. The requirement to operate at high speed and low level also increases the risks of night flight for fast jet crews. In order to increase the SA of fast jet crews operating at night, devices such as Night Vision Goggles (NVGs) are being used more frequently. While NVGs have

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been used in helicopter operations for many years, the operational advantages that they confer as SA-enablers and force multipliers have resulted in a trend to increased use in fast jet operations. NVGs are passive electro-optical devices that intensify what ambient light is available to produce an image that would otherwise be unavailable to the user. They are maximally sensitive to the ambient night sky irradiation, which is also predominantly in the near-infra-red range of the electromagnetic spectrum. The typical architecture of NVGs is a two-tube binocular design (one image intensifying tube per eye), suspended directly in front of the eyes via a helmet mount assembly. Both images presented to the eyes must have a good overlap and be focused correctly to ensure maximum quality of the NVG image. It is a common misconception that NVGs ‘turn night into day’ – this is not correct. The resultant NVG image is monochromatic, and in various shades of green (from light to dark). It is a two-dimensional image, and as such is effectively a flat panel display which lacks depth perception. An object is not directly viewed by the user – what is seen is an indirect representation of the object via the electrooptical image intensification process. The NVG image has a limited field of view, in the order of 40° compared with the normal human eye field of view of approximately 210°. As such, peripheral vision suffers dramatically with NVG use. Overall visual acuity suffers dramatically with NVG use. The best visual acuity achieved with NVG use is 6/12, compared with the normal 6/6 during the day. The NVG image also lacks contrast, has poor resolution, and requires practice and experience in order to correctly interpret the generated image. Despite the limitations of the image produced, NVGs allow a greater level of situational awareness than would otherwise be the case during night flight operations. Since more of the outside visual world can be seen (especially ground and terrain details), the aircrew can develop a greater awareness of what is happening outside the aircraft. From a fast jet perspective, there are some important considerations for NVG use in this environment. The reduced field of view of around 40° is a significant issue, which makes the concept of field of regard important. The field of regard is the total area that is capable of being seen. To achieve a large field of regard, the field of view of the NVGs must be combined with head movements in a coordinated scan. This helps compensate for the NVGs reduced field of view, and helps to expand the NVG user’s overall visual awareness. If performed correctly, the field of regard achieved with NVGs and a good scan pattern can be as large as 180°. The advantage of this is that it helps to create a dynamic and regularly updated mental model of the surrounding visual environment, which is very important for good SA. From a practical perspective, NVGs trigger a requirement to ensure that all cockpit lighting is made NVG-compatible, since they are designed to intensify light in the near-infra-red range of the electromagnetic spectrum. Normal visible light will adversely affect the quality of the NVG image.

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The current trend is to move away from the use of stand-alone NVGs in the fast jet environment, and integrate the NVG image (or other form of synthetic vision) into a more comprehensive helmet-mounted display and sighting system. Challenges and Limitations Helmet-mounted display and sighting systems (NVGs or systems such as JHMCS) can impose additional stresses on the fast jet pilot. These systems increase the total weight borne by the head and neck, and depending on the system might force the centre of gravity of the head-helmet complex further forward. This can lead to neck injuries, especially when the tactical environment involves significant head movements, or unfavourable head positions during aircraft manoeuvring, especially under high +Gz loads (Newman, 1997b; Newman, 2002). As was seen in Chapter 3, +Gz-induced neck injuries are common in the fast jet community. The widespread use of helmet-mounted displays is likely to result in an increased prevalence of this important problem, especially when coupled with the expanding agility of the fast jet. Ejection with helmet-mounted systems complicates the loads placed on the neck of the pilot, and can potentially increase the likelihood of ejection-associated head and neck injuries. If they dislodge from the helmet mounting during the ejection catapult phase, helmet-mounted systems can potentially cause a variety of injuries, such as to the lower limbs. Where possible, NVGs need to be removed prior to ejection, but in time-critical emergencies this might not be possible. Additionally, an impact while wearing a helmet-mounted display (especially NVGs) can increase the probability and severity of head injuries sustained during the impact. In addition, the potential for helmet-mounted systems to complicate emergency ground egress needs to be recognised and adequately addressed. There can also be some post-flight eye problems with NVG use. Post-flight eye strain and fatigue may reflect can reflect poor pre-flight NVG focusing. A temporary orange-brown after-image can persist following a period of NVG use, due to the eyes processing green-hued images only while using NVGs and developing temporary retinal photoreceptor fatigue. Temporary depth perception problems following NVG flight can also occur, usually due to incorrect interpupillary distance settings (the distance between the tubes). The wrong IPD setting triggers ocular muscle compensation, which after NVG use leads to fatigue of these muscles and resultant temporary depth perception problems. In some situations, HMDs can actually increase the likelihood of spatial disorientation and loss of situational awareness. Stabilisation of the projected imagery during movement of the head and/or aircraft is vital. An unstable image will lead to increased perceptual difficulties and greater pilot workload, with greater potential for error and loss of situational awareness. Close attention needs to be paid to helmet fit and image stability, especially under high +Gz conditions. The perceptual and cognitive demands on fast jet pilots have increased as a result of the widespread introduction of HMDs and advanced cockpit displays

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systems. Information overload can lead to task saturation and channelised attention, overwhelming the fast jet pilot’s orientation system with visual, vestibular and proprioceptive mismatches leading to an increased likelihood of spatial disorientation and loss of situational awareness (Gibb et al, 2011).In a study looking at recovery from unusual attitudes using HMD symbology as a cue, control reversal errors were seen. The initial reaction of the pilots seemed to be confusion about orientation, leading to an initial control reversal error before correct orientation was achieved and recovery from the unusual attitude completed successfully (Liggett, 2002). Design of the symbology was highlighted as an important consideration in this study. In a Swiss study, the recovery times from unusual attitudes using either the HUD or back-up attitude direction indicator (ADI) were no different (Huber, 2006). Sensor Fusion Sensor fusion (also known as multi-sensor integration) is the way of the future for SA-enabling systems such as helmet-mounted display and sighting systems (Newman, 2006). During flight, the fast jet pilot receives a significant amount of critical mission information relating to aircraft systems, the current tactical situation, the outside-world view, aircraft attitude, flight performance and navigation. All of this diverse yet crucial information comes from multiple sensors, all of which tend to have different capabilities. Sensor fusion describes the process whereby all available sensor information is integrated or ‘fused’ into a single display. This technology combines tactical information with flight performance data and mission information to give the pilot an integrated single-display sense of what is happening in and around the aircraft. Multi-sensor integration technology can include just about any sensor-derived information available: enhanced night vision technology (incorporating night vision goggle (NVG) and/or forward-looking infra-red imagery (FLIR) overlays), HUD symbology, aircraft systems information, weapon aiming cues and sighting systems, threat detection systems (including three-dimensional localised auditory stimuli), ground collision avoidance (synthetic vision systems coupled with ground images or a stored digital topographic database) and situational displays. These systems can also incorporate information data-linked from other remote sources, such as other fast jets, airborne early warning and control aircraft, or even ground-based stations. This is particularly important in the modern digital battlespace, where network-centric warfare employs an integrated approach to multi-platform war-fighting. As has been seen in earlier sections, much of this is already underway in latest-generation fast jets employing advanced helmet-mounted displays and sensor suites. A degree of sensor fusion is standard technology in aircraft such as the F-22, F-35 and Eurofighter Typhoon. It allows for reduced pilot cognitive workload, increased automation (including target selection and prioritisation), the

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absence of conflicting data being presented to the pilot and far less need for crosschecking with other displays. All of this is aimed at improving the SA of the fast jet pilot by providing a single reference source of information. The Eurofighter Typhoon’s sensor fusion capability is achieved via its Attack and Identification System (AIS). This system integrates all available data, from either on-board sensors (radar, IRST, weapons systems, ECM package) or external sources such as airborne warning and control system (AWACS) aircraft or other Typhoons via a data link. Another element of sensor fusion technology is direct voice input (DVI), where some of the aircraft systems can be activated and controlled via the voice of the pilot. This can even extend to some weapons functions such as selection and arming. Limited DVI technology exists in some latest-generation aircraft such as the Eurofighter Typhoon and the Dassault Rafale. The F-35 is also designed to incorporate some DVI technology. Sensor fusion is an intuitively appealing technology. It offers considerable tactical advantages, but there are many unresolved issues, including those discussed earlier under challenges and limitations of helmet-mounted systems. In overall terms, sensor fusion technology must be enabling, not disabling from a cognitive workload point of view. Ideally, the tactical, operational and flight safety advantages of such technology will far outweigh any biodynamic, cognitive and pilot health disadvantages the system may create. This will require concentrated human factors research, careful system design, and a thoughtful approach to implementation. The major challenge for the fast jet pilot of today is not physically flying the aircraft, but employing it as a fully integrated airborne weapons system in the modern digital battle space. As a result, well-developed SA has never been more important. Information management and interpretation to aid SA and decisionmaking during operations in high-threat environments are significant human factors challenges. Improving the quality of information derived from aircraft sensors and presented on cockpit or helmet-mounted displays is a major challenge, as is optimising the human–machine interface. While sensor fusion technology potentially shows the way forward, understanding the cognitive, psychological, biodynamic and aeromedical issues involved in the deployment of this technology is of crucial importance.

Chapter 7

Escape In an aircraft emergency, the ability to successfully escape from the aircraft can mean the difference between life and death. Thousands of fast jet aircrew around the world have been saved by the use of their ejection seats. While ejection is a life-saving measure, it does carry with it a risk of injury. However, proper training in the correct ejection technique can significantly reduce the risk of injury, while at the same time giving aircrew added confidence in the ejection system. In this chapter, the history of the ejection seat is briefly reviewed, before a close examination of how a modern ejection seat works. Survival outcomes and the various types of ejection injury are considered, followed by a brief look at some post-ejection and survival issues. Finally, a discussion of the technology being developed for the next generation of ejection seats provides a glimpse into the future for this important life-saving device. History of Escape from Aircraft The development of the ejection seat was a direct consequence of the technological advances in aircraft design and performance that occurred during the Second World War. Prior to this conflict, parachutes were the only option for escape from aircraft. As early as 1939, fighter squadrons on both sides were becoming all too aware of the problems of high speed escape from aircraft with increasingly higher performance. Pilots simply could not overcome the high +Gz loads and windblast, especially if the aircraft had sustained combat damage and was in an out-of-control state. The obvious need to escape quickly from a stricken or uncontrollable aircraft spurred the development of an assisted escape solution. Four countries, largely independent of each other, began working on the problem – Sweden, Germany, Britain and the United States. The work done in these countries led to the first operational ejection seats from which today’s highly sophisticated seats evolved. The Germans were arguably the forerunners in terms of developing an ejection seat for their fighter aircraft. Design and development work by the Junkers aircraft company led to the first installation of an ejection seat in an aircraft in 1941. Heinkel produced a seat in 1944 that eventually became the standard German ejection seat, installed in a variety of fighter aircraft, including the Heinkel 162 and the Heinkel 219 nightfighter. In fact, the first successful ejections in Germany were by the two-man crew of a Heinkel 219 on 11 April 1944. By the end of

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the Second World War, more than 60 emergency escapes had been made from German fighters using ejection seats (Newman, 1993). In Sweden, the indigenous J21 fighter aircraft made its maiden flight in 1943 equipped with a Swedish-designed ejection seat manufactured by SAAB. This seat was powered by a single-cartridge ejection gun. The Swedish Air Force did not have long to wait for their first emergency ejection. On 29 July 1946, the pilot of a J21 fighter encountered an inflight emergency and successfully ejected from his aircraft (Sandstedt, 1989). The death of a test pilot in January 1944 perhaps acted as the catalyst for production of the British ejection seat. While test flying an early Gloster Meteor jet fighter for the Royal Aircraft Establishment, the pilot was faced with an emergency and forced to abandon the aircraft. During his attempt at bailing out (equipped only with a parachute), he was rendered unconscious and was unable to deploy his parachute (Newman, 1993). Later that same year, the Martin-Baker Aircraft Company began work on the design and development of an ejection seat (in collaboration with the RAF Institute of Aviation Medicine). This work led to the first live test on 24 January 1945. One of the company’s fitters, Bernard Lynch, was shot up an almost vertical 16-foot test rig to a height of 4 feet. Further tests resulted in a height of 10 feet being reached. A Defiant fighter aircraft was then used for flight trials of the ejection seat. With Brian Greenstead at the controls, the Defiant successfully ejected a dummy ‘pilot’ on 10 May 1945 (Newman, 1993). The first live experimental ejection from an aircraft in Britain was made by Bernard Lynch on 24 July, 1946. At a height of 8,000 feet and a speed of 320 mph IAS, Lynch ejected from the rear seat of a specially modified Meteor Mk III. In June, 1947, the Martin-Baker Mk I seat was adopted for widespread installation in RAF and Royal Navy aircraft, with the first British emergency ejection subsequently taking place on 30 May 1949. In the United States, the first live ejection from an aircraft was carried out by First Sergeant Lawrence Lambert on 17 August 1946, over Wright Field, Ohio. The United States Navy conducted development work in conjunction with the Martin-Baker company, which culminated on 1 November 1946 in the first successful live US Navy ejection, when Lt Furtek, USN, ejected from a Douglas A-26 over Lake Hurst using a Martin-Baker seat. The first emergency ejections from aircraft of both services occurred exactly three weeks apart in 1949. On 8 August, a Navy pilot ejected from his McDonnell F2H-1 Banshee fighter after the engine flamedout. On 29 August, a USAF pilot successfully ejected from his out-of-control F86 Sabrejet (Newman, 1993). In slightly less than 10 years, a significant breakthrough in the problem of escape from high-performance aircraft was made with the development and introduction into service of the ejection seat. Since its introduction in the 1940s, the ejection seat has saved thousands of aircrew lives.

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The Modern Ejection Seat In principle, the ejection seats in use today are basically the same as those early seats of 70 years ago. However, modern ejection seats have evolved to become more automatic, reliable, technically sophisticated and capable versions of the original seats. Today’s ejection seat has more advanced propulsion systems (such as the addition of a rocket motor), microprocessor control technology, advanced body and limb restraint technology integrated into the seat, and a much wider performance envelope (in line with the increasing performance envelope of the modern fast jet). There are several major manufacturers, including Martin-Baker (UK) and Zvezda (Russia), who are continually innovating in order to improve their assisted escape solutions. With the ongoing development of digital technology and thrustvectoring systems, the future ejection seat may well represent a quantum leap in safety for fast jet aircrew. Anatomy The modern ejection seat is an elegant yet complicated engineering marvel. While a comprehensive analysis of the technical details of the ejection seat is beyond the scope of this book, it is useful to consider the fundamental anatomy of the ejection seat, before considering in the next section the typical ejection sequence.

Head-Box Containing Parachute

Upper Harness

Barostatic Time Release Unit

Firing Handle

Manual Over-Ride Handle Seat Back Cushion Arm/Safe Handle Lower Harness

Leg Restraints

Figure 7.1 Ejection seat

Seat Frame

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In general terms, an ejection seat consists of four main systems: 1. The structural system. This is effectively the skeleton of the ejection seat. It consists of two vertical main beams, and two horizontal cross-beams. To this assembly is attached the seat bucket assembly, consisting of a vertical padded seat-back and a padded lower seat pan, to the front of which is fitted the ejection firing handle (in the shape of a loop). Also fitted to this structural system are various operating functions such as the shoulder harness control handle, and the manual override handle. 2. The firing system. This is, as the name suggests, responsible for the actual ejection of the seat from the aircraft. It is also the assembly that secures the seat to the aircraft under normal conditions. This system consists of the ballistic catapult system (operated by explosive charges) and the under-seat rocket motor (which consists of a series of up to 10 solid propellant tubes, a manifold and 4 exhaust nozzles). The ballistic catapult system consists of a series of compressed telescopic tubes, anchored at the base to the aircraft floor and at the top to the main assembly structure of the seat. There are also various ballistic latches and manifolds, an electronic sequencer, a barostatic release unit, a safe/armed handle and batteries that supply electrical power to this system. 3. The parachute system includes the parachute container (the headbox, with a shaped padded front to help with correct head position), the main parachute canopy and drogue, the seat harness, the shoulder harness inertia reel, the drogue parachute deployment sub-system, the leg restraint system (and arm restraint system if fitted), and the emergency restraint release handle. The parachute container may also have canopy breakers fitted on either side. 4. The life support system. This includes the under-seat survival kit (which includes the life-raft and survival kit), the emergency oxygen system and the automatically triggered radio locator beacon. A fuller understanding of how these various systems and subsystems work is given below when the ejection sequence is considered. Performance Specifications While each model of ejection seat will have different performance specifications (usually matched to the particular aircraft it is designed for and fitted to), the modern ejection seat typically has a number of common performance specifications. It is beyond the scope of this book to consider each model of seat individually, so what follows is a general discussion of typical performance characteristics.

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Most ejection seats in fast jet aircraft have so-called ‘zero:zero’ capability. This means that the aircrew can eject successfully while the aircraft is on the ground (zero altitude) and stationary (zero speed). Earlier ejection seats often needed a minimum aircraft altitude and airspeed in order to ensure separation from the aircraft and deployment of the main parachute. The modern seat is fully automatic, such that after initiation of the ejection by the pilot the seat automatically moves through its sequence, with the result that about three seconds after initiation of ejection the pilot will be in descent mode under a fully deployed parachute canopy. In multi-place fast jets, where each occupant has an ejection seat, a command ejection system is used. When this mode of operation is selected, initiation of ejection by either pilot will lead to the ejection of the rear seat first, followed approximately 0.3 seconds later by the front seat. This command system means that one crew member can initiate ejection of both occupants with minimal delay. Ejection seats are designed to egress the aircrew from the aircraft without exceeding the inherent G limits of the body. In general, the human body will cope with G onset rates up to 300G/sec, and with peak G not exceeding +25Gz. As such, a pilot’s chance of surviving an ejection is greatly reduced should these limits be exceeded, and their chance of injury is similarly increased. In general, modern ejection seats produce a +Gz profile in the range of +14 to +16 Gz at an onset rate in the range of 180 to 210 +Gz/second. The firing system will give the seat an initial speed on egress of approximately 27 m/second, and propel the seat to a height above the aircraft of around 80 to 100 feet. The rocket motor can deliver almost 5,000 pounds of thrust, but over only about 0.2 to 0.3 seconds. The main parachute is typically a military parachute, with a 20-foot diameter. Depending on the seat and harness arrangements, a seawateractivated release system may be fitted to ensure separation of the pilot from the parachute on water entry. Most ejection seats are designed for ejections of up to 600 knots maximum. However, supersonically rated ejection seats are fitted to some of the world’s most potent fighters. The Zvezda K-36D ejection seat fitted to the MiG-29 Fulcrum is capable of survivable ejections at speeds of up to 755 knots (1,400 km/h). These seats have enhanced windblast protection and seat stabilisation systems. The Zvezda design bureau claims to have achieved successful operational ejections at speeds in excess of 700 knots. Typical Ejection Sequence The ejection seat must first be armed prior to flight. Normally, the pilot will strap into the harness and get as comfortable as possible before arming the seat. In older seats, arming required the removal of seat pins that locked various critical components (such as the firing handle, the manual override handle, and so on). Modern seats now typically use a single safe/arm handle, which the pilot must

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physically operate. Once this is done, pulling the firing handle will trigger the ejection sequence. When the ejection seat firing handle is pulled, the integrated ejection gun cartridges are fired in rapid succession. The staggered firing of the cartridges helps to generate a sustained increase in gas pressure during the ballistic gun stroke to control the +Gz load being developed. Initiation of ejection energises the on-board thermal batteries which supply electrical power to the ejection sequencer. Upon activation, the sequencer determines the time and sequence at which drogue release, parachute deployment, and seat/man separation will occur. Depending on the type of seat and aircraft to which it is fitted, the canopy may be jettisoned as part of the initial ejection sequence. Alternatively, a miniature detonating cord attached to the underside of the canopy may be activated, which will fragment the canopy above the pilot’s head. In other cases, canopy breakers fitted to the sides of the head-box will shatter the canopy as the seat is propelled out of the aircraft. As the telescopic catapult extends and the seat begins to move upwards, the expanding gases caused by the exploding cartridges will activate the shoulder harness inertia reel, which pulls the pilot back into the seat and helps ensure optimum posture for the ejection. At the same time, connections between the pilot and the aircraft are disconnected, the emergency oxygen system and radio locator beacon are activated, and the leg restraint system pulls the pilot’s lower legs to the front of the seat pan. If fitted, arm restraints keep the arms by the sides of the pilot (as in the Panavia Tornado aircraft). If the seat is a rocket-type seat, the rocket motor pack is ignited once the seat has reached the end of the ballistic gun stroke. This rocket pack extends the acceleration of the seat over a longer time period and helps minimise the peak +Gz reached during the sequence. Once the seat is clear of the aircraft, the small drogue parachute is then deployed (approximately 200 milliseconds from ejection initiation). The drogue parachute helps to stabilise the position of the pilot and seat in the air. This is important, because as soon as the seat and pilot leave the aircraft structure, they are exposed to tremendous wind blast and drag effects. An ejecting pilot will rapidly decelerate from the speed of the aircraft at the time of ejection (for example, taking 1.5 seconds to decelerate from 600 to 250 knots). If the ejection takes place below 10,000 feet, the main parachute is then deployed, and the seat is disconnected from the pilot’s harness and falls free. The pilot is then in the parachute, and descends to the ground. If above 10,000 feet, a barostatic time release unit delays deployment of the main parachute until the seat reaches 10,000 feet. This barostatic time release unit uses an aneroid capsule which prevents deployment of the main parachute above the pre-set altitude (typically 10,000 feet). The requirement for a barostatic unit is a reflection of human performance limitations: if the main parachute were deployed above 10,000 feet the pilot would be subjected to a prolonged risk of hypoxia, extremely cold

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temperatures and a large jolt (‘opening shock’). A parachute opening at 10,000 feet develops an opening shock equivalent to about +8 Gz, whereas at 25,000 feet the opening shock is +16 Gz. The pilot can deploy the contents of the under-seat survival kit by a manually operated toggle on the kit, which then deploys on a lanyard underneath the pilot. The life-raft automatically inflates on contact with water. Importantly, a manual override handle allows the pilot to override the barostatic time release unit if it should fail for some reason. This then allows the pilot to manually deploy the main parachute and initiate separation from the seat. Ejection Posture Given the extreme forces generated by the ejection sequence, adopting the correct posture is essential. As seen above, some of the seat’s systems will forcibly position the pilot as ejection is underway. Ideally, if time permits, aircrew should adopt an optimum position prior to initiating ejection. The correct ejection posture involves sitting well back in the seat, firmly in contact with the seat-back. The head should be held firmly against the head-box, with the eyes looking forward. Every effort should be made to sit as straight as possible. The forces of ejection are in the head-to-foot axis, so correct alignment of the spine with the ejection force vector helps to minimise spinal injuries. The feet should be on the rudder pedals, with the thighs directly in contact with the seat pan, with no gap between the leg and seat. The elbows should be held close against the sides, to avoid contact with aircraft structures as the seat rises upwards. The harness straps should be as tight as possible, with the shoulder harness locked. The helmet visor should be down. The importance of this posture will be seen later in the discussion of ejection injuries. In essence, the correct posture creates a tightly coupled human-seat complex, with no potential for relative movement between them. Also, the spine will be correctly aligned with the resultant ejection force vector, making it more able to tolerate these forces without injury. Survival Outcomes The likelihood of surviving an ejection is statistically very high. A review of the published literature on ejection outcomes reveals that the overall ejection survival rate is in excess of 90 per cent, particularly where modern ejection seats with enhanced capabilities have been used. In a RAAF study, the survival rate was 92 per cent (Newman, 1995), while for the RAF the latest study shows a survival rate of 95.7 per cent for within-envelope ejections (Lewis, 2006).

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Ejecons

700 600

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Survived

400 300 200 100 0

Ejecon Study

Figure 7.2

Ejection survival outcomes

The most common factors contributing to fatal ejection are: • Ejecting outside the performance envelope of the seat. • Delaying the ejection decision. • Damage to the seat (for example, following mid-air collision). Ejecting outside the performance envelope of the seat is sometimes the only alternative that the aircrew have, given the dire circumstances at the time of the emergency. However, in many cases delaying the decision to eject is closely linked to the subsequent outside-the-envelope ejection. In an RAF study, the outside-theenvelope ejection survival rate was only 23.8 per cent (Lewis, 2006). In general, the decision to eject requires a conscious decision to be made by the pilot. In most cases, the requirement to evacuate the fast jet as soon as possible is obvious (out-of-control aircraft, fire, and so on). However, in some cases the pilot may attempt to save the aircraft and as a result stay in the cockpit. When this attempt to save the aircraft fails, the subsequent ejection (if it occurs) may be too late for survival. Delaying the ejection decision is recognised as a major contributing factor to fatal ejection outcomes (Chubb et al., 1967; Farmer et al., 1966; Nakamura, 2007). According to a Japanese study (Nakamura, 2007), the most frequent reason for a

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fatal ejection outcome (in 37.5 per cent of cases) was delaying the decision to eject. In one study (Chunn and Shannon, 1964), the altitude at which the emergency occurred was compared with the altitude at which ejection was initiated. There were 66 cases in which an aircraft emergency occurred above 2,000 feet (the minimum altitude for controlled ejection in this study). In 48 cases, ejection occurred above 2,000 feet and the survival rate was 90 per cent. In the remaining 18 cases, ejection was delayed until below 2,000 feet, and the survival rate decreased to only 72 per cent. A lack of crew coordination in multi-place fast jet aircraft may also play a role in delaying the ejection decision, leading to a fatal ejection outcome. In some cases, pilots waiting for the second pilot to eject successfully first before ejecting themselves results in insufficient time remaining (Farmer et al., 1966). Language issues in training aircraft (particularly where the pilots are from different countries) may exacerbate this (Farmer et al., 1966). Clearly, a lack of procedural training in how and when to eject is also problematic (Farmer et al., 1966; Nakamura, 2007). Whatever the reason, delaying the decision to eject may not afford the seat sufficient time to complete its life-saving sequence. The aircrew’s decision to eject needs to be made without delay. In many cases, it is made in the pre-flight planning phase, where various scenarios are identified that would lead to an ejection. Interestingly, in his study of pilots who have made multiple ejections, Smelsey (1970) found that survival rates were higher on the second ejection than the first. Furthermore, their first ejection experience had a positive impact on their subsequent ejections, presumably due to familiarity with the ejection process and confidence in the system. As has been discussed in Chapter 1, the modern fast jet frequently operates at high speed and at low-level. This creates a risk of damage due to ground-based small arms fire or surface to air missiles, or inadvertent impact with the ground and obstacles such as trees and man-made structures. Any of these events may severely incapacitate the aircraft, such that a low-level ejection may need to occur to guarantee the safe survival of the crew. However, an ejection at low altitude puts the crewmember closer to the margins of the safe ejection envelope. Does an ejection at this low altitude increase the risks to the crew, by reducing the overall success rate of the ejection? A low-level ejection is by nature a time-critical emergency, where the altitude and speed combination give the aircrew an extremely small window of opportunity for successful ejection. In contrast, a higher altitude ejection gives more time for the seat to work its way through the ejection sequence, ensuring full parachute deployment and arguably a more stable arrival on the ground. The results of a recent study suggest that low-level ejections do have an overall higher fatality rate than ejections occurring at altitudes greater than 500 feet (Newman, 2013). In this study, higher level ejections (above 500 feet) have a survival rate consistent with the published overall ejection survival rate, which is greater than 90 per cent (Newman, 1995; Sandstedt, 1989; Visuri and Aho, 1992), while low-level ejections have a statistically lower survival rate. The results show

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that a low-level ejection is 5.65 times more likely to result in a fatal outcome than one above 500 ft (Newman, 2013). There are many factors that contribute to this higher low-level ejection fatality outcome. These include the nature of the emergency necessitating ejection (for example, low-level loss of flight control, fire or structural failure of the aircraft), the aircraft’s operating parameters at the time of the ejection (for example, high speed, adverse bank angle, high rate of vertical descent), and the close proximity to terrain and ground obstacles (trees, pylons, ridges, and so on) once separation from the aircraft has been achieved. All of these factors may leave insufficient time for the ejection sequence to be completed and full parachute deployment to be achieved. Ejection Injuries Despite the life-saving capabilities of the modern ejection seat, ejection injuries are not uncommon (Collins et al., 1968; Fleming, 1979; Newman, 1995; Lewis, 2006; Milanov, 1996; Moreno Vázquez et al., 1999; Read and Pillay, 2000; Rice and Ninow, 1973; Rowe and Brooks, 1984; Shannon, 1970; Smiley, 1964; Smiley, 1968; Visuri and Aho, 1992; Werner, 1999; Williams, 1993). These range from major injuries, such as vertebral compression fractures (Chubb et al., 1965; Ewing, 1971; James, 1991; Jones, 2000; Lewis, 2006; Newman, 1995; Osborne and Cook, 1997; Rotondo, 1975) and head and limb injuries (Combs, 1980; Warburton, 1993), to minor injuries, such as bruises and abrasions (Newman, 1995). The mechanisms underlying ejection injuries are a function of several factors. These include the ejection forces, the stature and boarding mass of the aircrew, the nature of any head-mounted equipment (for example, night vision goggles or helmet-mounted sighting and display system), and the adoption of the correct ejection posture by the aircrew. In reviewing the possible injuries that may arise during ejection, it is useful to consider them in terms of the various phases of the ejection sequence. The sequence (previously described in detail) can be thought of as consisting of five phases: 1. 2. 3. 4. 5.

The catapult phase The aircraft separation phase The in-seat flight phase The parachute descent phase The landing phase.

The Catapult Phase The catapult phase is the most dynamic and explosive phase, characterised by the exposure of the seat occupant to the significant forces involved in getting the seat to begin its upward trajectory. It is a violent phase, and many if not most of the ejection-related injuries sustained by aircrew are associated with this phase.

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One of the major injury types associated with ejection is vertebral fracture. The large initial force of ejection (+15 Gz peak, 200 G/sec onset rate) is transmitted through the long axis of the body, and is therefore particularly borne by the spine. This force may exceed the load-bearing ability of the vertebral bodies and lead to a breach of their structural integrity. The resultant compression fracture, while painful, is generally stable and does not cause damage to the spinal cord. Neurological damage resulting from such fractures is thus quite rare. The most atrisk part of the spinal cord is the thoracolumbar region (especially around the T12 vertebral body, as this has the highest loading per unit area), as seen in Figure 7.3. In a RAF study of 232 ejections, the rate of spinal fracture was 29.4 per cent (Lewis, 2006).A similar study in the Royal Australian Air Force covering a wide range of ejection seats over a large time period showed a spinal fracture rate of 35 per cent (Newman, 1995). In general, the aviation medicine literature suggests that the spinal fracture rate for ejection is in the region of 18 to 35 per cent (Kaplan, 1974; Lewis, 2006; McCarthy, 1988; Newman, 1995; Smelsey, 1970; Visuri and Aho, 1992). In practical terms, aircrew ejecting from a stricken aircraft have at least a 1 in 5 chance of sustaining a vertebral fracture. It is also worth noting that ejection can sometimes cause more than one vertebral fracture. In some reported cases, up to five vertebral fractures have been sustained by a single ejectee (Newman, 1995). Interestingly, in those aircrew who have ejected on more than one occasion and sustained vertebral fractures, the

Vertebral Ejecon Fracture Distribuon in RAAF Macchi Aircra 10 9

Number of Vertebral Fractures

8 7 6 5 4 3 2 1 0 T1

T2

T3

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T5

T6

T7

T8

T9

T10

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Vertebral Body

Figure 7.3

Ejection vertebral fracture distribution in RAAF Macchi aircraft

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L5

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vertebral body that fractures on the first ejection does not fracture on the second. The healing process tends to make the vertebral body stronger than before, thus making the adjacent vertebrae more susceptible to fracture on the second ejection (Smelsey, 1970). Of course, if a good ejection posture has been adopted then the likelihood of ejection-induced vertebral fracture can be reduced. The explosive forces of ejection can force the head forward and down, sometimes making contact in extreme case with the chest. Given the standard seat-back angle of an ejection seat of 13°, a +15 Gz ejection can create a forward flexion component of approximately +3.5 Gz. The shoulder harness restraint system will limit forward movement of the torso, but the unrestrained head of the seat occupant may succumb to this flexion force. Poor ejection posture can lead to a problem known as dynamic overshoot, which can increase the potential for injury. This phenomenon largely relates to the position of the legs in relation to the seat pan. If the legs are not extended fully, an air gap will exist between the bottom of the thighs and the top of the seat pan. As the seat fires and begins to move, this air gap will close. The seat pan will then make contact with the thighs at a potentially higher +Gz load than would have occurred had the legs been tightly coupled with the seat. The potential for fracture of the femurs due to the seat pan hitting the legs at around 25 m/sec is significant. As the seat travels upwards, contact with aircraft structures such as canopy surrounds and cockpit sills can occur, leading to traumatic injuries. This is much more likely when the aircraft is not stable, as an out-of-control aircraft will make the ejection environment more complicated. The Aircraft Separation Phase The aircraft separation phase involves several challenges. Firstly, the aircrew member must clear the canopy. The canopy, as discussed earlier, can either be jettisoned as part of the ejection sequence, or the aircrew-seat complex can pass directly through the canopy. In the latter case, the ejection seat canopy breakers will strike the canopy first and fracture it, allowing the ejecting crew member to pass through the hole created. Similarly, if a miniature detonating cord (MDC) is fitted to the underside of the canopy, this will fire as part of the sequence and shatter the canopy in time for passage of the seat and occupant through the hole created. The MDC is a lead-covered shaped exploding cord, the remnants of which (so-called ‘MDC spatter’) can lead to burns to unprotected areas of the pilot, such as the face and neck (James, 1991). Using canopy breakers to penetrate the canopy can create a higher risk of neck injuries, depending on ejection posture and sitting height of the aircrew (Yacavone et al., 1992). Having separated from the aircraft, the ejectee is then confronted with windblast, which is a direct function of the prevailing airspeed. This windblast can lead to limb flail if they are unrestrained, which can lead to traumatic injuries. As an example, a test pilot ejected from a stricken F-100A fighter on 26 February 1955 at supersonic speed (Mach 1.05), far outside the performance envelope of his ejection

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seat. He sustained major injuries, including internal haemorrhaging, a perforated intestine, liver damage and eye and ear trauma, all of which were attributed to windblast. He eventually recovered and returned to flying fast jets. The linear decelerations imparted to his body by exposure to the supersonic airstream were massive – at head level, a peak deceleration of +64 Gz at a rate of onset of 700 G/ sec; at torso level, a peak G of +50 Gz at a rate of onset of 1300 G/sec (Newman, 1994). The In-Seat Flight Phase Once successfully clear of the aircraft, the next phase involves falling to Earth in the seat, stabilised by the drogue parachute system. This phase will only be of significant duration at high altitudes (that is, above the pre-set barostatic time release unit altitude). The main opportunity for injury during this phase is due to the tumbling that may occur before the drogue parachute has achieved stability for the seat. During the in-seat flight phase, the occupant is at risk of hypoxia (offset by the emergency oxygen system) and cold (hopefully offset to an extent by appropriate clothing). However, if the pilot activates the manual override handle owing to a false perception that the main parachute has failed to deploy and that the altitude is much lower than it actually is, there is a risk of hypoxia and cold injury, since the occupant will separate from the seat and be under the main canopy for a much longer period of time. The Parachute Descent Phase The major issue with the parachute descent phase is in the initial stage, when the main parachute is deployed. The jolt associated with main parachute deployment (known as ‘opening shock’) can lead to injury, as can making contact with parachute risers during the deployment phase. Once under a fully deployed main parachute, the ejectee has limited options to steer the parachute, while preparing for the landing. Manual deployment of the survival kit should occur during this phase. The Landing Phase Finally, the landing phase needs to be managed. There is potential for injury in this phase, which is amplified by the presence of rough or uneven terrain, or heavily treed areas. Landing on rough, uneven terrain can lead to lower limb injuries, particularly in the knees and ankles. Performing a proper parachute landing fall will minimise this potential, but the nature of terrain can make preventing injury more problematic. Clearly, entering trees while under a parachute opens up many opportunities to sustain injuries. If the landing is in to water, the priority must be extracting oneself from the parachute harness and successfully entering the deployed, inflated liferaft. While possible to breathe through the parachute if it covers the head of

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the immersed pilot, this is a claustrophobic and unpleasant experience. A large parachute can fill with water and act as a sea anchor, or remain inflated and drag the pilot through the water. Disengaging from the parachute harness and entering the life-raft will significantly reduce the potential for drowning. Post-Ejection Considerations Once the pilot is on the ground and out of the parachute harness, the ejection can be considered to be complete. However, there are several post-ejection considerations that warrant some brief attention here. It is important for the fast jet ejectee to consider their potential injury state. In general, it is best to assume that there is a vertebral fracture present, and to therefore limit movement to what is absolutely essential. This would include getting into the life-raft, moving to a clear, safe area of terrain, and so on. The ejectee should then take whatever first aid actions are required, using the kit contained in the survival pack. After these immediate actions have been taken, standard survival considerations apply. The first priority is protection. Getting into the life-raft, removing themselves from any dangerous terrain (for example, cliff edge) will help with this. Also, getting out of the elements (such as rain, snow, wind, direct sunlight, and so on) will help protect the ejectee from potential further injury or reduced survival time. Location is the next priority, and usually this is already taken care of during the ejection sequence. Activation of the seat-based radio locator beacon and the transmission of a mayday call will help alert ground stations to the general position of the ejectee. Other aircraft in the area can also act as airborne relay stations, and can transmit an accurate position fix, as well as coordinate subsequent rescue efforts. For location purposes, the survival kit (or the pilot’s personal kit) contains a radio transceiver for establishing contact with rescuers. Also, signalling devices such as a heliograph (a signalling mirror) can be used to attract attention from aircraft, by reflecting sunlight at an approaching aircraft. Strobe lights or signal beacons can also be useful in this setting, but battery life will be an important factor. Similarly, flares can be used to attract attention. The tactical environment, however, might mean that these obvious measures cannot be used owing to proximity of enemy ground forces. In non-combat conditions, the recovery of the ejected pilot is usually relatively rapid. Ejections behind enemy lines or in a hostile combat zone make the recovery efforts more problematic, and the efforts of the possibly injured ejectee to evade capture make locating them more difficult. Water and food are the next priorities, but these are generally only factors when recovery will be delayed, as in a combatrelated ejection. How best to deal with these issues is well covered in standard combat survival training for fast jet aircrew.

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Given the potential for vertebral fracture, the rescue will generally be made with the ejectee in a stretcher being winched into the rescue helicopter. It is important that ejectees allow this to happen. The surge of adrenaline through their bodies after surviving an emergency situation and ejection will likely mask any pain from a simple compression fracture. Ejecting aircrew need to allow the rescuers to do what is necessary, as they have well-established rescue protocols for the safe retrieval of ejected aircrew. Medical care of the ejectee tends to focus on pain relief and identifying the injuries sustained. Plain X-rays, CT scans and bone scans are usually used to identify the presence of vertebral fractures. In general, these heal without much external assistance. Pain relief, early gentle ambulation and physiotherapy help significantly. Any complicated injuries become the subject of standard medical care, outside the scope of this book. History shows that fast jet aircrew can expect to return to full flying status once recovered from their injuries. As mentioned previously, a history of vertebral fracture on ejection is not necessarily repeated on subsequent ejections, and the initial fractures (once healed) are no more susceptible to ejection fracture than other vertebral bodies. One issue to bear in mind is the psychological consequences of surviving a lifethreatening emergency and ejection. The significance of this to the affected aircrew should never be under-estimated. Some aircrew are more resilient than others, and in many cases the nature of the emergency plays a role in determining whether there are any significant post-ejection psychological issues. For instance, a mid-air collision in which some aircrew ejected and survived and others did not (especially if this is the situation in the one aircraft) has more potential psychological issues for the surviving ejectee than a planned, controlled ejection from a malfunctioning yet stable aircraft. In a study of Indian Air Force ejectees (Taneja et al., 2005), it was found that many of them suffered from temporal distortion during the ejection and a significant degree of emotional arousal (due to the life-threatening nature of the event) which can affect their overall psychological recovery from the ejection. Next-Generation Seats Has the ejection seat reached the end of its development potential? The answer to this question is definitely no. As fast jet aircraft continue to improve their performance and capability, so too must the ejection seat evolve in order to continue to offer the aircrew an escape solution. There is much that can be done to improve ejection seat performance. The increasing integration of digital microprocessor technology into the ejection seat offers tremendous potential performance improvements. An on-board flight computer which receives information about aircraft attitude, altitude and airspeed on a regular basis could assess the threat level to the seat at the moment of separation from the aircraft, and directly control the remainder of the ejection

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sequence in order to determine the optimum escape solution. A key element of this would be the integration of a thrust-vectoring control (TVC) system into the rocket motor system. The TVC system (using a combination of thrust-vectoring efflux nozzles and supplementary attitude stabilising motors) would combine with the on-seat flight data computer to calculate and deliver the best ejection seat trajectory solution for the prevailing circumstances. The force generated by the propulsion system could even be titrated to give the lowest force necessary to clear the aircraft and nearby obstructions, thus ensuring satisfactory escape and minimising the potential for injury. The advantage of such a system is well illustrated by the low-level ejection situation (especially in a non-level attitude). The seat could steer itself away from the terrain (even if the ejection occurred during inverted flight) and allow parachute deployment and seat-man separation to occur at the most optimum altitude. This could be augmented by an auto-ejection capability, where the decision to eject is effectively made by the seat’s computer, based on the optimum ejection solution and the prevailing aircraft parameters. This would eliminate the potential for the pilot to delay the decision to eject and recue survivability. A next-generation ejection seat such as this represents a quantum leap in assisted escape system technology. Aircrew survivability will be significantly increased owing to the seat’s greatly expanded flight envelope. Ejection seat manufacturers and their customers are already running research and development projects in this domain. Such efforts are also looking at reducing the radar reflectivity of the seat once it leaves the aircraft, leading to a ‘stealthy’ ejection. The next-generation ejection seat will have an expanded supersonic flight envelope, enhanced windblast protection, a ‘stealthy’ structure, more integrated digital decision control technology, and thrust-vectoring propulsion systems with attitude-stabilising and automatic terrain-avoidance capabilities. Such a system would offer fast jet aircrew a much enhanced life-saving option. Case Study On the 23 July 2010, at approximately 1215, a Royal Canadian Air Force CF18 Hornet (serial number 188738) crashed during practice for the Alberta International Airshow at the Lethbridge County Airport. The 36-year old pilot, Captain Brian Bews, safely ejected. Captain Bews, a Hornet pilot for six years, was the RCAF 2010 Demo Hornet pilot, and was from 425 Tactical Fighter Squadron based at 3 Wing, Bagotville, Quebec. He sustained three vertebral compression fractures as a result of the ejection. The incident occurred during routine aerobatic practice for the upcoming air show. While doing a transition manoeuvre to a high angle of attack 300 feet above ground level, the aircraft suffered a loss of thrust in the right engine. Bews felt the aircraft sink a little, and as he applied full power, the left engine responded normally but the right engine remained at flight idle power. The asymmetric

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condition of the aircraft caused immediate and rapid roll and yaw to the right, despite Bews’ attempts to regain control. At an altitude of only 150 feet and with the aircraft at a bank angle of 90 degrees, Bews ejected. The aircraft continued its rapid spiral descent until it impacted the ground in an extreme nose-low attitude and burst into flames. Bews landed under a fully deployed main parachute. The subsequent accident investigation revealed that the right engine malfunction was caused by a component failure in the main engine fuel control system. This prevented the engine from going beyond flight idle power when Bews applied full afterburner. The substantial asymmetric thrust between the left and right engine caused a loss of control and Bews had insufficient altitude from which to recover the aircraft. Captain Bews made a complete recovery from his injuries, and returned to full military flying duties.

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Chapter 8

Selection and Training This chapter will look at the selection and training of fast jet pilots. Fundamentally, it is difficult to predictively select the ideal future fast jet pilot. While various selection methodologies attempt to do this, the system is far from perfect, as the drop-out rate in fast jet training shows. Nonetheless, selecting the best possible candidates on the basis of current selection knowledge does offer the best way of getting the most suitable candidates into the fast jet cockpit. Appropriate and effective training can then do the rest of the task, in terms of taking that pool of suitable candidates and converting most of them into fully trained fast jet pilots, ready to assume a front-line operational role. Training is considered in the second half of this chapter, and the emphasis here will be on two parts: the basic flight training programme, from entry to operational front-line fast jet pilot, and the ongoing human factors and performance limitations training that fast jet pilots will be regularly exposed to throughout their careers. Selecting the Fast Jet Pilot Why put effort into selection? A fast jet pilot, as we have seen in this book so far, operates in a cognitively challenging and physically demanding environment, with high risks and significant pressures. Getting the right candidate to sit in the aircraft can have a major influence on whether the mission is completed successfully. The wrong pilot may be overwhelmed and unable to cope in the high-pressure risk-intensive environment of combat fast jet operations. This may make mission effectiveness more problematic, as well as risking the life not only of the pilot but also the lives of fellow fast jet pilots and even of friendly forces in the area. Fast jet training is intensive and expensive. The wrong candidate may not complete the training regime, leading to a waste of increasingly tight training funds. It can cost upwards of $1 million to train a fast jet pilot. Despite the best efforts of the selection process, there is an attrition rate during fast jet training. The USAF’s acceptable pilot training attrition rate is in the range 8–10 per cent (Carretta, 2000). Similarly, it is possible for less-than-ideal candidates to complete the training but not be an effective pilot at the operational end. Selection is conducted by most air forces, in order to try to get the best possible candidates for the fast jet role. It is important to remember that the pilot and aircraft in combination constitute a weapons system, which is a high value asset for a government. Making sure that the right candidates become fast jet pilots helps to ensure the effectiveness of that weapons system. What characteristics are

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known to be helpful for a fast jet pilot? What do they need to be able to do? Given the complexity of the operating environment, it is no surprise that the ideal fast jet candidate can be considered to have the following attributes: • • • • • •

Capacity to think rapidly and decisively Self-confidence Prepared to take risks but in a measured, calculated way Ability to multitask Possesses a cool, calm temperament while under pressure Capacity to handle complex and rapidly changing dynamic geometry in terms of air combat manoeuvring • Capability to understand and retain significant amounts of complex technical information on aircraft performance and weapons systems engagement parameters • Capacity to readily interpret the information presented on sighting and display systems in order to maintain accurate and timely situational awareness. Furthermore, fast jet pilots need to possess all the ideal characteristics that air forces set for their officers, in terms of leadership, personal qualities and military bearing. While the ability to manage themselves and their aircraft is crucial, so too is the ability to effectively manage other people and aircraft in high-risk combat environments. Both leadership and followership abilities are desirable in a fast jet pilot. Review of Selection Methodologies Selecting individuals to undergo fast jet training is a complex task. There is significant downside risk to getting the selection process wrong. To that end, most air forces will use a number of selection methodologies in order to select their fast jet training candidates. A comprehensive review of all currently available selection methodologies used by air forces around the world, particularly in terms of applicability and validity, is well beyond the scope of this book. However, a brief review of some elements of the available selection methodologies as they relate to fast jet pilot selection is useful. Initially, most air forces make the selection on the basis of military officer suitability. Since most air forces only put officers into the role of fast jet pilot, the likely candidates are first selected on their ability to make a good military officer. How air forces do this varies considerably, but in essence they are looking for candidates capable of displaying leadership under pressure, good personal discipline and military bearing. Various aptitude tests (often computer-based) are used to help make the selection decision, as well as interviews. Candidates must also have achieved a minimum educational standard for officer selection (a university degree, in most cases). Candidates must also meet a minimum set of medical and anthropometric standards for both officer and active duty pilot selection purposes. In addition to these medical tests, many air forces

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also use some form of neuropsychological testing to attempt to enhance selection accuracy. These tests can include Cog Screen, the Multidimensional Aptitude Battery (MAB), and various personality test batteries. Once the candidates have been assessed as suitable for officer training, the selection process for pilot training then becomes the next hurdle for them to overcome. Most air forces use some form of psychometric and cognitive testing to try to select the most suitable pilot candidates. There is a wide range of choice available in terms of which tests to use. Many of the tests have been developed in-house by air forces for their own particular needs. For example, the USAF uses the Air Force Officer Qualifying Test (AFOQT) and the Basic Attributes Test (BAT) to select its pilot candidates. The AFOQT, in use since 1957, is a paperbased test that assesses cognitive abilities, aviation knowledge and perception speed (Carretta, 2000). The BAT is a computer-based test battery that assesses not only cognitive ability but also psychomotor skills and risk-taking behaviour. It has been in use with the USAF since 1993 (Carretta, 2000). The USAF combines the AFOQT and BAT scores with a measure of flying experience to generate a composite score for each candidate, known as the Pilot Candidate Selection Method (PCSM) score. Does any of this actually yield positive results? In USAF experience, PCSM scores are directly correlated with success at training. The higher the PCSM score, the higher the likelihood of completing fast jet training, the higher the class ranking, and the fewer flying training hours required (Carretta, 2000). This finding in itself would tend to lend some positive weight to the notion that pilot selection testing is a worthy activity. No studies have definitively identified what might be termed the typical fast jet pilot personality. Such a phenomenon would make personality testing of pilot candidates significantly more straightforward and robust in its application than might be considered the case today. Several US studies have shown that military pilots fall into three broad personality categories (Picano, 1991; Retzlaff and Gibertini, 1988). The biggest group is task-focused, dominant and affiliative, which the researchers labelled as the ‘typical military pilot’. The other two categories included more aggressive and exhibitionistic pilots, and pilots who were more cautious, among other traits. However, these categorisations have failed to predict success in terms of fast jet pilot training (Boyd, 2005). Boyd (2005) attempted to look at this question of predictive ability of psychological testing. Through analysis of the entry MAB and personality testing results, they showed that fighter pilots tended to score higher on intelligence quotient (IQ) testing than bomber or transport pilots, but scored lower on personality traits such as agreeableness and conscientiousness. The researchers argued that these scores could be a useful adjunct in the fast jet pilot selection process, along with flight training performance. More work needs to be done in the area of neuropsychological testing, in terms of its ability to predict success in fast jet pilot training. This might help to lower the overall attrition rate for expensive fast jet training.

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Many countries use a flight screening programme as part of the selection process for pilot candidates. Otherwise suitable pilot candidates (those who have successfully passed all other stages of the selection process) are sent for this flight screening programme. The courses are designed to assess the student’s abilities, not only in terms of flying the aircraft, but also in terms of how rapidly and effectively they can learn and adapt. This is an important consideration, as most air force training pipelines require a certain number of individuals to have successfully completed their training at a certain point in the future. Students thus need to be able to keep up with the pace of instruction. Flight screening tends to be relatively short. The USAF’s Introductory Flight Screening programme is of some 25 flight training hours. The Royal Australian Air Force’s Flight Screening Program has been running since 1991, and involves a 2-week course with approximately 15 hours on the CT-4B and CAP 10 aircraft. Flights are scored, and these scores together with qualitative assessments made by the flight instructors form the basis of a recommendation for entry into RAAF pilot training. Training the Fast Jet Pilot Having selected the candidate pool, attention now turns to training. The training pipeline is designed to ensure that the air force’s particular personnel needs are met. This would usually include making sure that enough pilots are trained to cover those at the other end of the spectrum who are leaving the service. Making sure that all operational squadrons have their full complement of pilots is important, as is making sure that there are enough suitably experienced pilots to act as pilot training instructors. Any expansion in the operational workload of the air force may mean that a net increase in the pilot population needs to be made, which will only be met through training a sufficiently large number of pilots. Clearly, then, managing the training needs of an air force is a particularly significant task. Fast Jet Flight Training No two air forces train their fast jet pilots the same way. The length of training, the aircraft types used, and the training methodologies employed, all vary from one country to another. In addition, depending on individual country circumstances, the training regime may change from period to another. In some countries, there is a trend to outsource basic flight training or even the entire pilot training process. This usually involves a private company taking over training responsibility, and employing ex-military instructors to conduct the training. Since pilot training is a dynamic phenomenon and subject to change, the discussion here will be limited to the general approach to flight training, with some specific current examples. The typical approach to fast jet training is seen in Figure 8.1.

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Officer Selection

Pilot Selection

Basic Flight Screening

Officer Training School Aeromedical & Human Factors Training Combat Survival Training

Basic Flight Training Advanced Flight Training (Wings Standard)

Lead-In Fighter Training

Operational Conversion Front-Line Squadron

Figure 8.1

Fast jet pilot selection and training pipeline

After successfully completing military officer selection and pilot candidate selection (and flight screening if required), candidates are then sent for their basic officer training. After successful completion of this, they would then undergo initial aviation medicine and human factors training (discussed later) and combat survival training (involving marine, jungle and desert survival, as well as escape and evasion training). This training may occur at a later point in the training cycle, depending on the particular air force’s approach. The first step on the pilot training ladder is Basic Flight Training. This is usually conducted in a typical training aircraft, and may take up to six months. All RAAF pilots complete an initial Basic Flight Training Course, which at the time of writing is 25 weeks in duration and involves 63 hours of flight training

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on the CT-4B piston-engined trainer. The USAF flight training programme is known as Joint Specialized Undergraduate Pilot Training Program (JSUPT) which involves USAF and US Navy pilot trainees. The JSUPT primary flight training phase involves around 90 hours of flight training over a 6-month period on the T-6 Texan II advanced turboprop trainer (based on the PC-9 aircraft). In the RAF, the Elementary Flying Training programme is conducted on the Tutor T1 aircraft (based on the Grob 115E single piston-engined training aircraft). The next phase of the training involves the completion of military pilot training to ‘wings’ standard. In addition to basic flying skills acquisition, this phase of training teaches the students advanced military flight skills such as low-level navigation and formation flying. At the completion of this phase, the candidates are designated as qualified military pilots (although with no particular aircraft type or track specialisation). In the RAF, this training is done on the Tucano aircraft (an advanced turboprop trainer). In the RAAF, successful graduates from the basic flight training programme progress to No 2 Flying Training School at RAAF Pearce, where they will spend approximately 37 weeks and complete around 120 hours of flight training on the Pilatus PC-9A advanced turboprop trainer. At the successful conclusion of this primary flight training phase, the graduating pilots are selected for various aircraft streams. These include fighter/ attack, bomber, transport or helicopter (depending on the particular air force). The decision point as to what stream the graduating pilots will move to varies considerably between countries. In the RAAF, the streaming decision is made after the pilots reach ‘wings’ standard. However, there is a growing trend to stream pilots earlier in the training cycle rather than later. In the RAF, pilots are streamed to fast jets or other aircraft at the conclusion of the Elementary Flying Training programme. In the United States, pilots are streamed to fast jets, transport aircraft or helicopters at the conclusion of the primary phase of JSUPT. This process matches the preferences of the students against the USAF and US Navy needs (in terms of numbers required for each track, as well as each individual’s performance on their training, as well as more subjective elements such as military officer qualities) and students are then sent to their appropriate next training course. Irrespective of how the decision is made, pilots streamed for fast jet training will then undergo initial and lead-in fighter training courses. In the RAAF, for those selected to fly fast jets, initial and lead-in fighter training is conducted on to the BAE Hawk 127. The first phase of this involves a 14-week Introductory Fighter Course on the Hawk at RAAF Pearce with 79 Squadron. At the conclusion of this course, the next destination for the future RAAF fast jet pilot is 76 Squadron at RAAF Williamtown, where a 20-week lead-in fighter training course is conducted. This involves extensive air-to-air and air-to-ground tactics and weapons training. In the RAF, having been streamed earlier to the fast jet role, pilots will complete their training to ‘wings’ level and then move on to lead-in fighter training and tactical weapons training on the BAE Hawk advanced jet trainer. In the US, students in the fast jet stream in JSUPT undergo a period of advanced aircraft training on the twin-engined supersonic T-38 Talon aircraft. This training

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encompasses some 120 hours of flight training, over a duration of some six months. At the successful completion of this phase of their training, students can then select their preferred aircraft type (for example, F-15, F-16, F-22, and so on). The final selection is based on flight training performance, academic performance, merit, recommendations from the instructing staff and prevailing USAF needs. In recent years, the US military has combined with some NATO partners and established the Euro-NATO Joint Jet Pilot Training programme. This is designed to train NATO fast jet pilots, but many prospective USAF and US Navy fast jet pilots also receive their training under this programme. Based at Sheppard Air Force Base, Texas, it is approximately a year in duration, and involves 125 hours flight training on the T-6 followed by 135 hours on the T-38. Selection to a specific fast jet aircraft type occurs at the completion of this year-long programme. The final phase of the fast jet training process is operational conversion training. This is where the newly qualified fast jet pilot undergoes type-specific training on a particular aircraft type, and then proceeds to duty in an operational fast jet squadron. In the RAAF, the student fast jet pilot progresses to operational conversion on either the F/A-18A Hornet or the F/A-18F Super Hornet. In the RAF, pilots are sent to an Operational Conversion Unit (OCU) to complete their training and assume the role of front-line fast jet pilot, on either the Eurofighter Typhoon or Panavia Tornado. At the conclusion of operational conversion training, the pilots are now regarded as fully qualified operational fast jet pilots. It can be seen that fast jet pilot training is a long and complex process. In the RAAF, out of around 40 or so graduates of No 2 Flying Training School each year, approximately 15 are selected for fast jet operations and of those only about 10 on average will successfully complete their fast jet training and become operational fast jet pilots. In total, those individuals who make it to the RAAF’s operational fast jet squadrons will have usually spent around four years in training. Use of Flight Simulators Air forces around the world are increasingly making use of advances in flight simulation technologies to assist with the fast jet training process. The modern highfidelity flight simulator is able to offer almost unparalleled training opportunities. In the fast jet environment, the simulator usually takes the form of a type-specific and fully functioning cockpit linked to a sophisticated visual projection system (often a dome arrangement). The simulator tends to be fixed-base (that is, does not move during flight), but sometimes incorporates a so-called ‘G seat’ which uses pneumatic actuators to apply pressure to the pilot’s body in order to recreate the feeling of being pushed into the seat by the application of +Gz forces. Such cueing systems are designed to increase the fidelity of the fast jet simulation experience. The fast jet simulator does not entirely replace actual flight in the aircraft. It does afford the fast jet pilot the opportunity to build experience and familiarity with the aircraft and its systems, and a tremendous tool to develop and hone tactical

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skills in a safe and controlled environment. The simulator can be used to practise and check instrument flying skills, to manage various aircraft emergencies, or to develop weapons cueing skills with advanced helmet-mounted sighting and display systems. For the air force, it offers a significantly cheaper training option than actual aircraft flight hours, allowing the training to be more cost-effective. Modern fast jet simulators can be linked across a network such that formation flying and even air combat manoeuvring can be practised. Given this capability, there is also an increasing trend to use these flight simulators for mission rehearsal purposes. With the incorporation into the simulator of a high-fidelity terrain and navigational database, the fast jet pilot could rehearse a difficult mission (be it air-to-air or air-to-ground) in order to become familiar with the environment and the possible threats within it. Such mission rehearsal can help the fast jet pilot to prosecute the actual mission more effectively and safely. Human Factors Training Once a pilot has qualified as a fast jet pilot, the next element of training that is of interest to us here is that of human factors training. In a broad context, this training includes a number of elements, such as human performance limitations, aviation medicine, emergency procedures training and human factors training. In the context of this book, this training is worthy of some detailed description. In almost all air forces around the world that are equipped with fast jets, the pilots are regularly exposed to such training. This is done on an initial basis, then on a recurring basis. For the purposes of this chapter, it is worth looking at the general content of this training, as this will serve to highlight the complexity of the training environment that a fast jet pilot faces. Furthermore, it highlights the risks involved in their daily operations, the information load they must carry, as well as the speed with which they need to process information, especially during an emergency. Initial training is usually conducted before the pilots undertake their basic flight training. This of course makes a lot of sense, as the risks that the aviation medicine and human factors training deals with are ever-present during basic flight training. The initial aviation medicine and human factors training normally involves didactic class-room based training which explains the various physiological challenges involved in fast jet operations. Spatial disorientation, hypoxia and +Gz effects are covered, as well as vision, hearing and fitness to fly issues. Supporting this theoretical training is an increasing use of dedicated and specialised simulators, such as ejection seat trainers, altitude chambers, spatial disorientation demonstrators and high +Gz centrifuges. These devices, which are increasing in their capability, fidelity and level of sophistication, are used to give practical experience of various physiological challenges to fast jet crew, to help them recognise the issues if they were to ever face them in flight. The ejection seat trainer is designed to give them practical experience of an ejection sequence (de-rated for safety of training), information on correct posture and ejection

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procedures, as well as confidence in the ability of the system to safely get them out of the aircraft when needed. Recurrent training is done at regular intervals. In most air forces around the world, fast jet pilots undertake this recurrent training every three to five years. The recurrent training is a shorter form of the initial training, since most of the knowledge is assumed. The training tends to be type-specific, in that only information relevant to the aircrew’s current operational aircraft type is given during their refresher course. Hence, fast jet pilots receive training in high +Gz forces, ejection, and pressure breathing, while transport aircraft pilots would not receive such training. The underlying idea is that the training should be operationally relevant to the aircrew. The purpose of the recurrent training is to act as a refresher for aviation medicine and human factors knowledge in the pilots and crew, as well as to give them repeat experience in the altitude chamber, centrifuge and disorientation trainer. Refresher training is also done for other reasons, such as when a pilot converts to a new aircraft type (for example, a transport pilot becoming a fast jet pilot), or after a period of non-flying (as in returning to flying after time spent in a ground-based role, or after recovery from an extended illness). The subject matter for the training (both initial and recurrent) covers aviation physiology, medicine and human factors. Subjects covered include altitude physiology and hypoxia, spatial disorientation, the effect of pressure change on the human body (including barotraumas and decompression illness), thermal stress, motion sickness, vision, noise, vibration, ejection and survival, fitness to fly, life support equipment, human factors (including fatigue, information processing, perception, memory, communication and crew resource management). Depending on the equipment used in a particular air force, instruction might also be given in night vision and the correct fitting and use of night vision goggles. The instructors for this training are usually highly qualified aviation medicine specialists. These are military medical officers who have received additional specialised training in aviation medicine, physiology and human factors. Many of them are also pilots (usually civilian, sometimes military), and in general they will have spent time as active duty aviation medicine specialists on flying bases in support of military flight operations. Other instructors may be aircrew who have received specific training as aviation physiology instructors, and perform this role in between tours of duty as operational aircrew. The training is usually conducted at the particular air force’s aviation medicine institute or training centre. Most air forces have a centralised system, where there is only one aviation medicine institute or training centre, to which the aircrew will travel when they require the training. For example, aviation medicine training in the UK is carried out at the RAF Centre of Aviation Medicine at RAF Henlow, Bedfordshire. This centre was created out of the combination of the former RAF Institute of Aviation Medicine at Farnborough, and the RAF Aviation Medicine Training Centre at RAF North Luffenham. In addition to aircrew aviation medicine and human factors training, these aeromedical centres are also involved

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in research activities, life support equipment test and evaluation, and determining fitness to fly of aircrew. The aviation medicine and human factors training requirements (in terms of content and frequency of training) are typically stipulated in various regulations and guidelines for a specific country. NATO countries conduct training for their aircrew in accordance with a standardised NATO policy, known as STANAG 3114 Ed 8 (2006) which deals with aeromedical training of flight personnel. In general, despite the various guidelines and regulations around the world, most countries tend to do quite similar training for their fast jet aircrews. It is now worth looking at the various components of this training, and what the purpose of such training is. Ejection seat training The ejection seat remains a vital life-saving device for pilots of high performance aircraft. For pilots who operate ejection seat-equipped aircraft, appropriate training is vitally important. As was seen earlier, many air forces conduct basic flight training on relatively sophisticated aircraft, such as the T-6 and the PC-9, which are equipped with ejection seats. So, it stands to reason that ejection seat training should be done before pilots go to flight operations on ejection seatequipped aircraft. Ejection seat training involves familiarisation with the ejection seat, its various components and systems, and the manner in which it operates. In so doing, a pilot will become familiar with this life-saving piece of aircraft equipment and gain confidence in its ability to safely extract the pilot from a life-threatening in-flight aircraft emergency. Proper training in the correct ejection technique (particularly the required ejection posture) can significantly reduce the risk of injury. To conduct the training, many air forces will supplement a lecture on the seat, systems and technique with practical experience on an ejection seat training rig. This usually involves a standard ejection seat fitted to a pneumatic firing system which when initiated will give the student a de-rated ride up a set of rails. Some modern ejection seat training rigs combine a cockpit mock-up with sensors that determine whether the pilot is in the correct posture. If the correct posture is not recognised by the sensors, the seat will not fire. This helps reinforce to the student the importance of correct posture. Spatial disorientation training Many air forces use some form of specialised spatial disorientation demonstration device, which in many cases is a single-person motion-based flight simulator. The simulator is able to demonstrate the various visual and vestibular illusions that a pilot might experience in flight. Furthermore, the simulator allows the pilot to recognise the particular illusion and to practise the safe recovery from the illusion by flying themselves out of the illusion. The spatial disorientation demonstrator typically has a generic cockpit, and can be quickly converted by the instructor to either fixed-wing or rotary-wing flight models. The nature of the demonstration training in the simulator depends

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on how this device has been integrated into the overall training programme for a particular air force. Many of the illusions are pre-programmed, and the pilot will passively experience the illusion. In other cases, the pilot must fly certain elements of the programme in order to achieve the illusion. In yet other cases, a free flight mode can be used in which the pilot simply flies under the direction of the outside instructor, who can then alter certain variables in order to develop the illusion (for example, create a sloping cloud base, or make the runway slope downwards, or direct the pilot to make a head movement in order to develop the Coriolis illusion). Experiencing disorientation and how powerful some of the illusions can be is of tremendous training potential. This sort of demonstration shows just how easily a normal pilot can develop significant disorientation in certain conditions on a given day. Furthermore, by allowing the pilot to experience the illusion, and then effectively recover from it through correct use of the instruments, this training gives the pilot confidence in their ability to recognise and deal with disorientation if it should occur in flight. Awareness training like this is invaluable from a flight safety perspective. Hypoxia training Most air forces around the world provide altitude training for their aircrew. This training is designed to make individual aircrew members aware of their particular signs and symptoms of hypoxia. These signs and symptoms tend to be consistent in a given individual. While they may vary from one person to the next, for a given person the symptoms tend to be the same every time they become hypoxic. The objective of such training is therefore to increase the aircrew’s awareness of hypoxia, so that they might be able to recognise it should it occur to them during the course of a mission. If they can recognise that hypoxia is occurring, they can then take steps to rectify the problem before it is too late. Such steps include descent to a lower altitude (and thus into air containing more oxygen), switching to 100 per cent breathing oxygen, and pressure breathing. Failure to appreciate the signs and symptoms of hypoxia can be fatal. For the purposes of demonstrating the effects of hypoxia, most air forces use a hypobaric chamber. These devices consist of a large main chamber in which the students sit (up to 12 aircrew at a time). The atmospheric pressure in this chamber is altered by a series of vacuum pumps to produce the desired altitude. Most chambers can simulate altitudes well above 50,000 feet (up to 100,000 feet in many cases). The chambers are also generally able to produce a rapid or explosive decompression, to simulate loss of cockpit pressure or loss of the canopy, for example. This training allows aircrew to become familiar with the fundamental features of decompression, and what it feels like. It also allows them to practise some of the protective techniques that they must learn, such as positive pressure breathing for aircrew operating at altitudes over 40,000 feet. The rate of ascent and descent of the chamber’s altitude is generally computer-controlled in modern chambers.

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The two major aspects of chamber training are demonstration of hypoxia and exposure to rapid decompression. As was seen in Chapter 2, hypoxia can occur for many reasons, such as failure of either the cockpit pressurisation system or personal oxygen system. The development of hypoxia in aircrew is often an insidious process, and for the untrained individual it can pass un-noticed and unrecognised. With no corrective actions being carried out, such a situation is likely to result in unconsciousness and the subsequent loss of the aircraft and its crew. This can occur in a very short space of time. For example, at an altitude of 25,000 feet the time available for hypoxia to be recognised and appropriate corrective action undertaken is in the order of three to five minutes. This time reduces to 10 to 20 seconds at 40,000 feet. Practical experience of hypoxia for fast jet crews is very important, as they become familiar with their own particular signs and symptoms of hypoxia. This allows them to recognise the onset of hypoxia and take corrective action if such a problem occurs during a mission. Hypoxia demonstrations normally take place at an altitude of 25,000 feet. This altitude is the most practical one for this purpose, as hypoxia symptoms tend to be obvious and occur relatively quickly at this altitude. On the other hand, the lack of oxygen at this altitude is not as severe as at higher altitudes where unconsciousness would occur in less than a minute. During their hypoxic experience aircrew usually are required to complete a series of relatively simple cognitive tasks in order to show how hypoxia affects the functioning of the brain in subtle yet important ways. These often consist of mathematical problems, or a checklist of items that need to be looked up from aeronautical publications (runway headings at a particular airfield, tower radio frequencies, and so on), with the answers being written down on a sheet of paper. In some countries, such as Germany, students use a lap-top computer-style instrument to complete the cognitive tasks. Whatever the nature of the task, the important aspect is that they become more difficult with the progression of hypoxia. Decompression training gives the aircrew an appreciation of what to expect if they suddenly lose cockpit pressurisation in their aircraft during a mission, and for fast jet crews this decompression training allows them to practise pressure breathing techniques (essential for survival at altitudes above 40,000 feet). Most countries use two typical fast jet chamber profiles, in order to give experience of hypoxia as well as pressure breathing. The first profile is the most common. It is a standard chamber training profile to 25,000 feet. The initial climb from ground level to 8,000 feet (where a brief equipment check is usually conducted) is made at 4,000 feet per minute. Rapid decompression from 8,000 to 25,000 feet is then carried out. This simulates sudden loss of cockpit pressurisation, and generally only takes a few seconds. Hypoxia training is then done at 25,000 feet. This approach has the advantage of limiting the overall altitude exposure of the students (in order to protect them from decompression illness) while at the same time giving them a sufficiently hypoxic environment such that they are able to recognise the development of the signs and symptoms of hypoxia.

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The other chamber training profile used involves a standard climb (at around 4,000 feet per minute) to 18,000 feet (after an ear and equipment check at 5,000 to 6,000 feet in many countries) and then a rapid decompression to 45,000 feet. Pressure breathing takes place for a brief period (approximately 20 to 30 seconds) before descent at 10,000 feet per minute to 25,000 feet for the hypoxia demonstration. This profile is used by the Royal Air Force for aircrew flying highlevel aircraft such as the Tornado F3. The Canadian Forces use a variation on this profile for their fast jet crews, with a decompression to 43,000 feet and hypoxia demonstration at 30,000 feet. In recent years, some air forces have adopted a normobaric approach to altitude training. This ground-level training uses a reduced oxygen method to generate hypoxia, rather than a low- pressure environment as in a hypobaric chamber. The pilots using such systems breathe a percentage of oxygen less than the normal 21 per cent in order to achieve a physiologically equivalent altitude (for example, they would breathe 15 per cent oxygen to physiologically be at 8,000 feet, and 7 per cent oxygen for 25,000 feet). Such systems are being increasingly looked at as an alternative to traditional chamber training, as it removes the potential for decompression illness (due to low pressure exposure) and also allows the hypoxia training to be conducted in a flight simulator. The US Navy has been using such reduced oxygen breathing systems for the last several years, particularly for refresher hypoxia training (Artino et al., 2006; Artino et al., 2009; Sausen et al., 2003). One of the key advantages for fast jet crews undertaking such training is that it allows them to experience hypoxia in ‘mask-on’ conditions, as they would during actual flight. This makes the hypoxia training more practically relevant. Altitude training such as outlined above is a critical component of the overall training of modern military aircrew. Awareness of the ever-present hazards of hypoxia and decompression are key elements in ensuring survival in the hostile environment of flight. There is evidence that this training does make a difference (Cable, 2003; Johnston et al., 2012; Woodrow et al., 2011). A Royal Australian Air Force study of in-flight hypoxia incidents, covering the period 1990 to 2001, found that in 76 per cent of cases the affected aircrew were able to recognise their symptoms of hypoxia as a direct result of their previous altitude chamber training experience (Cable, 2003). Centrifuge training As discussed in Chapter 3, the modern human centrifuge is a sophisticated device able to effectively reproduce the high +Gz environment of the fast jet in a simulated, safe and controlled manner on the ground. Most air forces that operate fast jets either have their own human centrifuge or send their pilots for training on a third-party centrifuge (usually under some inter-country Defence cooperation agreement). Given its capability, the centrifuge is the perfect tool for a whole host of training and research applications. For example, in some countries it is used as part of the screening process for pilot candidates. The centrifuge can be used

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to test for relaxed +Gz tolerance, enabling those candidates with naturally poor +Gz tolerance to be selected out. Combined with physiological monitoring, the centrifuge can be used to determine candidates with poor cardiovascular response to +Gz inputs, and symptoms at low +Gz levels (for example, G-LOC at +3 Gz). Typically, a low G onset rate is used (in the order of 0.1 G/sec). Only a small number of countries use the centrifuge for such pilot screening purposes. In most countries that use centrifuge training, it is an integral part of initial and refresher aeromedical training. There are several aims involved with such centrifuge training, including recognition of+Gz-induced symptoms (such as grey-out and black-out), to develop an effective and efficient anti-G straining manoeuvre, and to develop confidence in the ability of fast jet pilots to tolerate high +Gz levels. In some countries the centrifuge is also used for qualification purposes, where (for example) pilots must be able to successfully tolerate +9 Gz for 20 to 30 seconds before being sent for F-16 training. The centrifuge can also be used for +Gz tolerance testing for individual pilots returning to flying (for example, after illness), air combat tactics training, dynamic flight simulation, testing of new anti-G equipment and applied acceleration physiology research. The basic parameters of a human centrifuge are interesting. The centrifuge typically has an 8-metre arm, with a gondola for the human occupant at one end. The drive system is usually underground. The gondola contains either a generic or a type-specific cockpit. The type-specific cockpit involves a highfidelity fast jet cockpit (including non-operational ejection seat), a sophisticated aircraft flight model, and comprehensive out-the-window visual displays (using accurate topographical and navigation databases). This latter situation is often termed Dynamic Flight Simulation (DFS). DFS combines high-fidelity full flight simulation with sustained +Gz capability, and provides a much more realistic centrifuge training experience for the pilot. The gondola usually has a number of active electrically powered axial drives, for movement in pitch and roll. These ensure that the applied G is in the correct axis, while also helping to dampen out adverse translational G inputs due to the rotation of the main arm. To achieve a high-fidelity training solution, it is important to have very small latency parameters for the motion environment of the centrifuge, in terms of control response and visual system response. These latency periods for most modern centrifuges are typically less than 100 milliseconds. The centrifuge can be used with either pre-programmed profiles or full active control profiles. Typical passive profiles include the Gradual Onset Run(GOR), where the centrifuge is taken to a peak of +9 Gz at an onset rate of +0.1 Gz per second, and the Rapid Onset Run (ROR), where the centrifuge is taken to a high +Gz level (usually +7 to +9) at an onset rate of +6 Gz per second. Either or both of these runs can be used for qualification purposes, where the peak +Gz must be tolerated for a given time interval. The accepted standard used by most air forces (in accordance with NATO Standardisation Agreement (STANAG) 3827) is successful tolerance of + 7 Gz for 15 seconds on a ROR profile, while wearing an

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anti-G suit and performing an anti-G straining manoeuvre (Gillingham, 1987). For aircraft capable of sustaining +9 Gz, this value is used as the standard. The GOR is often used by many air forces to determine the so-called resting +Gz tolerance of an individual. Simulated air combat manoeuvring (SACM) profiles can also be used. These profiles involve a series of repetitive, alternating +4.5 and +7 Gz peaks (or +4.5 and +9 Gz), usually with fatigue being used as an end-point (Tong et al., 1998a; Whinnery, 1982). The time that a pilot is able to tolerate the SACM profile is measured. Active control profiles involve ‘man-in-the-loop’ control, where the full capabilities of DFS are exploited. In these profiles, the pilot flies the centrifuge like they would the aircraft. The pilot therefore generates the +Gz load, according to the demands of the mission they are flying. This might involve such activities as target chasing, formation flight or air combat manoeuvring. DFS thus gives tremendously powerful training opportunities. The centrifuge can then be used for several advanced flight training purposes, such as mission rehearsal and tactical flight training. NVG training In air forces where fast jet pilots use night vision goggles, the aeromedical training usually involves specific training for this vision-enhancing technology. The training usually takes the form of comprehensive didactic training on the visual system, the challenges of night operations, how NVGs work, how to correctly fit and focus NVGs, and how to maximise their effective use in flight. The didactic training is often supplemented by practical training, which involves practice in the fitting and focusing of NVGs, and demonstrations using a light bar (which can demonstrate various limitations of normal and night vision) and a terrain board. The terrain board consists of a scaled-down depiction of generic terrain, usually encompassing various topographic features such as lakes and rivers, roads, towns and mountains. Various lighting options are included, which are NVG-compatible. Through careful manipulation of the azimuth and elevation of the light, various shadow effects and terrain-based illusions can be created and viewed through the NVGs. This training gives pilots valuable information on both the capabilities and limitations associated with using NVGs.

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Index

A-10, 13, 51 Abdominal wall, 45 Abscess, 18 Absolute incapacitation period, 39, 40 Acceleration, 11, 16, 29, 33–37, 42, 44, 47, 48, 52–57, 68, 102, 128 applied, 33, 34, 35, 128 atelectasis, 29, 42 environment, 16, 34, 48 ACM, 7–9, 11, 29, 33, 35, 41, 43, 44, 55, 58, 61, 116, 122, 129 Activated carbon, 76 Active detection, 87 electronically scanned array, 87 Actuation system, 6 Adrenalin, 42 Advanced Short-Range Air-to-Air Missile, 92 technology G-suits, 72 Adversary aircraft, 10, 41, 82, 84, 86, 89 Aerodynamic, 8, 9, 16, 17, 35, 69 AFOQT, 11, 117 Afterburner, 54, 113 After-image, 94 Aggressiveness, 40 Agility, 2, 3, 6, 9, 16, 61, 83, 94 AGSM, 11, 42, 45–48, 129 Aileron, 84 Aiming reticle, 90 Air combat manoeuvring, See ACM dominance, 1, 11, 16 Force Officer Qualifying Test, See AFOQT superiority, 1, 6, 11 Airborne early warning and control, 6, 81, 95 warning and control system, 15, 96 Aircrew

equipment integration, 7, 65, 78 services package, 30 Airframe, 88 Air-to-air, 3, 4, 7, 13, 14, 16, 82, 84, 90, 92, 120, 122 Air-to-ground, 13, 14, 84, 92, 120, 122 Alcohol, 24, 43, 44, 59 A-LOC, 38, 45, 47 All-aspect, 3, 4, 5, 7, 16 Alpha, See AOA Altitude chamber, 122, 123, 127 misperceptions, 57 threshold, 22 training, 125 Alveoli, 42 Amnesia, 38, 40 AMX, 13 Analogue, 83, 85 Angle of attack, See AOA Angular acceleration, 35, 53, 55, 56, 57 accelerometers, 52 motion, 52 Ankle, 53 ANSI Z-90, 68 Anthropometric standards, 116 Anthropometry, 65, 77 Anti-diuretic hormone, 42 Anti-G countermeasures, 44 straining manoeuvre, See AGSM suit, See G-Suit system, 65 valve, 11, 30, 45, 73 Anxiety, 40 AOA, 8, 9, 16, 47, 48, 90, 112 Apathy, 38 Approach, 12, 13, 15, 49, 54, 59, 63, 87, 89, 95, 96, 118, 119, 126, 127

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Aptitude tests, 116 Aramid polymer, 66, 67 Argon, 17, 29 Arm pain, 74 Arms, 14, 36, 40, 75, 102 Arrhythmias, 18, 42 Arterial baroreflex, 44 pressure, 37 Arterio-venous pressure, 46 Atmosphere, 17, 75, 88 Atmospheric pressure, 17, 18, 25, 30, 125 Attack and Identification, 96 aircraft, 5, 12, 15 definition, 12 phase, 7 Attention, 62, 75, 86, 94, 95, 110, 118 getting devices, 86 Attitude, 11, 16, 49, 54, 56, 58, 60, 63, 82, 89, 90, 92, 95, 111, 112, 113 Attrition, 115, 117 Auditory, 23, 38, 89, 95 Auto-GCAS, 60 Autocannons, 13 Automatic Ground Collision Avoidance Systems, 60 terrain avoidance, 112 Automation, 95 Autopilot, 31, 58, 60, 84, 87 Autothrottle, 84 Aviation medicine, 17, 61, 107, 119, 122, 123, 124 Avionics, 1, 3, 4, 6, 26, 83 Awareness training, 21, 25, 61 Balance organs, 51, 53 Ballistic, 100, 102 Barodontalgia, 18 Barometric, 18 Barotrauma, 17, 19, 27, 28, 29 Baroreflex, 44 Barostatic time release unit, 99, 100, 102, 103, 109 Basic attributes test, See BAT fighter manoeuvres, 4, 7, 10

flight training, 119 BAT, 11, 117 Bayonet, 71 Beacons, 110 Bends, 30 Beyond visual range, 7 Binocular, 93 Biodynamic, 69, 96 Biological signals, 62 weapons, 62, 65, 76 Bird-strike, 68, 71 Blackhole approach, 58 Black-out, 37, 43, 128 Bleed air, 26, 27, 29, 45 leak detection, 27 Blood, 18, 20, 22, 24, 30, 36, 37, 38, 39, 40, 42, 44, 45, 46 flow, 39 pressure, 37 Boeing, 85, 92 Boresight, 4–6, 92 Boyle’s Law , 18, 19, 30 Brain, 22, 36, 38, 39, 40, 46, 53, 54, 57, 59, 61, 126 Break-off illusion, 58 Breathing, 17, 25, 27, 28, 29, 30, 42, 46, 70, 71, 72, 73, 74, 76, 123, 125, 126, 127 breathing system, personal, 17, 25, 73, 76 cycle, 73 Britain, 97, 98 Bubble, 19 Cameras, 88 Camouflage, 65 Canada, 51, 58 Canadian Forces, 11, 50, 51, 73, 127 Canard, 16 Cannon, 3, 4, 13, 15 Canopy, 27, 68, 70, 77, 100, 101, 102, 108, 109, 125 breakers, 77, 100, 102, 108 CAP, See Combat Air Patrol CAP 10, 118 Capacitance, 45 CAPTOR, 87 Carbon

Index dioxide, 74 monoxide, 24 Cardiac arrhythmias, 42 contractility, 44 Cardiovascular, 38 adaptation, 44 system, 36, 37, 44, 48 Catapult, 77, 94, 100, 102, 106 Catecholamine, 42 CBRN, 65, 75, 76 Centre of gravity, 69 Centrifugal force, 33, 34 Centrifuge, 38, 47, 79, 122, 123, 127, 128, 129 training, 47 Centripetal force, 33 Cerebral function, 38 CFIT, 49, 57, 60 Chaff, 11, 84 Chamber training, 21, 126, 127 Channelised attention, 58 Chemical weapons, 65, 76 Biological, Radiological, and Nuclear warfare, See CBRN Chemoreceptors, 22 Chest cavity, 18, 46 pain, 18 counterpressure garment, 73 Chinstrap, 68, 69 Circulation, 24, 39, 46 Class A accidents, 51 Close Air Support, 14 Closing phase, 7 Closure rate, 7, 9, 90 Cockpit, 9, 15, 17, 19, 22, 23, 25–29, 31, 36, 47, 55, 62, 65, 68, 70, 72, 74–78, 81–85, 88, 89, 90, 92, 93, 94, 96, 104, 108, 115, 121, 124, 125, 126, 128 pressurisation, 17, 25, 26, 27, 28, 29, 65, 126 pressurisation systems, 65 Cog screen, 117 Cognitive function, 20, 37, 82

149

impairment, 22, 23, 24, 38, 75 Cold, 19, 25, 31, 74, 75, 78, 102, 109 Combat Air Patrol, 11, 12 Command ejection, 101 Communication system, 67 Communications, 12, 14, 15, 19, 66, 67, 69, 71, 89, 123 Compensatory stage, 23 Compressor, 26, 45 Computer systems, 86 Conditioning programmes, 41 Confusion, 23, 35, 39, 40, 95 Contrast, 15, 21, 57, 58, 67, 93, 105 sensitivity , 22 Control authority, 16, 47 column, 2, 47, 54 laws, 47 Controlled Flight Into Terrain, See CFIT Convulsions, 40 Coriolis, 51, 56, 57, 125 Cortisol, 42 Cough, 30 Counterpressure, 73 Crew coordination, 15, 105 resource management, 123 Critical judgement, 23 stage, 23 Cross check, 63 coupled stimulation, 57 Cruise, 26, 54 CT-4B, 118, 120 Cyanosis, 23 Dalton’s Law, 17 Dark adaptation, 22 night take-off, 54 Data links, 83 Database, 89, 95, 122 DCI, 11, 17, 27, 30, 123, 126, 127 Death, 17, 18, 20, 23, 77, 97, 98 Decision, 7, 22, 75, 96, 104, 105, 112, 116, 120 making, 22, 75

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Decompression, 125 illness, See DCI Degraded visual environment, 54, 57 Dehydration, 24, 43, 44 Denial, 11, 40 Density, 36 Depth perception, 94 Depressurisation, 27, 28 Detachment, 58 Detection, 6, 7, 12, 23, 27, 87, 88, 89, 95 systems, 89, 95 Diaphragm, 42, 45 Differential pressure, 25, 26, 27 Digital, 3, 6, 16, 83, 86, 95, 96, 99, 111, 112 Display Indicators, 11, 84 flight control, 16, 83 signal processing, 6 Direct voice input, See DVI Disengagement, 6 Disorientation, 50, 54, 55 Display systems, 81 Displays, 82, 83, 84, 85, 86, 87, 88, 89, 91, 94, 95, 96, 128 Dissimilar ACM, 11 Dissociation, 20, 40 Distraction, 51 Disturbance stage, 23 Dizziness, 19, 23 Doppler, 2, 87 Drag, 9, 86, 102, 110 Dream, 40 Drogue, 100, 102, 109 Drowning, 110 DuPont Corporation, 66 DVI, 11, 96 Dynamic Flight Simulation, 128, 129 overshoot, 77, 108 Ear, 17, 18, 19, 27, 29, 51, 52, 67, 109, 127 drum, 19 Ebullism, 17, 31 ECM, 11, 87, 89, 96 Ejection, 16, 28–30, 36, 48, 63, 65, 68–71, 74, 75, 77, 78, 94, 97–108, 110–112, 122–124, 128 envelope, 77, 78, 105 fatal, 105

gun, 102 injuries, 106 outcomes, 103, 104 seat, 28, 30, 36, 65, 68, 70, 74, 75, 77, 78, 97, 98, 99, 100, 101, 102, 106, 108, 111, 112, 122, 124, 128 seat training, 124 seats, 48, 77, 97, 98, 99, 101, 103, 107, 124 sequence, 99, 105 Ejections, 69, 78, 97, 98, 101, 103, 105, 107, 110, 111 low-level, 105 multiple, 105 Electromagnetic spectrum, 88, 93 Electronic countermeasures, 6, 11, 87 Electro-optical, 6, 14, 93 Emergency, 11, 19, 26, 27, 28, 29, 30, 71, 76, 78, 79, 86, 94, 97, 98, 100, 102, 104, 105, 106, 109, 111, 122, 124 Emissions, 6, 86 Energy management, 8, 82 state, 8, 9, 10, 16 Engagement, 4, 6, 7, 8, 9, 10, 11, 14, 16, 44, 82, 84, 88, 90, 91, 116 Environmental conditioning system, 26 Escape, 9, 19, 36, 74, 78, 79, 97, 98, 99, 111, 112, 119 Euphoria, 22, 23, 38, 40 Eurofighter, 2, 29, 30, 73, 85, 87, 88, 95, 96, 121 Eustachian tube, 19 Exhaust outlet, 19 Extended coverage G-suits, 73 Eye, 36, 37, 56, 67, 70, 84, 91, 93, 94, 103, 109 F/A-18, 1, 3, 9, 13, 21–23, 26–28, 31, 35, 40, 41, 84–86, 88, 92, 121 F2H-1, 98 F-4, 2, 40 F-15, 2, 3, 13, 28, 41, 45, 51, 63, 88, 92, 121 F-16, 2, 3, 13, 28, 35, 40, 45, 48, 51, 69, 92, 121, 128 F-22, 3, 29, 85, 87, 92, 95, 121 F-35, 3, 30, 85, 87, 88, 91, 95, 96

Index F-80, 2 F-86, 2, 98 F-100A, 108 F-104, 2 F-105, 2 F-117, 51 Face, 18, 19, 29, 36, 46, 59, 67, 71, 76, 77, 108, 122 False horizon illusion, 55, 58 Fast jet training, 115, 116, 117, 118, 120, 121 Fatigue, 22, 23, 24, 43, 44, 46, 50, 59, 68, 69, 94, 123, 129 Field of regard, 93 of view, 52, 57, 58, 61, 88, 92, 93 Fighter definition, 1 generations, 2 sweep, 11, 12 Filter, 76 Firing handle, 100, 101, 102 Firing position, 7, 9 First aid, 110 Fitness, 24 to fly, 122, 123, 124 Flailing, 40 Flares, 11, 84, 110 Flight control systems, 14, 15, 47, 83 display, 51, 83, 89 envelope, 47, 112 helmet, See helmet instruments, 50, 61, 62 path, 15, 33, 58, 59, 89 screening, 118, 119 simulation, 47, 128 simulator, 121, 124, 127 suit, 65, 66, 72, 74 training, 115, 117, 118, 119, 120, 121, 122, 124, 129 FLIR, 87, 88, 92, 95 Floatation, 74 Fly-by-wire, 83 Flying boots, 65, 74 gloves, 65 Force multipliers, 12, 81, 93

151

Formation flying, 120, 129 Forward air control, 14 looking infra-red, 87 Fracture, 106, 107, 108, 111, 112 French Air Force, 73 Frequency, 87, 124 Friendly fire, 14, 87 Functional buffer period, 39, 44 reach, 77 Fuse, 6 G

induced loss of consciousness, See G-LOC loads, 34, 36–39, 43–46, 67, 70, 73, 94, 97, 102, 108, 129 measles, 42 tolerance, 37, 43, 44, 46, 72, 128, 129 suit, 42, 44, 45, 48, 65, 66, 72, 73, 77, 85, 129 time tolerance curve, 44 Gastrointestinal tract, 18, 19, 27 GCI, 11, 12 Gentex Corporation, 67 Geometry, 5, 7, 8, 10, 15, 48, 82, 116 Germany, 97, 126 G-excess illusion, 57 Giant hand illusion, 58 Glare, 67 G-LOC, 38, 39, 40, 41, 43, 44, 45, 47, 48, 65, 73, 128 Global positioning system, 14 Glottis, 45 Gondola, 128 GPWS, 86 Graveyard spin, 56 Gravitational field, 36 Gravity, 11, 15, 33, 34, 35, 48, 52, 53, 67, 69, 94 Grey-out, 37, 43, 128 Gripen, 88 Grob 115E, 120 Ground attack, 13, 83 impact, 50, 56, 57, 58 Moving Target Identification, 87

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proximity, 57, 86 controlled intercept, See GCI Guidance, 2, 4, 6, 14, 15, 59, 89 Guns, 3, 4, 7, 8, 9, 13, 58, 84 tracking, 3 Gunsight, 89 Gz limits, 35 Haemoglobin, 20, 24 Haemorrhaging, 109 Haldane’s critical saturation ratio, 30 Hands On Throttle And Stick, See HOTAS Harness, 100, 101, 102, 103, 108, 109, 110 Hawk, 13, 40, 120 Head, 4, 5, 35, 36, 37, 39, 41, 44, 46, 48, 53, 55, 56, 57, 67, 68, 69, 70, 71, 76, 77, 84, 90, 91, 92, 93, 94, 100, 102, 103, 106, 108, 109, 125 ache, 22 injury, 68 box, 77, 103 Heading, 31, 55, 89 Head-Up Display, See HUD Hearing, 23, 38, 67, 89, 122 Heart, 18, 36, 38, 44, 45, 46 rate, 44 Heat signature, 4, 6, 88 stress, 75 Height misperception, 58 Heinkel, 97 Helicopter, 17, 74, 93, 111, 120 Heliograph, 110 Helmet, 3, 6, 41, 48, 54, 60, 65, 66, 67, 68, 69, 70, 71, 76, 77, 84, 85, 86, 87, 88, 89, 91, 92, 93, 94, 95, 96, 103, 106 Helmet-mounted cueing systems, 3 Helmet-mounted displays, See HMD Helmet vehicle interface, 92 Helmet-mounted display and sighting system, 6, 69, 89, 91, 94, 95, 96, 122 Helmet-mounted equipment, 68, 69 Henry’s Law, 30 HMD, 54, 60, 84, 86, 92, 94, 95 Horizontal situation display, See HSD HOTAS, 2, 3, 84

HSD, 84, 85 HUD, 2, 3, 60, 84, 85, 86, 88–91, 95 Human factors, 1, 4, 16, 22, 61, 69, 75, 81, 87, 89, 96, 115, 119, 122–124 Human–machine interface, 81, 83, 96 Hydrostatic force, 36, 38 pressure, 36 Hypobaric chamber, 21, 27, 125, 127 Hyperventilation, 22 Hypothermia, 27, 74, 75 Hypoxia, 5, 8, 17, 18, 19, 20, 21, 22, 23, 24, 25, 27, 28, 29, 30, 31, 43, 65, 71, 102, 109, 122, 123, 125, 126, 127 Hypoxic ventilatory response, 22 Identification Friend or Foe, 87 Illness, 11, 17, 24, 25, 27, 28, 30, 59, 123, 126, 127, 128 Illusions, 51, 52, 54, 57, 58, 59, 62, 92, 124, 125, 129 Image intensification, 93 IMC, 54, 61, 62 Immersion suit, 65, 74, 75, 78 Immunological responses, 30 Impact attenuation, 68 energy, 67 protection, 66, 67, 68, 69 Incapacitation, 23, 39, 40, 43, 48 Indian air Force, 62, 77, 111 Indifferent stage, 23 Individual variation, 24, 25, 43 Inertial navigation, 14 Inertial vectors, 35 Information processing, 16, 23, 60, 82, 83, 90, 123 Infra-red, 2, 4, 5, 6, 14, 87, 88, 93, 95 Infra-red search and track, See IRST Injury, 41, 68, 69, 77, 97, 101, 103, 106, 107, 108, 109, 110, 112, 124 Inlet valve, 72 Inspiration, 42, 46 Instructors, 118, 123 Instrument flying, 122 landing system, 59

Index meteorological conditions, See IMC panel, 83 Instrumentation, 2, 60, 85 Instruments, 55, 60, 62, 85, 125 Insulation, 75 Integrated Control Panel, 85 Intelligence Quotient, See IQ Intercept trail, 12 Interception, 1, 11, 12 Interdiction, 11, 14 Intestine small, 19 Intrathoracic pressure, 45, 46 IQ, 117 IRST, 6, 87, 88, 96 Isometric, 45 J-10, 88 J21, 98 JHMCS, 69, 70, 92, 94 Joint Helmet Mounted Cueing System, See JHMCS Joint Specialized Undergraduate Pilot Training, See JSUPT Joints, 53 JSUPT, 120 Judgement, 22, 23, 40, 75 Junkers, 97 Kevlar, 67 Kill solution, 4, 7 Knee, 53 Knife-edge illusion, 58 Lag rolls, 10 Landing, 30, 31, 54, 58, 59, 68, 106, 109 LANTIRN, 88 Laser, 6, 14, 15, 67, 87, 88, 89 protection, 67 Laser warning, 87 receiver, 89 Lateral axis, 35 LCD, 84, 85 Lead turn, 10 Leadership, 15, 116 Leans, 51, 55 Legs, 36, 77, 102, 108

153

Life preserver, 74 support equipment, 22, 62, 65, 66, 71, 75, 76, 77, 78, 79, 124 Ligaments, 53 Limb restraint, 99 Limbs, 36, 45, 77, 94 Linear acceleration, 54 accelerometers, 52 Liquid cooling garment, 65, 75 crystal display, See LCD oxygen, 28 Liver, 109 Longitudinal axis, 35 Look down, shoot down, 87 Loss of consciousness, 17, 18, 20, 21, 23, 37, 38, 39, 43, 65 Low-differential pressurisation system, 27 Low-level, 18, 24, 55, 58, 61, 87, 105, 106, 112, 120 Low Probability of Intercept, 87 Lungs, 18, 27, 29, 42, 46, 72, 73 MAB, 117 Macchi, 21, 107 Mach, 16, 90, 108 Man-in-the-loop, 47, 129 Manoeuvring, 7, 8, 11, 16, 29, 33, 35, 36, 41, 43, 45, 53, 54, 55, 58, 61, 69, 70, 84, 90, 91, 94, 116, 122, 129 phase, 7 Manual override, 100, 101, 103, 109 Martin-Baker, 98, 99 Mask, 19, 21, 22, 29, 31, 41, 48, 65, 67, 70, 71, 72, 76, 111, 127 Me-262, 2 Medications, 59 Memory, 22, 23, 38, 83, 123 Mental impairment, 37 Meteor, 98 MFD, 84, 85 Microphone, 67, 71 Microprocessor, 99, 111 Middle ear, 18, 19, 29 Mig-15, 2

154

Flying Fast Jets

Mig-17, 2 Mig-21, 2 Mig-29, 2, 88, 101 MIL-H-87174, 68 Miniature detonating cord, 102, 108 Mirage 2000, 2, 13 Mismatch, 42, 50, 56 Missile approach warning system, 87, 89 radar-guided, 3, 4, 5, 6, 14, 86, 87, 88, 89 warning system, 89 Missiles, 2–7, 9, 13–16, 84, 86, 88, 89, 92, 105 Mission rehearsal, 122, 129 Mode, 6, 10, 26, 84, 87, 101, 125 Monochromatic, 61, 88, 93 Motivation, 40 Mouth, 18, 19, 71 Moving map, 84 Multi-axial force environment, 48 Multi-axis, 47, 48 Multidimensional Aptitude Battery, See MAB Multi-function displays, 83, 84 Multi-sensor integration, 95 Muscle tremors, 23 Muscles, 36, 41, 53, 94 NATO, 121, 124, 128, 124 Nausea, 56 Navigation, 14, 84, 88, 89, 91, 95, 120, 128 Neck, 69, 74, 77, 94 injuries, 41, 48, 69, 70, 94, 108 pain, 41, 69 positioning strategies, 41 Netherlands air Force, 51 Network-centric, 95 Neural pathways, 53 Neuropsychological, 40, 117 Newton, 33 Night, 22, 52, 54, 58, 59, 61, 63, 67, 69, 70, 88, 92, 93, 95, 106, 123, 129 approach, 58 flying, 53, 92 ,93 operations, 52, 54, 61, 92, 129 Night vision goggles, See NVG Nitrogen, 17, 29, 30, 42

Noise attenuation, 67 Nomex, 66, 67, 72, 73, 74 Non-Cooperative Target Recognition, 87 Normobaric, 127 Nose, 8, 9, 16, 18, 19, 71, 84, 90, 92, 113 authority, 16 pointing, 8, 16 Nuclear weapons, 76 NVG, 61, 63, 67, 69, 70, 92–95, 106, 123, 129 Nystagmus, 56 OBOGS, 26, 29, 76 Off-boresight, 4, 6 Officer, 31, 63, 116, 117, 119, 120 Opening shock, 103, 109 Operating envelope, 16 Operational Conversion Unit, 121 Orientation, 36, 51, 52, 53, 54, 58, 59, 60, 61, 62, 92, 95 Otoliths, 52, 53, 54 Outlet valve, 72 Overbank, 57 Overheating, 74, 75 Oxygen, 15, 17–29, 31, 37, 39–42, 46, 48, 65, 67, 70, 71, 72, 76, 85, 100, 102, 109, 125, 126, 127 mask, See Mask Oxyhaemoglobin, 42 Pain, 18, 19, 29, 30, 41, 42, 68, 74, 111 Parachute, 68, 70, 78, 98, 100, 101, 102, 103, 105, 106, 109, 110, 112, 113 landing, 68, 109 risers, 109 Partial pressures, 17, 27 PBG, 46, 70, 73 PC-9, 120, 124 PCSM, 117 Perception, 39, 49, 50, 53, 60, 81, 82, 93, 94, 109, 117, 123 Performance envelope, 16, 17, 99, 104, 108 limitations, 16, 81, 89, 102, 115, 122 Perfusion, 41, 42, 43, 46 Peripheral vision, 37, 52 Personal equipment connector, 30 Personal radio transceiver, 74

Index Personal survival pack, 74 Personality, 117 Personality testing, 117 Personality traits, 117 Petechiae, 42 PFD, 89 Photoreceptor, 94 Physiological monitoring, 128 Physiotherapy, 111 Pilot Candidate Selection Method, 117 Pilot-in-the-loop, 62 Pincer movement, 12 Pitch, 8, 15, 16, 54, 84, 89, 128 Pitch-up illusion, 54 Pitch rate, 16 Plane of rotation, 56, 57 Pneumomediastinum, 18 Pneumothorax, 18 Polycarbonate, 67 Polystyrene, 67 Poor visual cues, 56 Positive pressure, 29, 42, 46, 71, 72, 73, 74 breathing, 46, 70, 73, 125, 126 Post-stall, 16, 47 Posture, 53, 102, 103, 106, 108, 122, 124 Precision-guided munitions, 13, 15 Pre-flight planning, 62, 83, 105 Premature ventricular, 42 Pressure differential, 18, 31 receptors, 53 schedule, 46 suit, 25, 31 Pressurised air, 26, 73 Primary flight display, 89 Proprioceptive system, 51, 52, 53, 61 Propulsion, 4, 6, 99, 112 Proteinuria, 42 Psychomotor, 22, 23, 117 Pursuit lag, 9 lead, 9 pure, 9 Pursuit curve, 9 RAAF, 21, 22, 28, 31, 37, 38, 41, 92, 103, 107, 118, 119, 120, 121, 127

155

Radar, 2, 3, 4, 6, 7, 11–14, 31, 84, 86–90, 92, 96, 112 signature, 89 Radar warning, 87 receiver, 7, 87, 89 Radiation, 6, 15, 76, 87, 88 Radio, 31, 37, 74, 84, 87, 89, 100, 102, 110, 126 RAF, 40, 51, 71, 73, 98, 103, 104, 107, 120, 121, 123, 127 RAF Centre of Aviation Medicine, 123 Rafale, 3, 73, 88, 96 Raft, 75, 100, 103, 109, 110 Range finders, 6 Rapid decompression, 27, 126, 127 Reasoning, 75 Reflected edge seal, 71 Refresher training, 61, 123 Refuelling, 12 Regulations, 21, 124 Regulator, 21, 28, 29, 30, 71 Relative incapacitation period, 39, 43 Renal, 42 Rescue, 110, 111 Respiration, 22 Respiratory, 18, 23, 30, 41, 42, 76 distress, 18 Restraint system, 100, 102 Restraints, 102 Retina, 22, 37 Rocket, 6, 13, 15, 99, 100, 101, 102, 112 motor, 13, 99, 100, 101, 102, 112 pack, 102 Roll rate, 48 Rotational accelerations, 69 Royal Air Force, See RAF Royal Aircraft Establishment, 98 Royal Australian Air Force, See RAAF Royal Danish Air Force, 69 Royal Navy, 98 Rubber, 19, 71, 76 Runway, 58, 59, 125, 126 Runway shape and slope illusions, 59 SAAB, 98 Safety-critical information, 82 Satellite, 14, 15 Scan, 87, 93

156

Flying Fast Jets

Scissors flat, 10 rolling, 10 SEAD, 14 Seat pan, 77, 102, 108 Seat pins, 101 Seat-back, 100, 103, 108 Seeker, 4, 5, 92 Selection, 26, 78, 84, 95, 96, 115, 116, 117, 118, 119, 121 Self-confidence, 116 Semi-circular canals, 52, 53, 55, 56, 57 Sensor, 1, 3, 7, 12, 15, 16, 29, 53, 69, 70, 81, 82, 83, 84, 86, 87, 88, 91, 92, 95, 96, 124 and display systems, 81 fusion, 3, 95, 96 suite, 86 systems, 7, 16, 70, 81, 82, 83, 84, 86, 87 Sensory integration, 53 Shadows, 57, 58, 129 Shortness of breath, 23, 30, 42 Sighting and display systems, 15, 48, 67, 69, 70, 94, 106, 116 Signal processing, 6, 88, 92 Simulation, 121, 128 Simulator, 62, 79, 121, 122, 124 Sinuses, 18, 19, 27 Sitting height, 77, 78 Situational awareness, 7, 10, 15, 38, 49, 60, 67, 69, 81–84, 86, 89–96, 116 definition, 81 Slant range, 15 Sleep, 40 Sloping cloud banks, 55 horizon, 51 Smoking, 24 Somatogravic illusion, 54 Somatogyral illusion, 56 Spatial disorientation, 16, 48–56, 58–62, 65, 91, 92, 94, 95, 122, 123, 124, 125 definition, 49 training, 124 Spinal cord, 107

fracture, 107 injuries, 103 Stability criteria, 16, 47 Stall, 8, 9, 54 Stealth, 2, 3, 16, 112 Strobe, 110 Su-25, 13 Su-27, 88 Su-30, 3 Su-35, 3 Super-agile, 3, 5, 16, 47, 48 Supercruise, 3 Supersonic, 2, 3, 68, 108, 109, 112, 120 Support close air, 14 Suppression of enemy air defences, See SEAD Surface-to-air, 14, 16 Surface-to-air missiles, 105 Survival, 8, 65, 74, 75, 86, 97, 100, 103, 104, 105, 109, 110, 123, 126, 127 rate, 105 time, 75 training, 110, 119 vest, 74 Sweating, 74 Sweden, 97, 98 Swedish Air Force, 73, 98 Symbology, 88, 92, 95 Sympathetic drive, 42 Synthetic, 54, 94, 95 T1, 120 T-38, 28, 120, 121 T-6, 120, 121, 124 Tactical situation sensors, 86 advantage, 9, 82 intercept, 48 Situation Awareness System, 62 Take-off, 54, 55, 58, 78 Target acquisition, 6, 87, 89 cueing, 87 Designator Controller, 84 Task fixation, 23 saturation, 51, 58, 61, 95

Index Teeth, 18 Tendons, 53 Terrain, 15, 47, 49, 57, 58, 59, 60, 83, 86, 88, 93, 106, 109, 110, 112, 122, 129 Awareness Warning System, 86 board, 129 Thermal burden, 75 energy, 31, 88 loading, 65 protection, 66, 75 Thermoplastic, 67, 70 Thoracolumbar, 107 Threat, 7, 12, 14, 20, 76, 87, 89, 91, 92, 95, 96, 111 Throttle, 26, 84, 85 Thrust, 6, 8, 16, 47, 99, 101, 112, 113 vectoring, 16, 47, 99, 112 Time of useful consciousness, 25 Tolerance human, 6, 15, 16, 24, 37, 43, 44, 46, 48, 72, 75, 128, 129 Tornado, 102, 121, 127 Touchscreen, 84 Track while scan, 87 Trajectory, 4, 13, 15, 57, 89, 90, 106, 112 Transverse axis, 35 Trapped gas, 18 Trigger, 44, 84, 93, 102 Tucano, 120 Tumbling, 56, 57, 109 Tunnel-vision, 22 Turn radius, 16, 34 UFC, 84, 85 Ultra-violet, 67 Unconsciousness, 23, 27, 37, 39, 40, 45, 126 Underbank, 57 United States, 48, 68, 97, 98, 120 United States Air Force, See USAF Unreality, 58 Unusual attitude, 50, 62, 95 Up-Front Controller, See UFC US Navy, 21, 38, 45, 50, 55, 58, 72, 73, 98, 120, 121, 127

157

USAF, 3, 21, 38, 40, 41, 47, 49, 50, 51, 55, 61, 70, 72, 73, 82, 98, 115, 117, 118, 120, 121 Valsalva manoeuvre, 19 Vascular tone, 44 Vectored thrust, See Thrust vectoring Velocity vector, 8, 48, 89, 90 Venous return, 45 Ventilation, 41, 42 Ventile, 74 Vertebral, 9, 106, 107, 108, 110, 111, 112 bodies, 107, 111 compression, 106, 112 fracture, 107, 108, 110, 111 Vertigo alternobaric, 19 Vestibular, 51, 52, 53, 56, 57, 61, 95, 124 Vigilance, 75 Visibility, 14, 54, 63, 78 Vision, 22, 23, 37, 52, 61, 63, 67, 69, 70, 88, 91, 92, 93, 94, 95, 106, 122, 123, 129 Visor, 67, 69, 91, 92, 103 Visual acuity, 22, 93 clutter, 61, 91 cues, 52, 53, 54, 56, 58, 61, 82, 91, 92 field, 37, 56 illusion, 52, 63 impairment, 36 system, 37, 52, 128 warning, 37, 44 Warhead, 4, 6, 13 Warning receivers, 7, 87 system, 88 tones, 86 Warnings, 7, 26, 27, 86 Water, 110 immersion, 74, 75, 78 Weapon employment zone, See WEZ Weapons cueing, 67, 88, 122 of mass destruction, 76 sighting systems, 84 Systems Officer, See WSO

158

Flying Fast Jets

Weather bad, 52, 53, 54, 61, 62, 88, 92 Weight, 22, 36, 41, 48, 65, 67, 68, 69, 73, 77, 94, 117 WEZ, 4 Windblast, 67, 68, 71, 77, 97, 101, 102, 108, 109, 112 Workload, 29, 46, 50, 53, 58, 60, 78, 87, 89, 91, 92, 94, 95, 96, 118

WSO, 63 Xenon, 17 Yo-yo, 9, 10 Z axis, 36 Zero-zero, 101 Zvezda, 99, 101