Professional airline Pilots' Stress, Sleep Problems, Fatigue and Mental Health in Terms of Depression, Anxiety, Common Mental Disorders, and Wellbeing in Times of Economic Pressure and Covid19 E-Book

Marion Venus

• Herausgeber: tredition
• Kategorie: Fachliteratur
• Serie: Aviation Psychology & Human Factors
• Sprache: Englisch
• Veröffentlichungsjahr: 2022

Seitenzahl: 534

Beschreibung

The aim of this dissertation was to examine two so far separately considered complex constructs, fatigue and mental health, concerning a target group that has to cope with high stress, extraordinary workload, high risks and responsibility: professional pilots. The complexity of the psychophysiological construct fatigue should be highlighted. Potential correlations and interactions of stress with fatigue, sleep problems, mental health and well-being should be investigated. It seemed necessary to consider pilot fatigue not only in the context of sleep medicine, but also in context with the Theory of Allostasis, clinical, work psychology and burnout research. Studies one and two investigated, if our com-prehensive dataset of 406 pilots would support the Theory of Allostasis. Complex anal-yses confirmed that acute and chronic work-related and psychosocial stress were signifi-cantly associated with more psychophysiological wear and tear processes like high fa-tigue, sleep problems, impaired well-being and more symptoms of depression, anxiety, and CMD. The third study was a Qualitative Content Analysis of pilots' experiences, which perfectly confirmed the quantitative results of all five studies and the Theory of Allostasis. Studies 4, 5 and 6 compared groups of pilots. Australian pilots were slightly more affected than EASA-based pilots. Short-haul pilots of low-cost-carriers were most affected, reporting excessive fatigue, the most sleep problems, the most symptoms of depression, anxiety and CMD, and the most impaired well-being. These first six explora-tory studies have not received any funding but have identified important new research topics. These complex, new results should be the basis of future research regarding pi-lots' fatigue, health and flight safety in general. Das Ziel dieser Dissertation war es, zwei bisher getrennt betrachtete komplexe Konstrukte, Müdigkeit und psychische Gesundheit, in Bezug auf eine Zielgruppe zu untersuchen, die mit hohem Stress, außergewöhnlicher Arbeitsbelastung, hohen Risiken und Verantwortung fertig werden muss: Berufspiloten. Die Komplexität des psychophysiologischen Konstrukts Fatigue soll hervorgehoben werden. Mögliche Korrelationen und Wechselwirkungen von Stress mit Müdigkeit, Schlafproblemen, psychischer Gesundheit und Wohlbefinden sollten untersucht werden. Es schien notwendig, Pilotenmüdigkeit nicht nur im Kontext der Schlafmedizin, sondern auch im Zusammenhang mit der Theorie der Allostase, der klinischen, arbeitspsychologischen und Burnout-Forschung zu betrachten. Die Studien eins und zwei untersuchten, ob unser umfassender Datensatz von 406 Piloten die Theorie der Allostase stützen würde. Komplexe Analysen bestätigten, dass akuter und chronischer arbeitsbedingter und psychosozialer Stress signifikant mit mehr psychophysiologischen Verschleißprozessen wie hoher Erschöpfung, Schlafproblemen, beeinträchtigtem Wohlbefinden und mehr Symptomen von Depressionen, Angstzuständen und CMD assoziiert waren . Die dritte Studie war eine qualitative Inhaltsanalyse der Erfahrungen von Piloten, die die quantitativen Ergebnisse aller fünf Studien und die Theorie der Allostase perfekt bestätigte. Die Studien 4, 5 und 6 verglichen Gruppen von Piloten. Australische Piloten waren etwas stärker betroffen als EASA-basierte Piloten. Kurzstreckenpiloten von Billigfliegern waren am stärksten betroffen und berichteten von übermäßiger Müdigkeit, den meisten Schlafproblemen, den meisten Symptomen von Depressionen, Angstzuständen und CMD sowie dem am stärksten beeinträchtigten Wohlbefinden. Diese ersten sechs explorativen Studien wurden nicht finanziert, haben aber wichtige neue Forschungsthemen identifiziert. Diese komplexen, neuen Ergebnisse sollten die Grundlage für zukünftige Forschungen zu Ermüdung, Gesundheit und Flugsicherheit von Piloten im Allgemeinen sein.

Leseprobe

PILOTS’ STRESS, SLEEP, FATIGUE & MENTAL HEALTH

MARION VENUS

Correlations and Interactions of Professional Pilots’

Duty Rosters,

Work-related and Psychosocial Stress, Sleep Problems,

Fatigue,

Mental Health and Well-being

New insights into known threats to flight safety

Inauguraldissertation

der philosophisch-humanwissenschaftlichen Fakultät der Universität Bern

zur Erlangung der Doktorwürde

vorgelegt von

BA Mag. rer. nat. Marion Venus

Matrikelnr.: 17-135-153

Bern, August 2022

© 2023 Dr. Marion Venus

ISBN

Softcover:

978-3-347-72205-7

ISBN

Hardcover:

978-3-347-72206-4

ISBN E-Book:

978-3-347-72212-5

Printing and distribution on behalf of the author: tredition GmbH, An der Strusbek 10, 22926 Ahrensburg, Germany

The work including its parts is protected by copyright. The author is responsible for the content. Any use is not permitted without your consent. The publication and distribution are carried out on behalf of the author, who can be reached at: tredition GmbH, "Imprint Service" department, An der Strusbek 10, 22926 Ahrensburg, Germany.

From the Faculty of Philosophy and Human Sciences at the University of Bern at the request of Prof. Dr. Martin Große Holtforth (main reviewer) and Prof. Dr. Achim Elfering (second reviewer) accepted.

Berne, November 22, 2022

The dean: Prof. Dr. Stefan Troche

Ich widme meine gesamte Arbeit meiner innig geliebten Omi, Maria Venus In ewiger Liebe und Dankbarkeit

Preface

Over 100 years ago, flying was an adventure with many fatalities. Later, flying became an absolute luxury. Pilots cultivated an amazing lifestyle, enjoyed high reputation, very pleasant working hours, lots of free time, long stays in fantastic holiday destinations and high income. That changed quickly when politicians and regulators liberalized aviation, and alongside the luxurious, expensive flag or network carriers (NWC, e.g., British Airways, Qantas, Lufthansa), low-cost airlines (LCC) launched a revolutionary new business model with new management strategies (Alamdari & Fagan, 2005; Hunter, 2006; ITF, 2002; Pate & Beaumont, 2006; Štimac et al., 2012; Vidović et al., 2013). LCC opened new markets, offered cheap airline tickets and made aviation accessible not only to the rich, but also to ordinary people. Commercial air operators had to minimize their costs, e.g., hire as few pilots as possible and keep them on flight duty for as long as possible. Also, planes must fly as much as possible, to earn money and maximize productivity, to remain competitive. Pilots’ working conditions eroded, and aircrews (i.e., pilots and cabin crew members) had to work more and more hours per month and per year, based on lower salaries due to new work contracts after airline mergers (i.e., merger of Swissair and Crossair, then Lufthansa bought Swiss and Austrian Airlines, with the option for pilots to quit or accept a new contract with lower and lower salaries). LCC started with atypical, precarious work contracts, based on bogus self-employment or employment via an intermediary manning agency (Brannigan et al., 2019; Reader et al., 2016).

After the Germanwings crash, airline management, regulators, passengers and aircrews (incl. pilots) were shocked: Who is the other person on the flightdeck? Can I trust him/her? What happens when I go to the bathroom or rest on the bunk bed? At the same time, every pilot feared long time grounding and finally losing his/her medical class 1 certificate, if their responsible aeromedical examiner (AME) suspected or diagnosed any mental impairment. A German pilot representative told me, “The [AME’s] gut feeling is enough. If the AME thinks a pilot might hide some life event or mental health issue: Instead of diagnostics, just a healthy mistrust or a gut feeling that the pilot is almost certainly hiding something, is enough for aeromedical examiners to suspend the medical certification. Often for six months, and nobody knew, why’. Attending continuing peer support and CISM trainings at the Mayday Foundation, I heard many background stories regarding the copilot, who intentionally crashed the Germanwings Airbus. When I presented at several scientific meetings of aerospace physicians and aeromedical examiners, I also attended the whole conference and social events. There I had many opportunities to gain insights into AME’s mindset, and the reasons for their distrust in pilots. Professional ethics implies, that AMEs, who call their customers (pilots) “criminal liars and cheaters” should quit and work with other clients or patient groups. The same for aviation psychologists, which are usually only in charge of pilot selection. Those, who I met at congresses in Sydney or Bangkok uttered the same ‘compliment’ about their customers, professional pilots of airlines in Australia, the USA and the Middle East. One of them works for a big company, which selects pilots for Australian, Middle Eastern and US carriers. He said something to the effect, ‘It has become popular for pilots to complain that they are suffering from fatigue and sleep problems, while they are simply hiding a pathological anxiety disorder . Pilots are criminal liars and cheaters.’ Quite unethical to talk like that about his clients or patients. Of course, just his opinion, not based on any facts or published scientific evidence. He had heard my presentation, and this was what he wanted to tell me. I was appalled but kept this unethical and – in my professional opinion – simply wrong conclusion in mind, to see if I could prove him wrong, based on my data.

I was deeply interested in the present working-conditions of professional pilots, who fly for different types of carriers (airlines or NWC, LCC, cargo and charter operators), and different types of flight operations (short-haul, medium, and long-haul). I spent hundreds of hours listening to pilots describing their own experiences, analyzing fatigue and mental health issues associated with short-haul and long-haul flight ops, based on their psychological background or long years of self-experience in both areas. I also heard how they managed emergencies and situations like engine failure combined with a collapse of all electronic systems on a skill-check-flight, or stories of severe fatigue in the cockpit, where one or both pilots had fallen asleep without prior coordination.

The Germanwings crash in 2015 (BEA, 2016) was a wakeup call for the aviation system, air operators as well as regulators and passengers. Suddenly we had to realize that pilots were human beings, not just superior computers with brains, operators of avionics and flight systems, the eyes, ears, brain, arms, feet etc. of huge passenger jets. Right after the Germanwings crash, I attended my first aviation safety conference of the European Aviation Safety Agency (EASA). When EASA started to develop new measures to better monitor pilots’ mental health, I could watch and contribute as an expert for clinical and aviation psychology, health and safety management, and being a pilot myself. As pilot I met many senior commanders and pilot representatives. They explained my how aviation has been changing in the last 20 to 30 years. Low-Cost Carriers like e.g., Ryanair usually do not even offer employment contracts to their pilots, but pay pilots per flight hour, not per month. Great from an economic point of view because the air operator does not have to pay pilots when they are ill, on vacation or absent due to extreme fatigue or exhaustion. Not so great for new pilots who start their careers with high loans for self-financed pilot training (costs from 100’000 to 130’000 €). New pilots must fly as much as possible, so that they can cover their living expenses, and survive winter, with only few flight hours, while having to pay back their loan installments, while no unemployment insurance pays. From November until March – beyond peak flight season – pilots can rest and recover a bit, with minimum regular income, and no performance-based additional income due to almost no flight hours off season. Under enormous economic pressure, more duty and flight hours and shorter minimum rests, many psychosocial stressors from low income to high job insecurity, high fatigue may not be pilots’ only problem, as more and more pilots reported high burnout levels (Demerouti et al., 2019; Fanjoy et al., 2010).

I would like to thank my dear friends who have supported my research gratuitously in their meager free time, to name a few: Commander MSc HF Pete Wilson, Commander Michael Gruber BA BSc MA, MSc, PhD Cand. Commander Chris Smith (Senior Lecturer University of Southern Queensland), Prof. Dr. Samira Bourgeoise-Bougrine, Senior First Officer Michèle Finger, Commander Bastien Kynast (TRI, TRE, CRM), Commander Daya Rishy-Maharaj (Cargo), and Commander Dirk Polloczek (former President of the European Pilots Association), Lachlan Gray (AFAP; flight safety).

My special thanks go to my PhD supervisor Prof. Dr. Martin grosse Holtforth, who was immediately interested in my complex and complicated, multidimensional PhD topic. He patiently guided me through my rough and hot topic and results, which introduced him to the dire, ugly aspects of modern aviation. Two papers won awards in 2021, 1st Runner Up of the “Young Investigator’s Award“ YIA of the Aerospace Medical Association (AsMA) for “How professional pilots perceive interactions of working conditions, rosters, stress, sleep problems, fatigue and mental health. A qualitative content analysis”, and the 2nd place of the Aerospace Medical Association (ASMA) Fellows Scholarship for my presentation at the AsMA meeting 2021 and the publication “Short and Long-Haul Pilots’ Rosters, Stress, Sleep Problems, Fatigue, Mental Health and Wellbeing”

Content

1 Introduction

1.1 A short History of Pilots’ Fatigue and Mental Health Research

1.2 Pilot Mental Health or the Pilots’ Human Side

1.3 A Short History of Fatigue Research

1.4 What if FTL and FRM have failed …?

1.4.1 Research Questions of Traditional Fatigue Studies

1.4.2 Potential Modification of Behavior and the ‘Hawthorne’, or ‘Rosenthal Effect’

1.4.3 Representativity of the Investigated Pilot Samples

1.4.4 Fatigue and Sleepiness Self-Reports

1.4.5 Measuring the Symptom Sleepiness vs. the Complex Construct of Fatigue

1.4.6 The Use of Actigraphy to Measure Sleep

1.4.7 Biomathematical Models (BMM)

1.4.8 Psychomotor Vigilance Test (PVT) to Measure Fatigue Related Performance Decrements

1.4.9 Flight Time Limitations and Working Time Arrangements in General

1.4.10 Conclusions

1.5 The Relevance of Pilots' Physical and Mental Health for Flight Safety and Regulatory Authorities

1.6 A Pilot’s Life – Decades ago and Today

1.6.1 Examples of Work-related Stressors for Pilots

1.6.2 Examples of Psychosocial Stressors Especially for Pilots

2 Summary of the Submitted Articles

2.1 How Duty Rosters and Stress Relate to Sleep Problems and Fatigue of International Pilots.

2.1.1 Aims and Questions

2.1.2 Procedure

2.1.3 Material

2.1.4 Statistical Analyses

2.1.5 Participants

2.1.6 Results

2.2 Interactions of International Pilots’ Stress, Fatigue, Symptoms of Depression, Anxiety, Common Mental Disorders and Wellbeing

2.2.1 Aims and Questions

2.2.2 Participants

2.2.3 Procredure

2.2.4 Material

2.2.5 Statistical Analyses

2.2.6 Results

2.3 How Professional Pilots Perceive Interactions of Working Conditions, Rosters, Stress, Sleep Problems, Fatigue and Mental Health. A Qualitative Content Analysis (QCA)

2.3.1 Aims and Questions

2.3.2 Participants

2.3.3 Procedure

2.3.4 Results

2.4 Short and Long-Haul Pilots’ Rosters, Stress, Sleep Problems, Fatigue, Mental Health and Wellbeing

2.4.1 Aims and Questions

2.4.2 Participants

2.4.3 Procedure and Material

2.4.4 Statistical Analyses

2.4.5 Results

2.5 Australian and EASA-based pilots ’ duty schedules, stress, sleep difficulties, fatigue, wellbeing, symptoms of depression and anxiety 52

2.5.1 Participants

2.5.2 Procedure and Material

2.5.3 Statistical Analyses

2.5.4 Results

2.6 Comparison of Schedules, Stress, Sleep Problems, Fatigue, Mental Health and Well-being of Low Cost and Network Carrier Pilots

2.6.1 Aims and Questions

2.6.2 Participants

2.6.3 Procedure and Material

2.6.4 Statistical Analyses

2.6.5 Results

3 Discussion

3.1 General Discussion

3.2 Interactions of International Pilots' Rosters, Stress, Sleep problems, Fatigue, Symptoms of Depression, Anxiety, Common Mental Disorders and Wellbeing (Studies 1 and 2)

3.3 How professional pilots perceive interactions of working conditions, rosters, stress, sleep problems, fatigue and mental health. A qualitative content analysis

3.4 Short and Long-Haul Pilots’ Rosters, Stress, Sleep Problems, Fatigue, Mental Health and Wellbeing

3.5 Australian and EASA-based pilots ’ duty schedules, stress, sleep difficulties, fatigue, wellbeing, symptoms of depression and anxiety

3.6 Comparison of Schedules, Stress, Sleep Problems, Fatigue, Mental Health and Well-being of Low Cost and Network Carrier Pilots

3.7 Implications for Pilots Fatigue and Mental Health

3.8 Limitations

3.9 Strengths

3.10 Research Implications and Conclusions

4 How Duty Rosters and Stress Relate to Sleep Problems and Fatigue of International Pilots

4.1 Introduction

4.1.1 Flight Time Limitations and Fatigue Prevention

4.1.2 Homeostasis, Stress, Allostasis and Allostatic Load

4.2 Problem and Purpose

4.2.1 Biomathematical Models (BMM), Fatigue Risk Management (FRM) & Resulting Rosters

4.2.2 Fatigue & Safety

4.2.3 Differentiation Between Sleepiness and Fatigue

4.2.4 Stress, Sleep & Fatigue

4.3 Method

4.3.1 Design and Procedure

4.3.2 Subjects

4.3.3 Description of the Online Survey

4.3.4 Statistical Evaluation

4.4 Results

4.4.1 Roster Data

4.4.2 Fatigue Risks Associated with Flight Duties, Micro-Sleep in the Cockpit and Concerns regarding FTL

4.4.3 Pilots’ Fatigue Levels and Sleep Problems

4.4.4 Intercorrelations of Stress, Fatigue and Sleep Problems

4.4.5 Predictors of Sleep Problems

4.4.6 Predictors of Fatigue

4.5 Discussion

4.5.1 Fatigue and Sleep Problems

4.5.2 Comparison of our Results with Previous Research

4.5.3 Stress, Allostatic Load, Sleep Problems and Fatigue

4.5.4 Fatigue and Micro-Sleep in the Cockpit

4.5.5 Limitations

4.5.6 Strengths

4.5.7 Research Implications

4.5.8 Conclusions

5 Interactions of International Pilots' Stress, Fatigue, Symptoms of Depression, Anxiety, Common Mental Disorders and Wellbeing

5.1 Introduction

5.1.1 Workload, Stress, Fatigue, Mental Health and Wellbeing

5.1.2 Homeostasis, Stress, Allostasis and Allostatic Load

5.1.3 Stress and Sleep

5.1.4 Flight Time Limitations and Economic Pressure

5.1.5 Research Questions

5.2 Method

5.2.1 Design and Procedure

5.2.2 Procedure

5.2.3 Subjects

5.2.4 Statistical Analysis

5.3 Results

5.3.1 Pilots’ Mental Health and Wellbeing

5.3.2 Intercorrelations between Stress, Sleep, Fatigue, Mental Health and Wellbeing

5.4 Discussion and Conclusions

5.4.1 Pilots’ Rosters and Fatigue

5.4.2 Pilots’ Sleep Problems

5.4.3 Pilots’ Mental Health and Wellbeing

5.4.4 Differentiation of Sleepiness and Fatigue, Fatigue and Mental Health

5.4.5 Stress, Sleep and Burnout

5.4.6 Research Implications

5.4.7 Limitations

5.4.8 Strengths

5.4.9 Conclusions

6 How Professional Pilots Perceive Interactions of Working Conditions, Rosters, Stress, Sleep Problems, Fatigue and Mental Health. A Qualitative Content Analysis

6.1 Introduction

6.1.1 High Fatigue among Pilots, Stress and Safety relevant Fatigue Consequences

6.1.2 Germanwings Crash & Pilot Mental Health

6.1.3 ‘Pilot Pushing’ & Burnout

6.1.4 Research Questions

6.2 Method

6.2.1 Procedure

6.2.2 Participants

6.2.3 Description of the Cross-Sectional Online Survey

6.2.4 Qualitative Content Analysis (QCA) by Mayring (2014)

6.2.5 Inter-Coder and Intra-Coder Reliability of QCA

6.3 Results

6.3.1 Summary of the Quantitative Results

6.3.2 Frequency Analysis

6.3.3 Content of the most relevant Codings

6.3.4 QCA: Comparison of Australian vs. EASA-based Pilots

6.4 Discussion

6.4.1 Limitations

6.4.2 Strengths: Advantages of QCA

6.4.3 Research Implications

6.4.4 Conclusions

7 Short and Long-Haul Pilots’ Rosters, Stress, Sleep Problems, Fatigue, Mental Health and Wellbeing

7.1 Introduction

7.2 Method

7.2.1 Procedure

7.2.2 Subjects

7.2.3 Material: Cross Sectional Online Survey and Used Questionnaires

7.2.4 Statistical Analyses

7.3 Results

7.4 Discussion

8 Australian and EASA Based Pilots’ Duty Schedules, Stress, Sleep Difficulties, Fatigue, Wellbeing, Symptoms of Depression and Anxiety

8.1 Introduction

8.1.1 Definitions of Sleepiness and Fatigue

8.1.2 Stress, Sleep and Health

8.1.3 High Fatigue and Micro-sleep despite Fatigue Risk Management and FTL

8.2 Research Questions

8.2.1 Fatigue, Fatigue Related Performance Decrements and Flight Safety

8.2.2 Stress, Sleep, Fatigue and Mental Health

8.3 Method

8.3.1 Procedure

8.3.2 Participants

8.3.3 Description of the Cross-Sectional Online Survey

8.3.4 Statistical Analyses

8.4 Findings

8.4.1 Descriptive Results

8.4.2 Hypothesis Testing

8.5 Discussion

8.5.1 Pilots’ Mental Health & Wellbeing

8.5.2 Fatigue Risks, FTL and Flight Safety

8.5.3 Limitations

8.5.4 Strengths

8.5.5 Research Implications

8.5.6 Conclusions

9 Comparison of Schedules, Stress, Sleep Problems, Fatigue, Mental Health and Well-being of Low Cost and Network Carrier Pilots

9.1 Introduction

9.1.1 Problem

9.1.2 Definitions of Fatigue

9.1.3 Fatigue and Mental Health Issues Among Pilots

9.1.4 Accumulated Fatigue and Micro-Sleep in the Cockpit

9.1.5 Multiple Stressors for Aircrews

9.1.6 Research Questions and Hypotheses

9.2 Material and Method

9.2.1 Procedure

9.2.2 Participants

9.2.3 Material

9.2.4 Statistical Analysis

9.3 Results

9.4 Discussion

9.4.1 Limitations

9.4.2 Strengths

9.4.3 Conclusions

10 List of Figures

11 List of Tables

12 Supplemental Materials

12.1 Used Standardized Questionnaires

12.2 Supplemental Material Study 3

12.2.1 Coding Guidelines

12.2.2 Category System

12.3 Supplemental Material Study 5

12.4 Supplemental Material Study 6

13 References

14 Statement of Authorship

List of Abbreviations

FTL

Flight time limitations

FRM

FRM

BMM

Biomathematical Models

FDP

Flight duty period

EASA

European Aviation Safety Agency

ICAO

Civil Aviation Safety Authority

FAA

Federal Aviation Administration

CMD

Common mental disorders

ICAO

International Civil Aviation Organization

CMD

Common mental disorders

SOP

Standard Operational Procedures

PHQ8

Patient-Health-Questionnaire-8

GAD7

Generalized Anxiety Disorder-7

SRQ20

Self-Reporting-Questionnaire-20

PHQ-Stress

Patient-Health-Questionnaire-Stress

FSS

Fatigue Severity Scale

JSS

Jenkins Sleep Scale

WHO5

World Health Organization -5 Well-being Index

Flight ops

Flight operations

Abstract

The aim of this dissertation was to examine two so far separately considered complex constructs, fatigue and mental health, concerning a target group that has to cope with high stress, extraordinary workload, high risks and responsibility: professional pilots. The complexity of the psychophysiological construct fatigue should be highlighted. Potential correlations and interactions of stress with fatigue, sleep problems, mental health and well-being should be investigated. It seemed necessary to consider pilot fatigue not only in the context of sleep medicine, but also in context with the Theory of Allostasis, clinical, work psychology and burnout research. Studies one and two investigated, if our comprehensive dataset of 406 pilots would support the Theory of Allostasis. Complex analyses confirmed that acute and chronic work-related and psychosocial stress were significantly associated with more psychophysiological wear and tear processes like high fatigue, sleep problems, impaired well-being and more symptoms of depression, anxiety, and CMD. The third study was a Qualitative Content Analysis of pilots’ experiences, which perfectly confirmed the quantitative results of all five studies and the Theory of Allostasis. Studies 4, 5 and 6 compared groups of pilots. Australian pilots were slightly more affected than EASA-based pilots. Short-haul pilots of low-cost-carriers were most affected, reporting excessive fatigue, the most sleep problems, the most symptoms of depression, anxiety and CMD, and the most impaired well-being. These first six exploratory studies have not received any funding but have identified important new research topics. These complex, new results should be the basis of future research regarding pilots’ fatigue, health and flight safety in general.

1 Introduction

Airline pilots spend most of their duty and flight hours in their ‘front office’ several kilometers above the ground, in a hostile environment with outside temperatures of about minus 55 Degrees Celsius and not enough oxygen to stay conscious for more than a minute in case of rapid decompression. On the flight deck, pilots operate complex, cutting edge, interacting automated systems in the high-risk high-reliability system aviation. The technical aspects of flight safety have steadily improved over the last decades, although technical failures still lead to fatal crashes, e.g., the malfunction of the MCAS system of the newly released Boeing 737-Max of Lion Air (KNKT, 2019) and Ethiopian Airlines (AIB et al., 2020), or iced pitot tubes (BEA, 2012). Nevertheless, a new threat to flight safety has been discovered. Increasing duty and flight hours and competitive, but still legal rosters have resulted in high levels of pilot fatigue. High levels of on-duty sleepiness and fatigue can affect pilots’ performance and decision-making, and threaten flight safety (Bandeira et al., 2018; Bendak & Rashid, 2020; Bourgeois-Bougrine, 2020; Goode, 2003; Hartzler, 2014). This PhD refers to professional pilots, in contrast to private or glider pilots, and also differs distinctly between sleepiness and fatigue (Shahid et al., 2010).

Fatigue related, unintentional microsleep events1 on the flight deck represent a significant threat to flight safety, due to loss of safety essential situational awareness (Coombes et al., 2020; Kharoufah et al., 2018; Rosa et al., 2020). Although pilot unions have been warning about rising levels of pilot fatigue for many years, regulators have not reacted. According to recent research (Aljurf et al., 2018; Coombes et al., 2020; Williamson & Friswell, 2017), microsleep events in the cockpit are fairly frequent, although flight time limitations (FTL, examples Table 1) and fatigue risk management (FRM) should prevent microsleep and excessive fatigue.

In addition to higher propensity to fall asleep, fatigued pilots tend to make more errors of omission and commission, their judgement, decision making ability and short term memory degrades, their mood deteriorates, pilots’ irritability is higher, and pilots’ flying skills degrade (Coombes et al., 2020; Hartzler, 2014). Microsleep events in the cockpit are reported by 45% of the pilots (Aljurf et al., 2018; Williamson & Friswell, 2017). Per 1000 flight hours, pilots reported 7.3 cases of involuntary sleep of one pilot on the flight deck (Coombes et al., 2020), two thirds of the investigated pilots reported fatigue-related errors during active flight duty. These facts suggest that FTL and FRM (FRM) are less effective than expected (Bourgeois-Bougrine, 2020; Coombes et al., 2020; Demerouti et al., 2019; Efthymiou et al., 2021).

Table 1: Examples of basic flight time limitations (FTL) rules of the European Aviation Safety Agency (EASA), Civil Aviation Safety Authority (CASA) and the US Federal Aviation Administration (FAA). These FTL were in force during the time of data collection from June 2018 until March 2019 (Venus & grosse Holtforth, 2021a)Klicken oder tippen Sie hier, um Text einzugeben.

Flight Time Limitations in effect until March 2019

EASA FTL: ORO.FTL.210

CASA FTL 48.1

FAA Part 121

Max. duty hours

13 duty hours

14 duty hours

14 duty hours

Duty period or duty hours*/pilot (multi pilot operation)

Max. duty hours/month

190 duty hours

200 duty hours

Commander’s Discretion (Extension of max. duty hours)

max. 13 duty hours plus max. 2 duty hours

max. 14 duty hours plus max. 1 duty hour

max. 14 duty hours plus max. 2 duty hours

Augmented Crews§

depending on time of day

FDP > 9 to 13 duty hours

FDP > 8 to 14 duty hours

FDP > 9 to 14 duty hours

Flight hours†/pilot (multi pilot operation)

In any 28 consecutive days

100 flight hours

100 flight hours

100 flight hours

In any calendar year

900 flight hours

1000 flight hours

In any 12 consec. Months

1000 flight hours

1000 flight hours

Minimum rest‡

Before flight duty

10 hours (exceptions)

10 hours (exceptions)

10 hours

Note.

All definitions from EASA FTL (2014, pp.-22):

*) “Duty period [duty hours] means a period which starts when a crew member is required by an operator to report for or to commence a duty and ends when that person is free of all duties, including post-flight duty;”

§) “augmented flight crew means a flight crew which comprises more than the minimum number required to operate the aircraft, allowing each flight crew member to leave the assigned post, for the purpose of in-flight rest, and to be replaced by another appropriately qualified flight crew member;”

†) “Flight time [flight hours] means the time between an aircraft first moving from its parking place for the purpose of taking off until it comes to rest on the designated parking position and all engines or propellers are shut down;”

‡) “Rest period means a continuous, uninterrupted and defined period of time, following duty or prior to duty, during which a crew member is free of all duties, standby and reserve;”

1.1 A short History of Pilots’ Fatigue and Mental Health Research

In the 1980s, pilots reported on average 45.7±30 flight hours/month (M±SD) (Sloan & Cooper, 1986), while present flight time limitations (e.g., CASA FTL, 2013; EASA FTL, 2014) allow up to 100 flight hours and 1000 flight hours per year (examples Table 1, suppl. material). Severe fatigue contributed to several crashes or severe incidents like China Airlines 006 (NTSB, 1987), Korean Air 801 (NTSB, 2000), American Airlines 1420 (NTSB, 2001) and the TransAsia crashes (ASC, 2015, 2016), while fatigue and precarious working conditions contributed to the crash of Colgan Air 3407 (NTSB, 2010). These accidents or crashes caused 380 fatalities; 170 persons were injured. Pilot mental health has only come into media and public focus after the planned aircraft assisted suicide and mass murder crashes (Laukkala et al., 2018) such as the Germanwings crash in 2015 (BEA, 2016), while the previous LAM crash in 2013 (MWT, 2016) remained almost unnoticed, similar to the EgyptAir 990 crash (NTSB, 1999a), which was caused by a previously demoted pilot. The most recent crash of China Eastern in March 20222 is suspected to be the latest intentional aircraft assisted suicide crash of a fully functional, almost new Boeing 737-800. Mulder & de Rooy (2018) concluded, acute mental health problems and a series of negative life events played a substantial role in seventeen commercial aviation accidents and incidents with 576 fatalities.

So far, pilot fatigue and mental health were treated as separate issues. While pilot mental health has only become a relevant research topic in the recent years (Aljurf et al., 2018; Cahill et al., 2021; Cullen et al., 2020; Mulder & de Rooy, 2018; O’Hagan et al., 2016, 2017, 2019; Widyahening, 2007; AC. Wu et al., 2016), NASA started fatigue research in the 1990’s (Bourgeois-Bougrine et al., 2003; Caldwell, 2005; Graeber & Dinges, 1994; Petrie & Dawson, 1997; Petrilli et al., 2006; Powell et al., 2010; Roach, Petrilli, et al., 2012).

In the following section, the research topics pilot mental health and pilot fatigue are examined in more detail, possible weaknesses of the traditional research approach are pointed out.

1.2 Pilot Mental Health or the Pilots’ Human Side

Until the Germanwings crash, pilot mental health was not on the radar of most aviation psychologists or human factors specialists. Pilots were seen as extensions of cutting-edge technology in the cockpit, rational achievers recruited from the top two percent of the general population. Pilots have always been expected to perform at their best in every situation, from the middle of the night in a tropical thunderstorm to the wind shears on final approach at London City Airport. The intentional suicide-murder crashes mentioned above have produced a new research topic: Pilots’ mental health.

So far, only a few crashes have been caused by a pilot in the cockpit, killing everyone on board (BEA, 2016; MWT, 2016; NTSB, 1999a), the Western China accident report (crash in March 2022) is not available yet. In these cases, the commander or co-pilot had a known history of a) persistent suicidality, and/or b) recurrent major depression with or without schizophrenic symptoms, and/or c) was on antidepressant medication and/or d) had experienced several serious life events or family losses before he intentionally crashed a technically perfect passenger plane, killing all passengers and crew on board. Only then media and the public became aware, that pilots are humans, not advanced technical infrastructure on the flight deck. Pilots all over the world were shocked. A security measure after 9/11 – a securely locked cockpit-door to keep terrorists off the flight deck – cost the lives of 183 persons on board (or up to 315 fatalities including the Western China crash).

To prevent this type of fatal crash in the future, the European Aviation Safety Agency (EASA) made the following measures mandatory: Mental health assessment of pilots with the first and recurrent medical class 1 certification, pilot (peer) support, testing safety critical aviation staff for drugs and any psychoactive substances. Regulatory agencies treated aircrews’ mental health as an isolated issue for aeromedical examiners, leaving rampant fatigue issues to officers with economic background (e.g., at EASA) or other staff (e.g., CASA).

Pilots are selected according to their cognitive abilities, stable personality, their mental and physical health is screened, and pilots generally represent a healthy population (Sykes et al., 2012). So how would depressive disorders become an issue for pilots? Could fatigue play a role?

1.3 A Short History of Fatigue Research

In the good old days of aviation, there were no flight time limits. It was up to airlines, how they wanted to schedule their pilots. For example, after a long-haul flight from Europe to another continent, aircrews (i.e., pilots and cabin crews, navigators, flight technicians) spent several days or a week at the (holiday) destination, before they returned to their homebase. After low-cost carriers (LCC) revolutionized aviation around the world (Alamdari & Fagan, 2005; Hunter, 2006; ITF, 2002; Pate & Beaumont, 2006; Štimac et al., 2012; Vidović et al., 2013), competition between airlines started. Airline tickets became significantly cheaper, flying was no longer a luxury, and airlines began to economize wherever needed – the plan being to generate more revenue with fewer staff by using aircrews and big passenger jets as much as possible (Brannigan et al., 2019; Fanjoy et al., 2010).

The first EASA FTL were introduced in 2008. They should limit duty and flight hours and regulate sufficient rest times for pilots and cabin crews. The updated FTL (EASA FTL, 2014) were originally based on scientific evidence (Moebus, 2008), but they were immediately rejected by the aviation industry of EASA member states. The final version of the EASA FTL was allegedly dictated by the aviation industry (EASA FTL, 2014). According to the International Labor Organization (ILO, 2019a, 2019b), work time arrangements must be designed to maintain workers’ and employees’ occupational health and safety. But can they, if they were based on a ‘wish list’ of commercial air operators, not on scientific evidence? Pilots can lose up to 40% of their regular sleep time (Cabon et al., 2012; Coombes et al., 2020), due to legal but competitive rosters and FRM. Today, most rosters for aircrews are the output of scheduling software, based on biomathematical models (BMM, e.g., Dawson et al., 2017; Dorrian et al., 2012; Ingre et al., 2014). With BMM software, crew planners and air operators can decide whether to use their crews to the legal maximum or to protect the health and safety of their aircrews. BMM generally state that they prevent fatigue. So, why have studies found, and pilot unions complained about high levels of fatigue among pilots for years (Aljurf et al., 2018; Jackson & Earl, 2006; Reis et al., 2013, 2016b)? Could fatigue research, FTL and FRM have failed?

1.4 What if FTL and FRM have failed …?

It seems that all efforts of FTL, FRM (FRM) and fatigue studies have not been very successful in preventing high levels of fatigue among pilots. Samira Bourgeois-Bougrine (2020) discusses the “Illusion of aircrews' fatigue risk control”, Efthymiou et al. (2021) reported significant fatigue issues associated with FTL, FRM and resulting rosters. Pilots tend to underreport fatigue, not only mental health issues (Strand et al., 2022). Lee & Kim (2018) investigated factors which can affect fatigue, but ongoing austerity measures have prevented the implementation of these factors to prevent fatigue. Some pilot selection psychologists and fatigue researchers have attributed the consistently reported high levels of pilot fatigue (Aljurf et al., 2018; Jackson & Earl, 2006; Reis et al., 2013, 2016a, 2016b) to ‘non-representative’ pilot samples. However, the assumption of sample bias does not seem justified. No studies have reported lower fatigue values than Aljurf et al. (2018).

Fatigue-related performance impairments are threatening flight safety (Bandeira et al., 2018; Bendak & Rashid, 2020; Goode, 2003; Hartzler, 2014). Hartzler (2014) and Coombs et al. (2020) reported impairment of divided attention, short term memory, concentration, deteriorated psychomotor and visual performance, and generally degraded flying abilities of pilots due to fatigue. While these multimodal performance impairments are not easily measured on flight duty, microsleep events in the cockpit are valid manifestations of excessive fatigue at the controls. Fatigue-related performance impairments can be as severe as sudden in-flight medical incapacitation, e.g., due to sudden cardiac death, an acute coronary syndrome, cardiac arrhythmias, pulmonary embolism, or stroke (Simons et al., 2021), especially during microsleep events (Coombes et al., 2020). Although pilot unions have been warning about rising levels of pilot fatigue for many years, regulators have not reacted. According to the recent research results (Aljurf et al., 2018; Coombes et al., 2020; Williamson & Friswell, 2017), microsleep events on the flight deck are fairly frequent, although flight time limitations (FTL) and FRM (FRM) should prevent microsleep and excessive fatigue in the cockpit. When accumulated sleep debt (ICAO, 2015) cannot be recovered before commencing flight duties, on-duty sleepiness and more accumulated fatigue can impair the sensory, cognitive, physical, and behavioral functions of flight crews (Coombes et al., 2020; Hartzler, 2014). In addition to higher propensity to fall asleep, fatigued pilots tend to make more errors of omission and commission, their judgement, decision making ability and short term memory degrades, their mood deteriorates, pilots’ irritability is higher, and pilots’ flying skills degrade (Coombes et al., 2020; Hartzler, 2014). These complex, multimodal performance decrements are difficult to measure during active flight duties, but microsleep events on the flight deck are valid manifestations of excessive fatigue and sleepiness. Incapacitation during microsleep events are functionally similar to medical incapacitations due to a heart attack or a stroke (Coombes et al., 2020; Simons et al., 2021). Full situation awareness is essential for flight safety (Kharoufah et al., 2018), but when a pilot accidentally falls asleep at the controls, situational awareness is gone, then pilots need time for full reorientation on the flightdeck: How much time has elapsed since nodding off? Where are they exactly (position and altitude)? What do the primary flight display and other instruments indicate? Are all instruments and avionics working properly? How many calls of the air traffic controller have they missed? Have they infringed a controlled airspace without properly announcing their approach to the air traffic controller? If pilots were woken up by the master caution or another system failure warning, the outcome of this microsleep event would almost certainly be fatal for all persons on board. In other words: If both pilots accidentally doze off at the same time, the safety relevant situation awareness and redundancy completely disappears. Coombes et al. (2020) reported 1.1 cases within 2’000 flight hours, where both pilots accidentally fell asleep at the controls on the flight deck, without prior coordination, and 7.3 cases of one pilot’s microsleep in the cockpit every 1000 flight hours. In May 2022, a scandal made headlines. While the first officer was taking his controlled rest (EASA FTL, 2014), the captain (and pilot-in-command) did not respond to the air traffic-controller's call, allegedly because he had fallen asleep at the controls. The captain was immediately fired for this unintentional nap3, although microsleep events in the cockpit are reported by 45% of pilots (Aljurf et al., 2018; Williamson & Friswell, 2017), two-thirds of the investigated pilots reported fatigue-related errors during active flight duty. These facts suggest that FTL and FRM (FRM) are less effective than expected (Bourgeois-Bougrine, 2020; Coombes et al., 2020; Demerouti et al., 2019; Efthymiou et al., 2021). But how could we come so far? Fatigue should have been prevented by legally binding FTL, and FRM should have proved exceptions going beyond FTL, to allow or prohibit them. Working time regulations must be designed to maintain occupational health and safety (ILO, 2019a, 2019b), but this is not the case (Aljurf et al., 2018; Coombes et al., 2020; Reis et al., 2013, 2016a, 2016b).

The following part will address potential weaknesses regarding ‘standard methods’ of fatigue studies and FRM, as recommended by ICAO, EASA and other regulators. First of all, the traditional fatigue study setup will be discussed.

1.4.1 Research Questions of Traditional Fatigue Studies

Traditional fatigue studies have typically been commissioned and funded by airlines. The feasibility of the airline's planned flight operations should be assessed, to meet mandatory or voluntary FRM obligations. These studies, e.g., focused on “Sleep on long-haul layovers and pilot fatigue at the start of the next duty period” (Cosgrave et al., 2018) or similar topics (Gander, Mulrine, et al., 2014; Sallinen et al., 2018). Th study of Holmes et al. (2012) illustrates the research question and study setup. “This study provides a practical example of FRM in aviation. The sleep and sleepiness of 44 pilots (11 trips ×4 pilot crew) working an ultra-long-range (ULR; flight time >16 h) round-trip operation between Doha and Houston was assessed. Sleep was assessed using activity monitors and self- reported sleep diaries. Mean Karolinska Sleepiness Scores (KSS) for climb and descent […] The results indicate that the operation is well designed from a fatigue management perspective.” (Holmes et al., 2012, p. 27).

Most of the published fatigue studies were designed to prove the feasibility of the intended flight operation, which usually goes beyond the already questionable FTL in terms of ultra-long-range flights or special route pairings. Although fatigue studies were published as peer reviewed research projects, the research question was usually not really open (Holmes et al., 2012; M. van den Berg et al., 2016; M. J. van den Berg et al., 2020). It was clear from the start that the study funding airlines, e.g., Singapore Airlines, Delta Airlines, etc. wanted to implement their planned flight operations. This as well as the researchers’ expectations regarding results may have influenced pilots’ responses until a certain point, as explained in the next paragraphs.

1.4.2 Potential Modification of Behavior and the ‘Hawthorne’, or ‘Rosenthal Effect’

Before the start of fatigue studies, pilots were informed about the study purpose and setup. They were told that their behavior, particularly PVT performance, fatigue or sleepiness levels, sleep diaries, sleep and rest times, would be documented in detail. Pilots could theoretically also be subject to closer scrutiny throughout and after the research project. The fatigue studies usually lasted several days or weeks. Participating pilots may have communicated with each other and with the researchers. Pilots might also have adjusted their behavior to their employer’s standard operating procedures (SOPs) and FRM recommendations, in line with the ‘Hawthorne-Effect’ (Ulich, 2001). The ‘Rosenthal Effect’ (e.g., Innes & Fraser, 1971; Rosenthal & Fode, 1963), or experimenter’s expectation effect refers to artifacts, based on the experimenter-subject relationship, by which certain expectations, attitudes, beliefs and positive stereotypes of the experimenter become a ‘self-fulfilling prophecy’. Both, the ‘Hawthorne’ and the ‘Rosenthal Effect’, describe potential changes in behavior, attributed solely to the subject's awareness of being under observation as part of a study or experiment, without the experimenter expressly directing concrete, increased performance requirements or other expectations of them. Of course, pilots know the implicit expectations of their airline management and the purpose of ‘fatigue studies’. The subjects’ expectations, a potential suspicion of deception, how subjects interpret the question and assess expected results, can influence their reaction tendencies in the direction of social or management’s desirability. Therefore, the representativeness of the pilots’ behavior in these studies could well be questioned. The granted confidentiality may also be questioned by participating pilots, given the effectiveness of pilots’ modern ‘bush-drums’ (WhatsApp).

1.4.3 Representativity of the Investigated Pilot Samples

Another issue of conventional fatigue studies is the questionable representativeness of the investigated pilot samples. When studies reported high levels of accumulated fatigue (e.g., Aljurf et al., 2018; Reis et al., 2013, 2016a, 2016b), or when studies reported widespread burnout, symptoms of depression and/or anxiety among pilots (Aljurf et al., 2018; Cahill et al., 2021; Cullen et al., 2020; Johansson & Melin, 2018; AC. Wu et al., 2016 ), experts immediately attributed these results to bias in sample selection and lack of representativeness. Considering the ethical standards of research involving humans, and the described method of recruiting pilot samples, the representativeness of the pilot sample in traditional fatigue/sleepiness studies is highly questionable (e.g., Cosgrave et al., 2018; Gander et al., 2013; Gander, Mulrine, et al., 2014; Holmes et al., 2012; Wu LJ et al., 2018). First of all, pilots had to suit the selection criteria (e.g., being an active pilot, no vacation or sick leave or pilot training in the last month or year, or whatever researchers prescribed). Then the pilots meeting the selection criteria for the actual study were informed about study purpose and applied methods. Then, these suitable pilots had to agree to participate on a voluntary basis. Many pilots had their reasons, why they refused to participate. The participating pilots might have had their own reasons and motivations to take part in a study. In these airline-funded studies, pilots had to share personal data with the study authors (actigraphy, sleep diaries, documented work and rest times, PVT performance tests over several weeks etc.). Pilots may have thought that their data (to a certain degree) was also accessible to airline management. Pilots also had to sign an informed consent form. Thus, the promised anonymity may have been questionable anyway. Since the author of the dissertation knows the pilot population and their extremely effective ‘bush-drums’ very well (often being at the receiving end), the author is convinced that many fellow pilots knew immediately who was taking part in this study and why. This contradicts the described granted confidentiality.

Moreover, since no representative random sample (i.e., control group) was tested and compared with the participating pilot sample, a selection bias and lack of representativity of the finally investigated pilots could never be excluded (Cosgrave et al., 2018; Gander, Mangie, et al., 2014; Holmes et al., 2012; Sallinen et al., 2013; M. van den Berg et al., 2016). Sample selection biases in previous fatigue studies were never discussed or even mentioned, although – according to study purposes – eligible pilots generally participated on a voluntary basis (in line with ethical research standards). Only Sykes et al. (2012) discussed the potential sample selection bias of his study, where pilots’ mental health was investigated in context with the renewal of their medical class 1, in a non-anonymous setting. The participating pilots were on average younger and healthier than the total available pilot sample.

Therefore, the representativity of the participating pilot sample can generally not be guaranteed for available fatigue or pilot mental health studies. More methodical issues are discussed in the next paragraphs.

1.4.4 Fatigue and Sleepiness Self-Reports

KSS and the Samn-Perelli-Scale measure one symptom with one item: acute sleepiness in the last minutes before the item is rated. The single-item or ‘scale’ is ordinal, not metric or interval-scaled. In addition to this limitation, it is not clear, how pilots on flight duty differ between e.g., 4 and 5, or 6 and 7, since no objective references are given. Oken et al. (2006) and Hartzler (2014) reported, that humans often cannot reliably assess their alertness/sleepiness: While their EEG objectively measured stage 1 or stage 2 sleep, some subjects could still respond to stimuli and reported being awake (Oken et al., 2006).

Fatigue, in contrast to sleepiness, refers to mid- and long-term consequences of long duties or workdays or worknights, restricted sleep, resulting exhaustion and impairment of everyday functioning at work and/or in private life. Sleepiness is a key symptom of fatigue and was described as an increased tendency to fall asleep after long hours of wakefulness or sleep deprivation due to low psycho-physiological arousal (Shahid et al., 2010). In addition, subjective measures like rating sleepiness with the KSS, or Samn-Perelli scale or ESS (Johns, 1991; Johns MW, 1992) could be skewed toward socially or occupationally desirable responses, in line with the ‘Hawthorne’, or ‘Rosenthal Effect’ (Ulich, 2001). The discovery of the Hawthorne Effect originally led to the realization that human performance – and probably also alertness/sleepiness – are not only shaped by objective working conditions and duty hours, but also to a large extent by social factors (Ulich, 2001). Really objective psychophysiological measurements such as ultra-high resolution heart rate variability (HRV) measurements would be more reliable and valid than subjective assessments on flight duty.

1.4.5 Measuring the Symptom Sleepiness vs. the Complex Construct of Fatigue

In traditional fatigue studies, the terms sleepiness and fatigue were used as synonyms, neglecting the complexity of the construct accumulated fatigue, in contrast to alertness/sleepiness (Shahid et al., 2010). Sleepiness was often measured with the Karolinska Sleepiness Scale (KSS) (Åkerstedt & Gillberg, 1990) or the Samn-Perelli-Scale fatigue scale. The KSS measures subjective sleepiness with only one item (1=extremely alert to 9=extremely sleepy/fighting sleep). The KSS was validated in a laboratory setting (Kaida et al., 2006), not on flight duty. Other studies used the Epworth Sleepiness Scale (ESS, Johns, 1991; Johns MW, 1992).

Åkerstedt et al. (2021) investigated “Acute and cumulative effects of scheduling on aircrew fatigue in ultra-short-haul operations”, looking at cumulative effects across seven duty days in a row. However, seven consecutive days of flight duties are by no means enough to measure accumulated fatigue, especially not with the KSS. Burnout research implies that accumulated fatigue and exhaustion develop over months and years, not over one week (Demerouti et al., 2019; Fanjoy et al., 2010).

The ICAO definition of fatigue does not explicitly differ between sleepiness, fatigue, accumulated and pathologic fatigue. The International Civil Aviation Organization ICAO (2015) defines fatigue as: “A physiological state of reduced mental or physical performance capability resulting from sleep loss, extended wakefulness, circadian phase, and/or workload (mental and / or physical activity) that can impair a person’s alertness and ability to adequately perform safety-related operational duties.” The International Classification of Diseases (ICD-11) defines Fatigue (MG22) as: „Feeling of exhaustion, lethargy, or decreased energy, usually experienced as a weakening or depletion of one’s physical or mental resource and characterized by a decreased capacity for work and reduced efficiency in responding to stimuli. Fatigue is normal following a period of exertion, mental or physical, but sometimes may occur in the absence of such exertion as a symptom of health conditions”. Sleepiness is one key symptom of fatigue, whereby acute and accumulated fatigue can cause long-term impairment of human performance and health, as explained by the Theory of Allostasis and allostatic load (McEwen, 2004, 2006; McEwen & Karatsoreos, 2015; McEwen & Stellar, 1993).

Shahid et al. (2010) differ explicitly between sleepiness and fatigue and describe sleepiness as an increased tendency to fall asleep after long hours of wakefulness or sleep deprivation, similar to (Hartzler, 2014). Short-haul flight operations with several take-offs and landings (sectors) per flight duty were reported to be the most fatiguing (Honn et al., 2016; Jackson & Earl, 2006; Reis et al., 2016a; Roach, Sargent, et al., 2012; Vejvoda et al., 2014). Nevertheless, traditional fatigue studies focused on long-haul and ultra-long-haul flights with augmented crews – a rare and comfortable situation for pilots. With four pilots (incl. one ‘take-off crew’ and one ‘relief crew’), or a ‚relief pilot’, one crew or one pilot can always consume their or his/her coordinated rest (to sleep or rest) during a long flight. This way all pilots can arrive well rested at their destination.

‘Physiological’ or normal sleepiness is caused by daily activities, usually lasts a short period and is relieved by compensatory rest. Fatigue in the sense of exhaustion is an integral part of burnout and describes feelings of emptiness, feeling overwhelmed by work, a strong desire for rest and a state of psychophysiological exhaustion (Demerouti et al., 2019; Fanjoy et al., 2010; Pallich et al., 2021). Any definition of pilot fatigue must relate to safety critical performance impairment due to fatigue (EASA FTL, 2014; ICAO, 2015). The implications of accumulated fatigue must be included, e.g., pilots often report feeling drained and tired even after regular sleeping opportunities or legal rest periods. Pilots affected by accumulated fatigue generally tire more quickly, although pilots – as all humans – may not be fully aware of their fatigue level (Hartzler, 2014; Oken et al., 2006). Fatigue related health impairment (burnout, physical and mental health impairment) must also be considered in times when most pilots report severe or excessive fatigue, in line with the Theory of Allostasis (McEwen, 2004, 2006, 2008; McEwen & Karatsoreos, 2015; McEwen & Stellar, 1993; Sapolsky, 2004).

In this thesis, fatigue was measured with the Fatigue Severity Scale (FSS, Krupp et al., 1989) to obtain data comparable to Reis et al. (2013, 2016) and Aljurf et al. (2018). Although the Fatigue Severity Scale was originally developed to measure fatigue of patients with chronic diseases, e.g., multiple sclerosis, clinical sleep disorders, patients after stroke etc. (Valko et al., 2008), the FSS seems to be more suitable to measure accumulated fatigue than the KSS (Åkerstedt & Gilberg, 1990) or ESS (Johns, 1991; Johns MW, 1992).

Alertness and high motivation to perform excellent work is essential for smooth and safe flight operations, this is why the item “My motivation is lower when I am fatigued” is highly relevant for pilots. Therefore, pilots should not be impaired by fatigue in their professional life, where monitoring tasks as well as conscientiousness and diligence (i.e., to check 20 to 200 pages of coded notice to airmen, called NOTAMS, decipher and keep in mind generally coded meteo-briefings of one or more continents for a whole day) are highly safety relevant. Beyond alertness/sleepiness ratings, Dawson & McCulloch (2005) simply and aptly summarized: “Managing fatigue: It's about sleep”. Therefore, the next paragraphs will focus on sleep and how it is measured is traditional fatigue studies, as recommended by ICAO (2011, 2015).

1.4.6 The Use of Actigraphy to Measure Sleep

Quality and quantity of actual sleep are essential to predict or avoid fatigue (e.g., Dawson & McCulloch, 2005; Hartzler, 2014). ICAO (2015) recommend actigraphy to measure, or much more imply sleep and rest. Fatigue studies explained the applied methods like this, “Sleep was monitored (actigraphy, duty/sleep diaries) from 3 days before the first study trip to 3 days after the second study trip” (Gander et al., 2013, p. 697). How well sleep can be monitored with actigraphy remains questionable, because actigraphy was originally developed to measure activity in terms of steps or other types of distinct movement, while the actimeter is attached to the non-dominant hand. Actigraphy can only estimate quantity of sleep, but neither sleep quality nor sleep efficiency, which are essential for recovery (Hartzler, 2014).

Actigraphy was proven to be rather unreliable for subjects with sleep problems, especially for assessing sleep latency and time awake after sleep onset (Kandera et al., 2019; Taibi et al., 2013; Wang et al., 2008). Actimetry cannot reliably differentiate between time in bed with little movement (e.g., when individuals lie or sit awake, reading, watching tv, trying to fall asleep again) and actual sleep (time with little movement during sleep). Reliability of different acitmeters can also differ considerably (Kandera et al., 2019). Actigraphy most likely cannot provide a complete picture of pilots' sleep, considering that 30% to 50% of the pilots reported suffering from more or less severe insomnia or other sleep disorders such as sleep apnea (Aljurf et al., 2018; Alzehairi et al., 2021; Reis et al., 2016b).

Van den Berg et al. (2016) stated, that self-reported sleep duration can be as reliable as actigraphy, if rest or sleep is implied between ‘light off’ and ‘light on’, and if sleep efficiency or the quality of recovery is not deemed relevant. Actigraphy and implied sleep during scheduled rest periods seem too unreliable for pilot fatigue studies, since many pilots reported considerable sleep problems, frequent sleep restrictions and other fatigue risks associated with flight duties (Aljurf et al., 2018; Alzehairi et al., 2021; Reis et al., 2013, 2016b).

Biomathematical models (BMM) such as BAM (Ingre et al., 2014) build on the traditional methods of measuring fatigue and imply algorithm-based calculated off-duty sleep times. Problems associated with this and other issues with BMM are described in the next paragraphs.

1.4.7 Biomathematical Models (BMM)

Commercial air operators rely on the assumption, that legal rosters, based on FTL and FRM, are safe for aircrews and flight operations, especially when BMM or rostering software are used for crew planning. BMM try to predict, how much sleep aircrews would likely get on different route pairings and layovers, and how efficient and safe pilots would likely be on duty (Cabon et al., 2012; Dawson et al., 2017; Dorrian et al., 2012). Dorrian et al. (2012) reported low reliability of BMM for predicted sleep, even for sleep patterns on the same or matched layovers.

EASA’s study of the effectiveness of FTL also reported different fatigue predictions of two evaluated BMM for the exact same analyzed rosters (European Commission, 2019). Methodical issues about validity and reliability of the multidimensional outputs of BMM (Bourgeois-Bougrine, 2020; Cabon et al., 2012; Dawson et al., 2017; Dorrian et al., 2012) and empirical evidence of high levels of fatigue in most pilots (Aljurf et al., 2018; Reis et al., 2013, 2016a) suggest, that FTL, the legal basis of aircrews’ rosters, and widely used BMM should be improved. The settings of the BMM programs can be changed as required, e.g., to achieve maximum productivity (maximum duty and flight hours/month and minimum rest), or to protect pilots’ health.

Many studies have used the Psychomotor Vigilance Test (PVT) by Dinges & Powell (1985) to measure pilot reaction speed, and accuracy. This test was validated in a sleep laboratory setting as quite reliable to measure fatigue related performance decrements (Basner et al., 2011; Dinges & Powell, 1985; Graeber & Dinges, 1994). Potential problems associated with this performance test on flight duties are described in the next section.

1.4.8 Psychomotor Vigilance Test (PVT) to Measure Fatigue Related Performance Decrements

The Psychomotor Vigilance Test (PVT by Dinges & Powell, 1985) is a simple response time and accuracy task, where dots occur randomly at intervals of 2 to 10 seconds. They must be detected and reacted to as fast as possible, pushing a button. The PVT was evaluated as highly sensitive for fatigue measurement in controlled laboratory settings (Basner et al., 2011; Kaida et al., 2006; Zeeuw et al., 2018). Almost all pilot fatigue studies used PVT to measure performance impairment due to fatigue or sleepiness of pilots. The PVT may be valid and reliable in experimental sleep laboratory studies, which measure performance decrements after controlled sleep deprivation etc. (Basner et al., 2011; Kaida et al., 2006; Zeeuw et al., 2018), but the simple PVT seems less reliable for professional pilots on duty: Pilots have developed coping skills to manage their performance despite fatigue, because falling asleep or making mistakes can quickly become fatal on flight duty – for pilots, cabin crews and passengers on board. In addition to that, the very simple PVT does not represent pilots’ tasks in the cockpit (Hartzler, 2014). Pilots must monitor their avionics and flight management systems, as well as radiotelephony or data-link communication, while they check if all systems are working correctly, and display indications are plausible. Pilots’ tasks on the flight deck are much more complex than the PVT, therefore also more tiring. It is not surprising that the PVT results are inconsistent across fatigue studies: Studies reported that pilots performed significantly better, equally good or significantly worse, when utmost fatigue was expected, like at top of descent (TOD) (Åkerstedt et al., 2021; Gander et al., 2013; Gander, Mulrine, et al., 2014; Hartzler, 2014; Holmes et al., 2012; Sallinen et al., 2017, 2018; M. van den Berg et al., 2016). A more sophisticated approach to measuring pilot performance should provide better insight into pilot performance under severe or excessive sleepiness or fatigue, like proposed by Rosa et al. (2020).

1.4.9 Flight Time Limitations and Working Time Arrangements in General

Legal working time arrangements must be designed to prevent severe fatigue and must support occupational health and safety (ILO, 2019a, 2019b). FTL (flight time limitations) represent the working time regulations for aircrews. Therefore, the aviation industry would have good reasons to expect, that FTL for pilots and cabin crews are healthy and safe, and that they could be used to the maximum limits, like most companies outside aviation do. The ICAO definition of fatigue focuses on acute on-duty sleepiness in terms of circadian and homeostatic sleep-drive (Hartzler, 2014; Zeeuw et al., 2018), and potential safety critical performance impairment because of fatigue (Bandeira et al., 2018; Bendak & Rashid, 2020; Bourgeois-Bougrine, 2020; Goode, 2003). Neither high on duty sleepiness nor excessive fatigue could be prevented by FTL and FRM (Aljurf et al., 2018; Reis et al., 2013, 2016a, 2016b).

1.4.10 Conclusions

The traditional methods of fatigue studies, as they are recommended by ICAO and regional regulators (e.g., EASA FTL, 2014; ICAO, 2015), have obvious weaknesses. EASA’s present evaluation of the effectiveness of FTL uses these weak, unreliable and hardly valid methods, much to the detriment of the aircrews and flight safety (Åkerstedt et al., 2021; EASA, 2019). On-duty sleepiness and fatigue should be understood as different constructs. The general principles and scientific evidence of work psychology and burnout research, as well as clinical psychology and occupational medicine should be integrated, when talking about the psychophysiological construct fatigue. If more researchers had a look at pilots returning from flight duties, to see how tired pilots look on their way from the cockpit, the inconvenient results of referenced studies should be taken seriously (Aljurf et al., 2018; Feijo et al., 2012; Jackson & Earl, 2006; Johansson & Melin, 2018; Reis et al., 2013, 2016a).

1.5 The Relevance of Pilots' Physical and Mental Health for Flight Safety and Regulatory Authorities

Before a prospective pilot can begin his first flight lesson, he must complete an aeromedical check. An Aeromedical Examiner (AME) examines and certifies the physical health and also the mental suitability of a prospective private or professional pilot. Prospective commercial pilots must be in good health for their Class 1 medical certification, according to medical standards for flight crew licensing (Part-MED, 2011; Part-MED, 2019; CAR, 2015; FAA, 2022). After the first medical class 1, pilots must renew their medical certificate on average every year, older pilots up to twice per year, and generally after serious illness or surgeries. According to MED.B.055 and MED.B.060 (Part-MED, 2019), any mental health issue can lead to long-term or final withdrawal of professional pilots’ medical certification and final lay off. Commission Regulation (EU) 2018/1042 states, that “Crew members are not to carry out duties on an aircraft when under the influence of psychoactive substances or when unfit due to injury, fatigue, medication, sickness, or other similar causes.” This EASA regulation was published three years after the Germanwings crash (BEA, 2016), and specifically mentioned fatigue and mental health of flight crew members as potential risks to flight safety. Possible interactions between fatigue and mental health are not explicitly addressed, but they are not ruled out, either.

Professional pilots represent an originally healthy working population. Professional pilots’ mental and physical health is crucial for flight safety, to prevent sudden incapacitation in flight due to a heart attack or stroke on the flight deck (Groner et al., 2022; Gudmundsdottir et al., 2017; Pukkala et al., 2003; Simons et al., 2021; Zeeb et al., 2010), or another ‘Germanwings’ (BEA, 2016), ‘LAM’ (MWT, 2016) or eventually Western China disaster (2022). Several studies have reported considerable impairment of professional pilots’ physical health and higher mortality of airline pilots (Nicholas et al., 1998; Sykes et al., 2012; Zeeb et al., 2010). Other studies have reported high levels of fatigue among active pilots (Aljurf et al., 2018; Jackson & Earl, 2006; Reis et al., 2013, 2016a, 2016b), or reported considerable mental health issues (Aljurf et al., 2018; Feijo et al., 2012; O’Hagan et al., 2017, 2019; Pasha & Stokes, 2018; Widyahening, 2007; AC. Wu et al., 2016), which should be generally prevented by selection, medical certification, ergonomic working conditions and healthy work and rest times. This was not the case before this PhD research started, based on the available body of peer reviewed publications. Therefore, work-related and psychosocial stress, pilots’ actual rosters, sleep problems, fatigue, mental health and well-being became the focus of this research, as well as their potential correlations and interactions, in line with the Theory of Allostasis (Chen et al., 2014; McEwen, 2004, 2006, 2008; McEwen & Karatsoreos, 2015; McEwen & Stellar, 1993; Sapolsky, 2004). The extent of positive screening results for symptoms of depression and anxiety, common mental disorders4, impaired well-being, significant sleep problems and severe to excessive fatigue were also of interest, in comparison with previous research.

1.6 A Pilot’s Life – Decades ago and Today

About thirty years ago there was the dream job of being a pilot. Young aspiring pilots got their pilot training fully funded by their airline/employer, and they got a nice salary during their pilot training. Almost every pilot, who successfully completed his skill and theory tests, was also offered a pilot position with a solid employment contract. Back then, pilots earned a lot of money, flew to attractive holiday destinations, stayed there for several days or a week – paid by their employer – and enjoyed a lot of free time on their rest and standby days. Of course, many people envied the pilots' seemingly amazing lifestyle and excellent salaries. Most non-pilots do not know how living and working conditions of pilots have deteriorated up until today. A former President of the European Pilots Association (ECA), Dirk Polloczek, explained at an EASA safety conference, how pilots’ working conditions have deteriorated, particularly for low-cost carrier (LCC) pilots.

Work-related and psychosocial stressors could adversely affect the physical and mental health of pilots (McEwen, 2004, 2008; McEwen & Stellar, 1993; Sapolsky, 2004; Widyahening, 2007), and will be described in the next part.

1.6.1