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Flying Fatigued: Fatigue in Aviation

Updated Monday, 27 November 2023

Commercial pilots must assess whether they are 'fit to fly' - but some personal and commercial pressures mean they can sometimes fly when fatigued, which can be dangerous. What's being done to manage this?

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Take a look at these two case studies:

Case Study 1

1994 ‘OASIS’ BOEING 737-2D6C, 7T-VEE, COVENTRY airport, UK link for full report

On 21 December 1994, a B737 had been leased by Phoenix Aviation (from Air Algerie) to transport live animals from the UK to France and Netherlands. At 06:42, the airplane departed Amsterdam to Coventry. The weather worsened at Coventry with RVR reducing to 700m and unable to receive the RWY23 ILS due to not being to an updated 40 channel ILS standard. Consequently, an SRA approach was flown to 0.5miles from touchdown and then a go around was initiated. After entering the hold, RVR reduced to 600m and the crew diverted to EMA. At 0900, RVR improved to 1200m and overcast at 600ft and so the crew departed EMA to attempt another SRA approach for RWY23. There was some confusion about correct headings (e.g., mistaking 010deg for 100deg) and the aircraft descended below the Minimum Descent Height (MDH) in patchy foggy conditions and collided with an 86ft high (291 ft ams) pylon located on the extended centreline of RWY23 (1.1. miles from the threshold). Major damage to the left wing caused the aircraft to roll uncontrollably to the left, impacting the ground followed by an intense fire resulting in all 5 fatalities.


One of the findings of this case study is that the performance of the flight crew was impaired by the effects of tiredness after completing 10 hours of flight duty during the night during 5 flight sectors which included a total of 6 approaches to land. The flight crew’s duty started at 2345L and they departed their first sector at 0059L. The Air Algerie Flight Time Limitation (FTL) scheme for night duties had a maximum duty period of 7hrs 45 minutes on 4 sectors or more. DEA Crew, regardless of sectors, are limited to 8hrs between 2200-0559L.

The crew permitted the aircraft to descend significantly below the normal glide path on the SRA to RWY23 in patchy foggy conditions. The descent was continued below the Minimum Decision Height (MDH) without the appropriate visual reference to the approach lighting or the RWY threshold. SRAs are regarded by Jeppersen as a ‘final option’ if all other pilot-interpreted approach aids are unavailable. On a 5th sector, over 10 hours of flight duty time, at night, with foggy conditions, an SRA was another stressor for pilots to contend with. 

Poor weather/visibility and pilot fatigue may increase the risk of disorientation and loss of situational awareness.

The final flight was very short, and the crew found themselves with insufficient time to complete the normal flight deck procedures. The company’s Standard Operating Procedures (SOPs) were not adhered to; cross checking the altimeter height indications during the approach was not observed and the MDH was not called out by the non-flying pilot.

Until this accident, Crew Resource Management training was only conducted for newly appointed First Officers and involved a short briefing on the concepts of CRM. Current Captains were not given any CRM training.

Case Study 2

BOMBARDIER DHC-8-402, S2-AGU, BS211, KATHMANDU, NEPAL link for full report

On March 12, 2018, a US Bangla Airlines, Bombardier DHC-8-402, S2-AGU, flight number BS211 departed Hazrat Shahjalal International Airport, Dhaka, Bangladesh at 06:51 UTC on a scheduled flight to Tribhuvan International Airport (TIA), Kathmandu, Nepal. At 0834UTC, on a VOR approach at Tribhuvan International Airport (TIA), Kathmandu, Nepal, at 0834UTC, they crashed about 442 meters southeast of the touchdown point of runway 20, just outside the inner perimeter fence of the aerodrome. All 4 crew members (2 cockpit crew and 2 cabin crew), and 45 out of the 67 passengers were killed during accident. The aircraft was destroyed by impact forces and a post-crash fire. 

S2-AGU, the aircraft involved, seen in July 2014S2-AGU, the aircraft involved, seen in July 2014.


Many factors contributed to the accident: improper pre-flight briefings, PIC fatigue due to lack of sleep, failure to adhere to Standard Operating Procedures (SOPs), failure to perform briefings, poor Crew Resource Management (CRM), very steep cockpit gradient, Pilot In Command (PIC) fixation to land at any cost (even after realising the aircraft was not configured to land), lack of simulator training, failure to meet stabilisation criteria. Contributing to this, the aircraft was offset to the proper approach path that led to manoeuvres in a very dangerous and unsafe attitude to align with the runway. There was no attempt made to carry out a go around. The report states that “landing was completed in a sheer desperation after sighting the runway, at very close proximity and very low altitude”. The core explanation seems to result from the mental health condition of the PIC.

Medical history of PIC showed he was declared unfit to fly in 1993 due to his medical condition (depression). He was later cleared medically in 2002. The PIC was still harbouring severe mental stress. The effect of stress was evident with the fact that he was irritable, tensed, moody, and aggressive at various times. This is probably the reason for his undue aggressive behaviour and anger aimed at ATC personnel as well as operation staff (FO). Reasons for his actions could be him trying to prove FO (whom he had a conflict with) that he is a very competent pilot and would be able to safely land the aircraft in any adverse situation.

As discussed in the previous articles, the job of a pilot requires a great deal of responsibility for ensuring the overall flight safety of the passengers, crew, and the aircraft itself. This means that they must be physically and mentally ‘fit to fly’ and is often a responsibility that is left to the decision of the pilot. An acronym IM SAFE is a tool to assist pilots in identifying whether they are physically and mentally fit to fly.

This includes decisions based around one’s physical health. This can include declaring any medication, recognising stress (e.g., life events or accumulative daily hassles) which may impact a pilot’s performance, alcohol limits (20mg of alcohol/100ml blood), a no drugs policy, mental and physical fatigue levels (well rested), emotions and eating (good nutrition).

Therefore, pilots must only fly when ‘fit to fly’. It is important to learn to say “No”, before aeromedical examiners, employers or fellow pilots say, “You do not look ‘fit to fly’. “I will not fly with you” or “I will not let you fly that fatigued.” Nonetheless, research suggests that high numbers of professional pilots may be severely fatigued and still flying (Venus, 2020). As we can see from the case studies, there can be complex, personal, professional, and commercial reasons pressuring pilots to fly while feeling fatigued.

What is Fatigue?

Fatigue is both mental and physical which can be brought on by performing a demanding activity. It is linked to concentration, sleepiness, and vitality. It is not just about ‘tiredness’; you might not feel like sleeping but this doesn’t mean you have the energy to complete daily or complex tasks (Fulghum Bruce, 2023). ICAO 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” (ICAO, 2013).

Regulation (EC) No 216/7(f): No crew member must allow their task achievement/decision making to deteriorate to the extent that flight safety is endangered because of the effects of fatigue, inter alia, fatigue accumulation, sleep deprivation, number of sectors flown, night duties or time zone changes. Rest periods must provide sufficient time to enable crew members to overcome the effects of the previous duties and to be well rested by the start of the following flight duty period.

Types of Fatigue

There are three types of fatigue:

  • TRANSIENT fatigue is acute fatigue brought on by extreme sleep restriction or extended hours awake within 1 or 2 days.
  • CUMULATIVE fatigue is fatigue brought on by repeated mild sleep restriction or extended hours awake across a series of days.
  • CIRCADIAN fatigue refers to the reduced performance during night time hours, particularly during an individual’s “window of circadian low” (WOCL). The period called the Window of Circadian Low (WOCL) is when someone is operating between 4am – 6am where alertness is at its poorest and body temperature at the lowest. Night duties typically disrupt biological rhythms where it is more difficult to stay alert. Bodies need both rest and sleep. Napping can help reduce sleep debt but should not be used regularly to replace normal sleeping behaviour (Eurocontrol, 2018).

Fatigue usually results in impaired standards of operation with increased likeliness of error including reduced reaction time, reduced attentiveness, impaired memory, and withdrawn mood. Fatigue may manifest itself for a pilot through inaccurate flying, missed radio calls, symptoms of equipment malfunctions being missed, routine tasks being performed inaccurately or even forgotten. In extreme cases, communication is reduced, short-term memory can be impaired and falling asleep - either a short "micro-sleep" or for a longer period - can result in poor decision making (Staff Reporter, 2018; Eurocontrol, 2018).


Research demonstrates that the accumulation of "sleep debt", e.g., having an hour less of sleep for several consecutive days, needs a series of days with more than-usual sleep for a person to fully recover from cumulative fatigue.

Flight Time Limitations (FTLs)

Commercial pilots adhere to FTL (CAP371). Whilst FTL schemes can be restrictive, schemes do not prevent pilots from becoming tired. FTL schemes only consider the time element of duty and the number of sections flown. No adjustments are made for ambient weather conditions, types of approaches made, or other stressors (e.g., technical issues) which can add to the amount of fatigue experienced by flight crew during flight. Disrupted sleep patterns over the longer-term lead to poor health outcomes and performance can deteriorate.

Ask yourself if you are fit to fly? For example, am I yawning, blinking excessively, making simple errors, and/or forgetting things?

Mental Wellbeing

Mental wellbeing is essential to the safe operation and performance of a pilot. There are many mental health conditions, such as grief, depression, anxiety and panic disorders that are common. These can develop and become exacerbated with chronic fatigue, burnout, and unresolved stress. CAA data shows that only 1% of pilots who reported mental health issues went on to lose their license for good.

Cullen (2020): 5669.pdf (

Identifying Mental Health

Five significant warning signs of mental health risk. A pilot may exhibit one or more of the following symptoms (SkyBrary).

  • A change in personality, acting like a different person, not acting or feeling like self
  • Uncharacteristic behaviour, heightened open displays of anxiety, anger or moodiness
  • Social withdrawal, always doing things on their own, becoming isolated
  • Lack of self-care or a tendency to display risky behaviours in public
  • A sense of hopelessness or feeling overwhelmed 

An individual who displays more than one could lead the observer to suspect that the pilot may be at risk of deteriorating mental health (SkyBrary).

  • Emotional – Pilots who are struggling with their mental health may seem irritable and sensitive to criticism, they may demonstrate an uncharacteristic loss of confidence, or seem to lose their sense of humour.
  • Cognitive – A pilot may make more mistakes than usual, have problems making decisions, or not be able to concentrate. They may display a sudden and unexplained degradation in performance, both on and off the flight deck.
  • Behavioural – This could include things like arriving late, not taking rest breaks, taking unofficial time off, not joining in flight deck banter, becoming more introverted or extroverted and generally acting out of character.
  • Physical – Pilots who are stressed sometimes exhibit physical symptoms such as a constant cold, being tired at work, looking like they haven’t tried with their appearance, or rapid weight loss or gain. 

Early detection suggests there are some effective treatment strategies (SkyBrary). If you are concerned about your mental wellbeing, then complete the:



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