What is fatigue?

Fatigue, within a human factors context, can be defined as "1, physical or mental weariness resulting from exertion", which, at least physiologically, is expressed as "3, the decreased capacity or complete inability of an organism, an organ, or a part to function normally because of excessive stimulation or prolonged exertion" (all meanings by The American Heritage Dictionary, 20091).

A detailed explanation of fatigue in aviation embedded from YouTube on 16 August 2012

Fatigue could be considered as a symptom of medical problem but, more commonly, it is a physiological reaction due to exertion, lack of sleep, boredom or even a change in sleeping cycles. Excess fatigue arising from sleep loss, circadian disruption, and other factors tends to decrease alertness, impair performance, and worsen moods. Therefore, it may be expected to influence the performance, health, and safety of people.

Fatigue can be classified into two areas:

  • Physical fatigue, due to the inability to continue functioning at the level of one’s normal abilities.
  • Mental fatigue, which can surface through decreased wakefulness, also known as somnolence, or just as a general decrease of attention. Fatigue becomes important in aviation when efficiency is reduced or performance is impaired (Hawley, 19974).

Although estimates vary, official statistics indicate that fatigue is involved in at least 4-8% of aviation mishaps. Lyman and Orlady (1980) showed that fatigue was specifically implicated in 77 (3.8 percent) of 2,006 incidents reported by pilots to NASA’s Aviation Safety Reporting System (ASRS). When the ASRS analysis was expanded to include all factors that could be directly or indirectly linked to fatigue, incidents potentially related to fatigue increased to 426 (21.2 percent). Major problems with statistics relating fatigue to accidents and incidents include the lack of a coherent definition of fatigue itself and the absence of a reliable and valid assessment tool to measure it retrospectively. Fatigue is generally difficult to investigate on a systematic basis and to code in databases. Therefore, any statistics related to fatigue and incidents/accidents are likely to be an underestimate and should be interpreted as such (Skybrary, 20105).

What causes fatigue in pilots?

There are several factors which cause pilots to be fatigued.
These factors consist of: jet lag, disturbed sleep, high workload, the in-correct use of drugs and unresolved stress.


Fatigued pilot Image embedded from The Pacific Northwest Islander on 17 August 2012

Jet lag

Jet lag occurs when circadian rhythms are desynchronised. Our body has many body rhythms which include internal body temperature rhythm, the sleep-wakefulness rhythm and the digestive rhythm (Robson, 2008). These rhythms have the constancy of around 24 hours and thus called the circadian rhythms, as in latin circa is about and dies is day (Robson, 2008). Jet lag is experienced because of these rhythms being desynchronised as a result of flying through different time zones (Robson, 2008). This effects sleep as the body takes time to re-adjust so a pilot may be awake when he/she is supposed to be asleep or vice versa. Lack of sleep is a very common cause of fatigue (Immune health solutions, 2012). Therefore, long-haul pilots can experience fatigue due to jet lag on a regular basis. Jet lag is more evident in people travelling from west to east since the length of day that their internal body rhythm expects is shortened. The body can stand better the change in time if the length of day is lengthened which happens if one travels from East to West. These flights cause Jet Lag because they involve travelling through different time zones and because of this travelling from South to North or vice versa does not cause Jet Lag because the time zone is same throughout the travel in these cases.

Sleep disruption

Disruption in sleep is a very common cause of fatigue among pilots. Pilots have a very restricting schedule which they have to abide by; which accounts for very little sleep. Sleep disruption can be caused by insomnia which is the inability to fall asleep or having difficulty to sustain sleep (Merrill & Zieve, 2011). This can occur due to jet lag – crossing different time zones. It is very likely that some long haul pilots could suffer insomnia as they cross several different time zones which in turn affect their sleep-wakefulness cycle. Insufficient sleep or disrupted sleep can cause sleep deprivation which effectively results in the pilot to feel fatigued. Short haul flights also can cause disruptions to the sleeping patterns of pilots whose first flight of the day starts very early in the morning as such is the case in flights that require to report before 7am. Under circumstances as this, the pilot is forced to attempt sleep before the normal bed time his body is used to. Due to the body's internal biological clock, the pilot will find it difficult to sleep and this makes it complicated since it is just as if he was still awake and towards the morning, when he has just found sleep comfort, he is forced to wake up at a very unfortunate time when his body is mostly recovering from the previous day's stress. As he wakes up, he has a sleep debt and if this pattern continues for several days, the sleep debt accumulates leading to fatigue on the pilot's behalf (Stokes & Kite, 1994).

High workload

High workload can be considered as having to perform many tasks in a confined space of time. Pilots have to deal with many pieces of information at a single time which makes their task of flying very arduous. It is crucial that pilots are alert and up to date with all the information in order to carry out a safe flight. In a high work load environment of the cockpit it is quite possible for pilots to experience mental and physical fatigue. However, it is very important that the workload is managed in an efficient and effective manner to prevent the occurrence of fatigue.

Use of drugs and medication

Drugs are commonly used by individuals to induce relaxation and sleep. Many of these drugs have adverse effects on the quality of ones sleep and without correct monitoring and advice by an aviation medical examiner, have no place in the aviation environment. Alcohol is a particularly common example. While sleeping after a session of heavy drinking, may give the illusion of a deep sleep, this is not the case. The sleep cycle is altered and the sleepers REM cycle is reduced (Hawkins & Orlady, 1993; Robson, 2008). REM sleep is vital for a pilots mental rejuvenation. Caffeine is often used to offset the urge for sleep, and reduce tiredness by pilots on long shifts. Depending on the time and the amount of caffeine consumed, it can also have negative effects on their sleep. While it may temporarily increase alertness, like alcohol, it later reduces REM sleep. Therefore the use of drugs can lead to and increase the effects of fatigue. (Hawkins & Orlady, 1993).


Stress is a natural part of everyday life and it involves direct and in-direct stressors. In aviation the physical act of flying, the aircraft's cockpit environment, the weather and workload are the direct stressors. The in-direct stressors include the pilots work situation and their home/family life (Ewing, 2008). On-going unrelieved stress and the feeling of inability to cope will lead to fatigue (Ewing, 2008). Insomnia, an inability to sleep, is also often linked to unresolved stress. On-going insomnia or unrelieved stress can lead to sleep deprivation (Robson, 2008).

How can fatigue be overcome?

Fatigue can be overcome by sufficient sleep, exercise, a balanced diet (Portenoy & Miaskowski, 2007), medication and with use of relaxation techniques. It is important to get at least the recommended eight hours of sleep (Robson, 2008). Sufficient sleep is among one of the best remedy for fatigue. Having rest periods between flights can aid the pilot in staying alert in the cockpit and thus battling the symptoms of fatigue. A decent amount of exercise keeps the body fit and healthy and therefore helps prevent fatigue. Eating a balance diet is also very important as it ensures that our body receives the right nutrients that it needs to function optimally thus helping toward preventing fatigue. Various medications can be used to combat fatigue provided that it doesn’t interfere with the pilot’s cognitive or physical abilities. Therefore, fatigue can be prevented and cured. It has also been proven that to better combat fatigue, a person travelling across different time zones who is likely to suffer fatigue through jet lag can minimise the likelihood of being fatigued if he or she sticks to his usual daily timings. This means that a pilot who travels from say the east to the west coast of the United States should sleep at the time he usually sleeps in the east coast rather than trying to sleep according to the new time zone he is in. This works best for people who will stay in the new area for a short time such as pilots. It helps pilots to feel exactly the same as if they are still in their homes.

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Fatigue in Aviation



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