Flight crews, like other people, are subject to physical and emotional stressors which contribute to fatigue.
The International Civil Aviation Organisation (ICAO) defines fatigue as a physiological state of reduced mental or physical performance capability resulting from sleep loss, extended wakefulness, circadian phase, or workload that can impair a person’s alertness and ability to perform safety-related operational duties.
High levels of flight-crew fatigue significantly increase the potential for pilot errors.
Fatigue is particularly prevalent among pilots because of unpredictable work hours, long duty periods, circadian disruption and insufficient sleep.
These factors can occur together to produce a combination of sleep deprivation, circadian rhythm effects, and "time-on task" fatigue.
Regulators seek to mitigate fatigue by limiting the number of hours pilots are allowed to fly over varying periods of time.
It has been estimated that four-seven per cent of civil aviation incidents and accidents can be attributed to fatigued pilots.
"In the last 16 years, fatigue has been associated with 250 fatalities in air carrier accidents," said Robert Sumwalt, NTSB vice chairman, at a Federal Aviation Administration (FAA) symposium in July 2016.
Symptoms associated with fatigue include slower reaction times, difficulty concentrating on tasks, resulting in procedural mistakes, lapses in attention, inability to anticipate events, forgetfulness and reduced decision-making ability. The magnitude of these effects is correlated to the circadian rhythm and length of time awake.
Performance is affected the most when there is a combination of extended wakefulness and circadian influences.
According to the US Centre for Disease Control (CDC) circadian rhythm is the internal biological clock that regulates body functions based on our wake/sleep cycle. It can be disrupted by changes in sleep pattern. Flight crews can experience circadian-rhythm disruption (specifically jet lag) as they work.
Flight crews often operate aircraft across time zones. This can affect their internal biological clock and disrupt normal sleep patterns, which can lead to fatigue, difficulty sleeping, changes in mood, stomach and intestinal symptoms and other health problems.
Although travellers who suffer circadian disruption after a single flight recover after one-two weeks, flight crews are continually exposed and show evidence of chronic circadian-rhythm disruption. Some flight crews may have higher exposure to circadian disruption than most of their co-workers and may be at greater risk for possible health effects.
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There are a number of global organisations, such as NASA Ames, that do aeromedical research into flight-crew workload and fatigue.
An FAA study of 55 human-factor aviation accidents from 1978-1999 concluded that the number of accidents increased proportionally to the amount of time the captain had been on duty. The accident proportion rela
