Lost Sleep – Compromised Safety

One of the often neglected but vital predisposing physiological factors in aviation is sleep, rather lack of sleep. The commercial pilots are governed by their duty schedule and the military aviators have the uncertainties of the operational deployment to blame for the loss of sleep. Although there may be regulations and guidelines, including FDTL to ensure adequate sleep and rest for the aircrew, adequacy of sleep remains largely self reported. So also, it is largely affected or influenced by individual pilot’s personal and professional commitments. Here, it is pertinent to know that changing sleep pattern over a period of time is known to induce cumulative fatigue and sleep debt. This, though subtle or covert, have broader implications for aviation safety.

Airline pilots continue to cope with irregular work schedule to meet their professional commitments. In addition, their lifestyle and the flight schedules determined by the airlines’ commercial considerations may result in  prolonged hours of work. Military pilots too, driven by technological advances and changing strategies, have to cope with sustained operations, through the day and the night over a prolonged period. Such situations of prolonged operational commitments, lead the aircrew to cope with reduced hours of sleep over several days.

Another oft neglected aspect is that sleep loss is known to occur amongst pilots during the productive phase of their lives, coinciding with an active phase of social activities, including marriage, rearing young children and socialising with families and friends. Such a lifestyle, of professional, social and personal commitments, contributes to chronic sleep restriction. Sleep deprivation has been reported to affect cognitive, psycho-behavioural and emotional measures [1, 2, 3]. This interaction of the sleep pattern, of prolonged hours of wakefulness late into the night with making do with reduced hours of sleep, may have adverse affects on performance [4].

It may be stated that the observational studies on sleep loss, including reported incidents and accidents statistics, do not provide converging evidence to the laboratory studies on sleep/wake pattern proving performance deterioration due to sleep loss alone [5]. Yet it is prudent for the pilots to know that an increase in error rate or delayed reactions have been reported by individuals due to sleep loss. This is important since the variables in aviation – time of the day, circadian rhythms, alertness states and the task may not only compromise the performance but increase the susceptibility of the pilots to loss of situational awareness.

Effect of acute or cumulative sleep loss are known to affect the central nervous system, reaction time, vestibular system or memory. Specifically, sleep loss impairs memory, learning, logical reasoning, arithmetic calculations, pattern recognition, verbal processing and decision making [6]. The prefrontal lobe, responsible for attention, coping with novel and unknown situations, divergent, innovative and flexible thinking based on past experiences, contextual and temporal memory, shows slowing of its activity due to sleep loss [6].

This must be noted that the cognitive activities of prefrontal lobe are vital in dynamic tasks such as aviation. In aviation, the safety of the flight and the success of the mission (for commercial and military pilots, respectively) depends on the cognitive performance [6]. The cognitive performance, in turn, is the sum total of encoding, evaluating, assessing, calculating, updating and acting thereon on the ever-changing set of  audio-visual information. Such situations are further compounded by a variety of stressors on the pilots, which may have an interactive affect on performance [6].

Variables commonly known to affect information processing and cognitive function are sleep loss, time pressure and workload. These variables adversely affecting the cognitive ability, therefore, are an ever-present threat to mission and flight safety. This is all the more relevant to understand after the tragic crash of the Air India flight IX 812 on 22 May 2010, where the captain was reported to be sleeping in flight, and may have had adverse effects of sleep inertia (‘groggy’) while attempting to land at Mangalore on the ill-fated day.

Whether one agrees or not, it is important for the individual pilots to sleep adequately. So also the airlines must plan adequate rest periods while defining the crew roster as well as choosing noise free hotel accommodation, including hotels, for its crew to ensure that they sleep well before they report for duty. Regulators too have an onerous responsibility for ensuring that airlines and pilots both follow a scientifically designed FDTL.


1. Mertens HW, Collins WE. The effects of age, sleep deprivation, and altitude in complex performance. Human factors 1986; 28:541-51

2. Naitoh P, Townsend RE. The role of sleep deprivation research in human factors. Human Factors 1970;12:575-85

3. Pilcher JJ, Huffcutt AL. Effects of sleep deprivation on performance: A meta-analysis. Sleep 1996; 19:318-26

4. Spencer MB. The influence of irregularity of rest and activity on performance: A model based on time since sleep and time of day. Ergonomics, 1987;30(9): 1275-86

5. De Vries-Greiver AHG, Meijman TF. The impact of abnormal hours of work on various modes of information processing: A process model on human costs of performance. Ergonomics 1987; 30: 1287-99

6. Lichacz FMJ. Examining the effects of combined stressors on dynamic task performance. The International Journal of Aviation Psychology 2005; 15(1): 45-66

Acknowledgement: Image courtesy www.freedigitalphotos.net

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