Since World War II, flight
operations have been increasingly performed over longer distances,
longer intervals, and across multiple time zones. The biology
governing the performance of men and women has not changed, however.
The timing, quality and quantity of sleep needed may vary among
individuals, but among all people, unalterable physiological needs
Efforts are being
made within aerospace to design and employ behavioral and
pharmacological interventions to overcome the effects of fatigue and
sleepiness in personnel required to operate in a sleep-deprived
condition and at times when they would normally be sleeping.
Accidents are caused by human
error 80% of the time. The role of fatigue and circadian rhythm
disorders (desynchronosis) in these mishaps is probably
underestimated. Recognition of the causes and signs of fatigue is
central to safe and effective air operations.
The tendency to sleep cycles
over a 24-hour period. Maximal sleepiness occurs between 0600 and
0800. Although not as imposing, another episode of sleepiness occurs
between 1400 and 1600. Adaptation to a new time zone or shiftwork
pattern takes up to 3 weeks, depending on individual differences,
the frequency and magnitude of the time shifts. Various
environmental (light, activity) and social factors (sleep habits,
social interactions, work schedule) may either assist or prevent the
accommodation to a new schedule.
Sleepiness and fatigue cause
reduced ability to function. Lapses (the failure to respond to a
situation) increase. Lapses may be associated with microsleeps
(episodes of sleep lasting 0.5 to 10 seconds) but can also occur
without sleep onset. The four sleep-related factors involved in
fatigue-induced performance impairments are the circadian phase of
the biological clock, the presence of acute sleep loss, the presence
of cumulative sleep loss and the presence of sleep inertia. Lapses
increase 2 to 10 times during night operations without pre-existing
sleep loss. Acute sleep loss (following a single night of sleep
loss) results in 4 to 10 times more lapses, while chronic sleep
deprivation by reducing sleep 2-3 hours per night for 1 week may
increase lapses by 3 to 5 times normal. Sleep inertia is the
difficulty awakening from a sleep episode. Sleep inertia results in
increased lapses and is most likely to be present after abrupt
awakenings and awakening from stages 3 and 4 NREM sleep.
The potential for catastrophe
due to lapses is enormous. An aircraft going 250 kts on a glide-path,
for example, can travel over 400 feet during a 1-second lapse.
Micro-sleeps have been shown to occur in aircrew during landing
approaches in commercial carriers.
The degree of resulting
fatigue and risk of mishaps are dependent on the type of aircraft,
mission, operations schedule, and environmental conditions.
Increased workload and turbulence tend to exacerbate the effects of
sleep loss and jet lag. Reaction times may be markedly slowed, which
can be critical when rapid reactions are necessary. False responding
also increases, i.e. the pilot may take action when no action is
warranted, especially when aware of having missed signals. The
resulting anticipation of another event and over attention on
individual signals or problems further reduces situational
awareness. Fatigue increases calculation errors, logical errors, and
ineffective problem solving. The member is less able to think of new
solutions and repeatedly tries the same approach to a situational
Memory deficits progressively
worsen with fatigue and sleep loss. The sleepy and tired crewmember
reads or hears instructions repeatedly but cannot retain the
information, leading to critical errors and uncertainty about the
status of the situation. Performance variability results from
increased lapses and errors of omission. Although the member often
becomes aware of the shortcomings in performance and responds by
trying to increase self-motivation and effort, performance
improvement is short-lived. He/she may perceive the operation as
more stressful and tiring as the effort continues. Ultimately, the
crewmember's motivation to perform well and avoid risks erodes.
No individual is immune to the
effects of sleep loss and fatigue, although there are individual
differences in the ability to tolerate sleep loss. After one night
of sleep loss, half of healthy individuals perform reasonably well,
but the remainder exhibit moderate to severe performance deficits.
After 36 hours, there is little difference between individuals in
their ability to perform-all have severe performance deficits.
The ability of a fatigued
crewmember to self-assess alertness is also limited. In fatigued
individuals, initial good performance early on may give a false
sense of security. As time goes by, performance deteriorates. A
crewmember is also more likely to overestimate his or her ability to
perform if asked about being tired or able to perform. Relief from
other crewmembers when signs of fatigue are observed (eyelids
drooping, yawning, irritability, forgetfulness) is crucial.
Every flight operation has its
own tempo, time required to perform the major tasks, personnel
structure, and number of personnel. There are a number of different
aerospace scenarios, ranging from mundane short- and long-haul
ferrying operations, to combat and space flight. Prevailing cultural
attitudes may pose a hindrance to adequate resting and napping. Our
society now sleeps about an hour less on average than our ancestors
a century ago. Sleep and the demand for productivity are at odds,
and adult napping is virtually frowned upon.
Extensive government research
into fatigue has yielded important information about techniques to
improve performance and safety during prolonged and/or night-time
flying. Basic principles to keep in mind are listed below. Naps are
defined as intentional sleep lasting less than half the length of
the major sleep period.
- Do not overwork or
under-sleep before flying
- Naps taken before and at
the beginning of flights at night improve performance.
- Two nights of normal sleep
before flying greatly improve performance.
- Two nights of normal sleep
at the end of an operation are necessary to recover from the
effects of sleep deprivation.
- A night off in a long
series of night operations helps restore function.
- Naps are possible during
the day, especially in the mid-afternoon sleepiness phase.
- Naps are a stopgap approach
to improve performance and safety for limited periods of time, not
an indefinite substitute for long sleep periods during biological
- Make an attempt to anchor
sleep when sleeping in a different time zone by getting some of
the sleep during home base sleeping hours.
- The longer the nap, the
better the improvement in performance.
- The longer the nap, the
longer it takes to awaken (more sleep inertia).
- Longer and harder
operations require more napping.
- At least 20 minutes should
be allowed to awaken from a nap to allow dissipation of sleep
- Noise and activity help
dissipate sleep inertia.
- When possible, engage in
conversation, stretch, and move about to improve alertness.
- Caffeine can help maintain
alertness but may disrupt sleep if used too close to desired sleep
- Alcohol use may interfere
with sleep quality and performance.
- Napping will not promote
circadian adjustment to night flying.
- Relaxation techniques and
sleep hygiene can assist napping and adjustment to a new circadian
- The napping environment
should be as free as possible from noise, light, temperature
extremes, and interruptions.
- Lying down and sleeping is
more beneficial than trying to sleep with chest elevated.
- Maintain a meal schedule
with healthy and nutritional food to minimize gastrointestinal
problems associated with night operations.
Stimulants and sedatives are
currently used in US military and foreign commercial operations.
There may be a role for stimulants such as modafanil, pemoline,
methylphenidate, and amphetamines in defined settings. The same is
true for short- and intermediate-acting sedatives. Even short-acting
sedatives can impair next-day performance, however, and reasonable
concerns exist about the effect of stimulants on sleep, emotions,
and performance. For the time being, though, US private pilots and
flight crews are prohibited from using medications discussed above.