Fatigue is really a catchall term for a variety of different subjective experiences. In the context of flight operations, crewmember fatigue becomes important if it reduces efficiency or otherwise impairs crew performance. There are two systematic physiological causes of fatigue (and poorer performance) –sleep loss and circadian rhythms- both of which are affected by flight operations. The NASA Fatigue Countermeasures Program focuses on these factors.
Sleep and Sleep Loss
Like food and water, sleep is a physiological need vital to human survival and critical to human existence. Sleep loss can be additive and can result in a cumulative sleep debt and also leads to increased waking sleepiness. Sleep loss and sleepiness can decrease physical, psychomotor, and mental performance, and can increase negative mood and decrease positive mood. Therefore, a principal consequence of sleepiness resulting from extended duty or altered work/ rest schedules is an increased vulnerability to performance decrements –like the effects of alcohol- and it has been suggested as a contributory factor in many accidents and catastrophes. So sleep loss and sleepiness should be taken seriously. Most individuals are more likely to be sleepier than they report or experience.
Some factors affecting sleepiness are the prior sleep, the circadyan phase, the age, the medical conditions, the medications, the alcohol and the work conditions. We are physiologically programmed for two periods of maximal sleepiness in a usual 24-hour period. The period 3-5 A.M. is a circadian low point for temperature, performance, and alertness. The other period of increased sleepiness is roughly 3-5 P.M. These windows can be used to schedule sleep periods or naps because the brain provides a period of maximal sleepiness and an increased opportunity for sleep.
Circadian rhythms are the second physiological factor that affects fatigue in flight operations. The expedient (but incorrect) assumption that we can do function equally at any time of the day or night underlies many activities in our society. Without any timing information from the environment, the biological day is about 25 hours and the circadian clock in the brain coordinates daily cycles –sleep/ wake, performance, temperature, hormones, digestion, etc. However, if they are not all synchronized appropriately, the harmony rapidly degenerates into disorder. In everyday life, synchronization of an individual’s circadian clock to a 24-hour day depends on a combination of different inputs, like sunlight, work/ rest schedules and regular social interaction.
We cannot, as yet, reset our circadian rhythms at will, as we do our wrist watches. It may take days to weeks for all rhythms to synchronize to a new time zone after one transmeridian flight. Thus, flight crews seldom become fully synchronized to local time during layovers. According to some studies by DLR, NASA and the Royal Norwegian Air Force Institution of Aviation Medicine, some factors affecting circadian adaptation are:
Takes longer the more time zones are crossed.
Faster after a westward flight –delay direction- or with progressively later duty times because the biological day is usually longer than 24 hours.
Different people adapt at different rates.
“Evening-types” adapt faster than “morning-types”.
Ability to adapt decreases with age.
Effect of Flight Operations
But also flight operations play a role in creating flight crew fatigue. They are not always conducive to a regular sleep/ wake schedule. Flight operations can affect sleep and circadian factors in two main ways: first, by occuring at unusual or changing times in the day/ night cycle, and second, by requiring successive time-zone changes.
An obvious contributor to sleep loss is a prolonged period of continuous wakefulness. An extended duty period can create fatigue by extending wakefulness and decreasing sleep, and can involve circadian disruption. Other fatigue factors that can emerge in continuous operations are boredom and complacency.
In many flight operations, the time available for sleep is restricted by a variety of constraints. If an individual’s physiological timing for sleep does not coincide with the scheduled sleep opportunity, then a cumulative sleep debt can result.
Some fatigue signs and symptoms are:
- Forgetful - Fixated
- Poor decisions - Apathetic
- Slowed reaction time - Lethargic
- Reduced vigilance - Bad mood
- Poor communication - Nodding off
There are many misconceptions about fatigue in flight operations. Some commonly held misconceptions, according to what we have presented above, are: “scheduled rest period allows for required sleep”, “I know how tired away”, “I’ve lost sleep before and I did just fine”, “I’m motivated enough to just push through it” or “One cure will work for everyone, all aircraft, all flight schedules”.
In view of that, NASA presents some recommendations to deal with fatigue during flight operations.
Alertness Management Strategies
These recommendations should be tailored to an individual’s particular needs and activities. You should experiment with different strategies and evaluate their effectiveness in the context of your own physiology and specific flight operations. The best effects may result from combining strategies rather than relying on an individual strategy.
NASA differentiates two kind of Alertness Management Strategies, Preventive Strategies and Operational Strategies:
Preventive Strategies: used before duty and on layovers to reduce advers effects of fatigue, sleep loss, and circadian disruption during flight operations.
Sleep scheduling and quantity:
At home: get the best sleep possible before starting a trip.
On a trip: try to get at least as much sleep per 24 hours as you would in a normal 24-hour period at home.
Trust your own physiology: if you feel sleepy and circumstances permit, then sleep; and if you wake spontaneously and cannot go back to sleep within 15-30 minutes, then get up.
Strategic napping, before duty:
A nap can accutely improve alertness.
If immediately before a duty period, limit nap to 45 minutes.
If you sleep too long and go into deep sleep, it may take longer for you to become fully awake.
When you nap at times other than immediately before a duty period, then the nap can be longer
A nap will decrease the length of continuous wakefulness before a duty period; some sleep is better than none.
Good sleep habits:
Keep a regular sleep/ wake schedule, protecting sleep time; develop and practice a regular pre-sleep routine; use bedroom only for sleep, avoiding work, worry and exercise; if hungry, eat a light snack; avoid alcohol or caffeine before going to bed; use physical/ mental relaxation techniques as needed to fall asleep; if you don’t fall asleep in 30 minutes, get out of bed.
Take care of the sleep environment: dark and quiet room, comfortable temperature and comfortable sleep surface.
Take care of your lifestyle: do exercise regularly –but not too near bedtime- and eat a balanced diet.
Operational Strategies: used in flight to maintain alertness and performance. It is a FAR requirement that “…each required flight crewmember on flight deck duty must remained at the assigned duty station with seat belt fastened while the aircraft is taking off or landing, and while it is en route”. So, what can we do?:
Engage in conversations with others, do something that involves physical action and take regular stretch breaks.
Strategic caffeine consumption: use caffeine to acutely increase alertness; don’t use it when already alert –e.g. start of duty or after a nap-; and avoid caffeine near bedtime.
Be sensible about nutrition and stay hydrated –remember that caffeine is a diuretic and contributes to dehydratation.
Plan brief nap during long-haul flights -for low-workload portion at cruise, up to 40 minutes in duration, one crewmember at a time, three-person non-augmented flights.
So take your fatigue seriously, apply a tailored combination of these NASA recommendations and improve your performance during flight operations.