FATIGUE

Fatigue is a complex physiological state characterized by a lack of alertness and reduced mental and physical performance, often accompanied by drowsiness.

FATIGUE in AVIATION

The main causes of fatigue in aviation are:

• Amount, timing, and quality of sleep each day (sleep/wake schedule),
• Amount of time since last sleep period (continuous hours awake),
• Time of day (circadian rhythm),
• Operations through multiple time zones, and
• Workload and time on task.

Fatigue Mitigating Strategies

The staff can manage fatigue before, during and after work shifts by using a range of fatigue mitigation strategies that work for their personal sleep needs. It is helpful to establish effective sleep habits, such as:

• scheduling sleep
• trying a quiet activity before bed
• establishing a bedtime routine
• not eating or drinking too much
• getting out of bed if they cannot sleep
• using relaxation techniques
• having a comfortable bed

Adequate nutrition and hydration is also important for managing and preventing fatigue. Ideally, the crew member should:

• have a balanced diet
• eat regularly
• have healthy snacks
• eat breakfast
• plan meals
• drink water regularly
• avoid late night meals (which result in slower digestion).

Mitigation Strategies for Managing Sleep Debt

Sleep restriction is common across different types of flight operations. Because the effects of sleep restriction are cumulative, schedules must be designed to allow periodic opportunities for recovery. Recovery opportunities need to occur more frequently when daily sleep restriction is greater, because of the more rapid accumulation of fatigue.

Restoration of a normal non-REM/REM cycle is one measure of recovery from the effects of sleep loss. Lost sleep is not recovered hour-for-hour, although recovery sleep may be slightly longer than usual.

• On the first recovery night, there is more slow-wave sleep than usual. Indeed, there can be so much slow-wave sleep that there is not enough time to make up REM sleep.
• On the second recovery night, there is often more REM sleep than usual.
• By the third recovery night, the non-REM/REM cycle is usually back to normal.

Operationally, this means that schedules need to periodically include an opportunity for at least two consecutive nights of unrestricted sleep, to enable crewmembers to recover from the effects of sleep loss.

Mitigation Strategies for Night Duty

Night duty forces crew members to sleep later than normal in their circadian body clock cycle. This means that they have a limited amount of time to sleep before the circadian body clock wakes them up. Consequently, they need to get to sleep as soon as possible after coming off duty.

Getting off duty earlier increases the time available for sleep in the morning, before the circadian body clock makes it difficult for crewmembers to stay asleep.

Napping before going on duty is beneficial to help maintain alertness and performance through to the end of the night

Napping during the duty period (for example, on ground while aircraft are being loaded and unloaded) is beneficial to help maintain alertness and performance through to the end of the night. The napping opportunity should be limited to 40-45 minutes, with an additional 10-15 minutes allowed to ensure that sleep inertia (if any) has dissipated.

Mitigation Strategies to Minimize Sleep Interruptions

Because uninterrupted non-REM/REM cycles are the key to good quality sleep, operators should develop procedures that minimize interruptions to crewmembers’ sleep.

Rest periods should include defined blocks of time (sleep opportunities) during which crewmembers are not contacted except in emergencies. These protected sleep opportunities need to be known to flight crews and all other relevant personnel. For example, calls from crew scheduling should not occur during a rest period as they can be extremely disruptive.

Operators should also develop procedures to protect crewmember sleep at layover and napping facilities.

Augmented crew

With appropriate in-flight resting facilities, crew can rotate rest times and share facilities to manage their fatigue.

It is important that crews consider that with an augmented crew, there will be variability in terms of alertness and circadian (i.e. time zone/body clock) adjustment among crew members. Additionally, they will all have different sleep needs and different performance effects from countermeasures (e.g. caffeine). When utilizing in-flight rest facilities, a crew member should do so intelligently, rather than doing something potentially stressful, the crew member should make use of the time to relax and attempt to sleep.

There are various studies which look at the effects of sleep inertia on performance, particularly when awakening from deep sleep. Operators and crews should be aware of and manage the effect of sleep inertia in flight operations.