Fatigue

If you’ve ever been a new parent, a graveyard shift worker, or burdened by an untreated sleep disorder such as insomnia, you know what it’s like to try and get through the day without enough sleep. You’re tired and feeling out of sorts, and caffeine and sugar have become your two best friends. It’s easy to tell ourselves we’re fine, but if we don’t get enough of it, or if our sleep is interrupted, we will suffer from fatigue.

As pilots, it’s critical for us to be aware of how we’re feeling, and to recognise the impacts of flying whilst in a fatigued state. This article will explore the different types of fatigue, how it affects our performance, and what we can do to combat and mitigate it.

What is Fatigue?

We all lead busy lives, and factors such as long days, stress, late nights, and illness can all cause us to feel drowsy, weary, or sleepy. Fatigue can be very apparent when we feel it, but we may not always be able to see it coming, which can cause issues when trying to prevent it. There can often be confusion between tiredness and fatigue; when someone says they are tired, they may already be in a fatigued state, but what’s the difference?

Tiredness happens to everyone - it's an expected feeling after certain activities or at the end of the day. Usually, you know why you're tired, and a good night's sleep solves the problem. Fatigue, however, manifests itself as a daily lack of energy; unusual or excessive whole-body tiredness that’s not relieved by sleep.

From a flying perspective, ICAO defines fatigue as:

'a physiological state of reduced mental or physical performance capability resulting from sleep loss or extended wakefulness, circadian phase, or workload (mental and/or physical activity) that can impair a crew member’s alertness and ability to safely operate an aircraft or perform safety related duties’.

Types of Fatigue

There are three types of fatigue: transient, cumulative, and circadian.

Circadian fatigue refers to reduced human performance whilst working during night-time hours, for example shift workers.

Transient fatigue is acute fatigue brought on by extreme restrictions to sleep or being awake for a prolonged period over one or two days; the effects of transient fatigue can generally be resolved by a good night’s sleep.

Cumulative fatigue is brought on by repeated mild sleep restrictions or extended hours of being awake across a series of days. Research shows that to recover from cumulative fatigue a person will need to sleep for longer than usual over a number of days. One good night’s sleep is very unlikely to result in someone no longer feeling the effects.

Our sleep-wake cycle

The following diagram illustrates the typical daily sleep-wake cycle. It is the pattern of time we spend awake and asleep every 24 hours and shows the crucial role of consolidating sleep overnight to meet the 'sleep need’, which (should) help you to stay awake and function normally during the day as the ‘sleep need’ builds again.

The ‘sleep need’ (also called Homeostatic sleep pressure) can be affected by physical or mental stress, long hours spent awake or other factors such as illness, which may result in an increase or demand in the ‘sleep need’. If that demand for more sleep is not met, it will likely lead to fatigue. A healthy sleep-wake cycle is achieved when your body’s circadian rhythm and ‘sleep need’ are optimally synchronised, helping you to feel refreshed and alert and able to perform well during the day. Both the quantity and quality of sleep are of equal importance. Inadequate sleep over several nights causes a sleep ‘debt’ that can only be recovered with adequate sleep.

How fatigue affects flying performance

Fatigue affects both our mental and physical performance, especially tasks that require hand-eye coordination, rapid reaction times and fine motor skills, such as piloting an aircraft. It can also affect attention, vigilance, concentration, communication, and decision-making, leading to fatigue-related errors. Other factors that will lead to an increased fatigue state are issues such as stress, dehydration, and illness. Fatigue can also be brought on by low arousal or a lack of stimulus. All of these are very much pertinent to flying activities. 

Katy Lee, Airline Pilot and Human Factors expert recently joined our Workshop on Human Factors. During the Workshop we found out that being awake for 20 hours has the same effect on our bodies and decision-making as being well over the legal drink-driving limit.

Fatigue will impair our alertness, which may result in inaccurate flying, missed radio calls, or incorrect procedures. Most likely, our reaction times will be slower than normal, memory items will be harder to recall, our Situational Awareness will be reduced, and overall, we’re more likely to make errors that we wouldn’t normally make with the resulting consequences.

Combating Fatigue 

Often, we are too tired or exhausted to recognise the fatigued state we are in, but if there is any doubt, it must be taken seriously. Colleagues, family, and friends will likely point it out quite openly if you don’t seem to be 100%, and we should do the same with our fellow pilots if we see they are looking fatigued.

As highlighted in our Stress Management article, the use of the mnemonic ‘IMSAFE’ is a helpful pre-flight planning tool with the ‘F’ standing for Fatigue; again, it’s very easy to give a cursory answer to this and be dismissive, but it should be considered carefully and answered truthfully. Fatigue should be addressed during the preparation phase for flying; we may well notice it the moment we get out of bed that morning and should therefore think about rescheduling the flight altogether. 

The second thing we can do is manage it appropriately. Whilst the use of caffeine may help, if we are really fatigued, caffeine will only mask, not solve the issue. To nap or not to nap? Research shows that taking frequent naps will ‘recharge’ the body but it may not be practical. It’s easy to say it, but if you are feeling the effects of fatigue, don’t go flying! A better approach is to stay away and get a good night’s sleep then fly another day.

The third thing we can do is to work to prevent it. Ideally, we should all think ahead and look after ourselves such that fatigue doesn’t become an issue. You can do this by eating well and staying hydrated and making sure you’re getting enough regular sleep.

Key takeaways:

·       Use the IMSAFE mnemonic in your pre-flight preparation and be honest about how you’re feeling – it’s better to be on the ground having postponed a flight than to be in the air and regretting it.

·       If you make an error due to fatigue, why not confidentially report it through Chirp? You could save another pilot from making the same mistake who may not be so lucky.

·       Look out for your fellow pilots at the airfield who may be unknowingly suffering from fatigue.

·       To prevent fatigue, get into a good sleep routine, aiming for eight hours of sleep per night:

o   Eat well and stay hydrated.

o   Avoid caffeine and alcohol within four or five hours of bedtime.

Further reading 

https://skybrary.aero/articles/fatigue

https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/fatigue_aviation.pdf

https://www.sleep.org/how-sleep-works/sleepwake-cycle