Sleep is something none of us can escape from. For some it’s amazing, for others it’s annoying. Pilots, like many other people in other professions, often have to deal with staying awake while everyone else is dreaming away. Lots of recent research is revealing more and more about the effects of sleep (and the lack of) on our bodies and brains. So today, we’ll be looking at how to manage fatigue, and how we can stay safe and healthy while (sometimes literally) flying through the night.

Human error still accounts for roughly 75% of all global aviation accidents, and pilot fatigue still accounts for roughly 20% of that! Recent studies have even shown that landing an aircraft at 5 AM after a full night of flying can have a mental impairment that’s equivalent to a blood alcohol level of 0.08%.. Pretty crazy stuff right? Let’s unpack all of this step by step, and start from the beginning.

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What happens when we sleep?

Sleep is essential for us! It recharges our brains and bodies, and keeps our immune system up to speed to fight off diseases. The average amount of sleep you and I need is 7-9 hours.

However, it changes based on our age, amount of physical and mental energy we’ve used, and our individual differences in our brains.

Sleep is now finally starting to get the attention it needs in a world where so many of us are chronically sleep deprived. It turns out that the sleep – nutrition – exercise triangle actually gravitates more towards sleep than the other 2, if you want to live a healthy life.

But let’s zoom in on what’s going inside the brain when we feel sleepy, and while we’re sleeping. Why do we feel tired, and why do we (usually) no longer feel tired when we wake up?

When we are awake, our brain is having to deal with a constant increase in a chemical called Adenosine.

How to manage fatigue

Adenosine in the brain is what makes us feel more tired when it interacts with receptors in the brain that Adenosine can bind itself to:

How to manage fatigue

When this binding happens it stimulates our desire and ability to sleep.

How to manage fatigue

The act of sleeping causes the high Adenosine levels (that we built up during the day) to lower substantially throughout the night. This eventually results in waking up and not feeling sleepy once all the Adenosine is ‘used up’.

In addition to Adenosine, the other important chemical for sleep is Melatonin. Melatonin helps us fall asleep and gets created in the Pineal gland inside the brain.

This gland’s production is extremely sensitive to light. Meaning that if we expose ourselves to even a little bit of blue / bright light, Melatonin production is severely affected and sleep will become more difficult.

Keep this process in mind as we’ll come back to it in the caffeine section below.

What are Circadian Rhythms?

The amount of sleep you personally need is determined by our internal body clocks. This body clock is called the Circadian Rhythm.

Think of it as a daily regular fluctuations of variables inside your brain and body. What variables? Good question! All of these change a lot throughout one standard cycle:

  • Body Temperature
  • Blood Pressure
  • Heart Rate
  • Sensory sensitivity
  • Neurotransmitter activity

What’s interesting is that a standard cycle for us actually lasts 25 hours, not 24. The reason we are able to make 24 hours work anyway, is because we have external cues telling us what time of day it is roughly: sunrise, sunset, regular mealtimes, work schedules, etc.

These points in time are called Zeitgebers (which is German for ‘time givers’).

If we would look you up in a dark room with none of these Zeitgebers anywhere, your brain would eventually return to a 25 hour circadian rhythm, with roughly 17 hours of wake time and 8 hours of sleep!

What types of sleep are there?

There are 3 main types of sleep:

1) Transitional light sleep is the phase between putting your head on a pillow and actually falling asleep. Muscles relax, blood pressure drops, and the brain is becoming less active (or more for some people..).

2) Light NREM (Non Rapid Eye Movement) sleep is the next phase. This is usually the biggest chunk of our nights (50-60%). This is the phase where an annoying neighbour, cars, or anything else nearby has a higher chance of waking us up.

3) Deep NREM sleep is sometimes called slow-wave sleep. This is because our brainwaves slow down a lot. Heartrate and breathing slow even more, and it becomes more difficult to wake up. Deep NREM sleep is important for restoring our physical bodies. The body repairs its cells, restores functions to organs, the immune system, and bodily tissues.

4) REM (Rapid Eye Movement) sleep got its name from the fact that during this sleep phase, our eyes move rapidly in different directions. Our heart rate and blood pressure is higher, our breathing rate increases, and we start dreaming.

REM sleep is critical for our brains. The brain consolidates all the information and processes we have kept ourselves busy with before falling asleep.

It also helps transfer our acquired knowledge that was in our short term memory, into our long term memory. Without REM sleep we’d all still be trying to figure out how to make fire, not a good time!

What is Fatigue?

Fatigue happens when we as humans do not get enough opportunities to get rest and let our bodies and brains recharge.

What are the different types of fatigue?

There are 4 main types of fatigue:

1) Circadian Fatigue is the reduced performance caused by trying to function properly outside your normal circadian rhythm. The riskiest window for this type of fatigue is between 2 AM and 6 AM.

2) Cumulative Fatigue is caused by constant mild interruptions to our sleep over time (throughout a week for instance). Let’s say you have a baby that needs constant attention, a constantly changing roster, or simply noisy neighbours that keep waking you up.

3) Transient Fatigue is what happens when you stay up for a long period within 1 day, or sometimes 2. This can happen after a full night of flying, or if you’re suffering from insomnia.

4) Workload fatigue is the type of fatigue you get after a long stretch of intense work, whether mentally or physically.

What is fatigue caused by?

For pilots, the main causes for fatigue are:

  • Long duty periods
  • Poor general health
  • High workload for long times
  • Emotional stress, whether at work or at home
  • Poor lifestyle (bad nutrition, sleep, exercise, alcohol etc)
  • Reduced amount of sleep or nap opportunities
  • Working outside our circadian rhythm
  • A bad night sleep

What are the hazards caused by Fatigue?

There are quite a few hazards that are caused by pilots being fatigued:

  • Decreased mental performance
  • Reduced alertness
  • Long term health effects
  • Increased reaction time
  • Less effective memory
  • Impulsive mood

All of these reduce our ability to deal with the day to day operation, not to mention unforeseen circumstances or emergencies.

How can you recognise you are fatigued?

Recognising fatigue is extremely important when you’re working in a rapidly changing, dynamic environment. What are the main giveaways from a pilot’s perspective? Here are the main ones:

  • Forgetting earlier discussed items
  • Increased reaction time
  • Being mentally behind the aircraft
  • Micro-sleeps (falling asleep very briefly / not being in control of staying awake)
  • Alerts going unnoticed unless your FO or captain detects them
  • Sluggishness on the radio, or even completely missing calls
  • Less accuracy during manual flight

How to manage fatigue?

So what can we do to manage the risks and hazards that come with being fatigued as a pilot?

Step 1 is to ask yourself: Am I getting enough sleep in general? If the answer is no, it might be time to look into how you can increase the amount of time you give yourself to bel able to get 7-9 hours of sleep. Sleep deficit can build up and get worse over time, to the point where even getting 1 good night is still not good enough and you’ll still feel tired.

Step 2 is to take care of yourself in regards to nutrition and exercise. Fatigue is often caused by poor physical health. Dealing with this has solved various long term fatigue issues for a lot of pilots (and others who work irregular work patterns like doctors, nurses, etc).

Step 3 is making sure you create enough potential nap opportunities, if allowed during a nightshift or flight. Most OPS manuals allow for naps as long as you make sure you do not enter deep sleep, as this can cause sleep inertia in moments where your attention level should be the highest it can be. A nap that lasts 10-20 minutes is the safest way to make sure this does not happen.

Short naps, also called “Power Naps” or “NASA Naps” can massively increase performance if you feel fatigued. NASA discovered that pilots who decided to nap in the cockpit for 26 minutes, showed alertness improvements by 54%, in addition to a 34% increase in overall performance, pretty convincing results!

If you take a nap to manage your fatigue while on an off day and you’re trying to not screw up your schedule too much, avoid taking naps later in the day as this can ‘consume’ Adenosine too close to the point where you do want to fall asleep, making it trickier to fall asleep at a normal bedtime.

Have a look at the list below. By the way, the same applies to engineers, air traffic controllers, or anyone else with a role that impacts safety in any industry.

  • Adhere to your Flight Time Limitation scheme, or in the case of non-pilots, manage your working times with anything you have control over
  • CRM Training should raise awareness about the effects and causes of fatigue
  • Try to make working conditions the most pleasant you can while on duty
  • Alert and brief colleagues if you feel tired, or if you think you are behind the curve
  • Take your sleep seriously, figure out how much sleep you need (count the amount of hours you tend to sleep without an alarm), and strive to hit this amount as much as possible.
  • Limit your caffeine intake
  • Stay hydrated as much as possible
  • Only eat small portions, if you have to, if you’re working through the night

How does Caffeine affect fatigue?

Caffeine is in a lot of stuff these days. It’s loved by many for its alertness-increasing effects. But how does it work?

Remember the receptors we talked about earlier that, when interacting with Adenosine, makes us sleepy? Well, caffeine attaches itself to these Adenosine receptors as well!

So now what?

Now, the receptors are now too busy playing around with all the caffeine that binds itself to them.

You can have all the built up adenosine you want, but unless they can actually interact with the receptors, you’re not going to feel sleepy!

The problem is though, that the creation of adenosine isn’t influenced by caffeine intake. This means that there’s a buildup of adenosine, but you don’t feel the effect until all the caffeine left your system, and the receptors are freed up again:

Once the caffeine has left your system, all the built up Adenosine chemicals are like ‘Yay let’s go guys’, and they all try to attach to the now freed-up receptors at the same time, making you very very sleepy after the caffeine wears off.

This is why after a lot of caffeine, even after waking up, you might feel very drowsy!

Let’s have a look how much cafffeine your average beverages contain.

  • Your average cup of coffee: 95 mg
  • Your average cup of tea: 57 mg

The recommended maximum for the average person is about 400 mg. More than this can have negative effects on cognitive and physical functioning such as:

  • Digestive issues
  • Anxiety
  • High blood pressure
  • Heart palpitations / rapid heart rate

How to Sleep Better before a nightshift?

Good question! Here are the most proven principles for increasing your sleep quality that can also be applied to irregular working times:

  • Use a sleeping mask or black-out blinds if you need to sleep while there’s daylight around to preserve Melatonin levels

  • Use good sleep hygiene (meaning low light levels, no electronic devices before sleep, a quiet room)

  • Develop routines that help you with good habits such as exercise and taking time to unwind

  • Stick to a sleep schedule as much as you can, waking up at the same time every day on off days will still benefit your circadian rhythm consistency

  • Don’t go to bed hungry or completely full, avoid large meals right before bed

  • Create a relaxing environment with optimum lights, sounds / silence, and temperature

  • Try not to nap after 4 PM if you are trying to sleep soon after, as the nap will use up some of the Adenosine we spoke about earlier

  • If you feel mentally busy / worried / anxious, use mindfulness techniques such as yoga or meditation to clam down before sleep

  • Get more exercise to use up energy throughout the day if you feel too energetic when it’s bedtime

  • Try and stay away from sleeping tablets, as they can drastically reduce the sleep quality, and time spent in REM or NREM sleep. Currently the only sleeping tablet that is approved by the UK CAA is Temazepam, but needs to be ground tested by individuals to make sure you don’t have side effects, and always crosscheck this with your company’s policies, procedures, and OPS Manuals.

  • For long haul flights, keep in mind that it takes your system a full day in a new time zone to shift your circadian rhythm by about 90 minutes

  • For nightshifts specifically, there are two options of sleep management:
  1. Set the alarm early the night before so that when it’s early afternoon you’ll have a sufficient Adenosine level go attempt to daytime sleep.
  2. Go to bed late the night before, wake up late on the day of the upcoming nightshift, relax as much as possible during the afternoon so you will still have enough energy to complete the night shift without additional sleep.

Accidents and incidents caused by fatigue

There have been plenty of fatigue related accidents in the past:

1) A US based Night Air Ambulance Helicopter LOC-I crashed due to pilot fatigue in 2018

2) An Alaska Air Ambulance crashed with pilot fatigue as a main contributing factor in 2017

3) TriMG Boeing 737-300 from Singapore to Jakarta Halim accidentally taxied onto the active runway without a clearance in 2020. The final report included:

“The captain’s statement noted that he had not attained any appreciable sleep in the 24 hours preceding the flight. “

4) A superjet 100 crash in 2013 was crashed during a test flight that was linked to pilot fatigue

Here is an excellent article on 16 fatigue related aviation incidents.

Lessons learnt from “Why We Sleep” by Neuroscientist Mathew Walker

I heavily recommend “Why We Sleep” by Mathew Walker. He’s an experienced Neuroscientist with a PhD in Neurophysiology from the Medical Research Council in London, UK.

After lots of recommendations from the doctors I work with as a HEMS pilot, I decided to read it. In HEMS, we fly a lot at night, and deal with a Day-Day-Night-Night- 4 off roster, which can be fatiguing at times. Here are my main take-aways from his research and experiments:

  • Natural sleep is always better than medically aided sleep (pills, drinks, etc).

  • The World Health Organisation has classed any form of night-time shift work as a probable carcinogen

  • After just one night of only four or five hours of sleep, your natural killer cells – the ones that attack the cancer cells that appear in your body every day – drop by 70%.
  • It is proven that some people perform better in evenings or mornings. Find out who you are, and utilise this knowledge to your advantage
  • Cut down on blue light before sleep. If you must use a screen moments before bedtime, try to turn on night shift or any other screen mode that eliminates as much blue light as possible
  • Caffeine can affect our brains much longer than most of us realise. If you have some coffee at 12 PM, a quarter of that caffeine will be still be active in your brain around midnight. It takes roughly 5-7 hours for the amount of caffeine in your body to halve.
  • Adults above 45 years old who sleep less than 6 hours per night are 200% more likely to suffer a stroke or heart attack throughout their life compared to people who hit 8 hours a night
  • The shorter you sleep every night, the shorter your lifespan.
  • Sleep is a crucial factor in increasing skill level for anything in life. Most of the programming in your brain happens not during practice, but while sleeping.
  • Being awake for 16 hours will result in the brain starting to depreciate in cognitive functioning. Try and be aware of your own limitations and brief others accordingly!

Aviation resources for managing sleep and fatigue

Please find my personal list of aviation sources that provide excellent material on fatigue, sleep, and safety statistics.

ICAO Doc 9966: Manual for the Oversight of Fatigue Management Approaches

Aircrew Fatigue: A Review of Research Undertaken on Behalf of the UK Civil Aviation Authority

EUROCONTROL Fatigue and Sleep Management Booklet

FAA Advisory Circular 120-100: Basics of Aviation Fatigue

EASA’s Scientific and Medical Evaluation of Flight Time Limitations

Independent research on Pilot Fatigue Measurement by the Netherlands Aerospace Centre


Sleep is crucial for all of us. You wouldn’t step in a car or plane while being under the influence or alcohol. The same counts for being sleepy or fatigued: you shouldn’t be in positions where safety is on the line, if you’re not taking your sleep and risk of fatigue seriously.

Sleep isn’t straight forward for a lot of people though, so try to use the variables that you do have control over to your advantage to maximise your chances of getting an adequate amount every day and while working through nights.

Categories: Guides

Jop Dingemans

AW169 HEMS Commander | Founder of Pilots Who Ask Why | Aerospace Engineer | Former Flight Instructor


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