Human Performance – Fatigue

What does fatigue mean to you?

ICAO Definition of Fatigue

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

ICAO October 2010 

Fatigue is a safety issue and is broadly defined as the result of inadequate rest over a period of time that leads to physical and mental impairment

Performance is reduced typically in one of 5 areas:

• Situational awareness
• Memory (particularly short term)
• Simulation ability (the ability to project current events to a future state)
• Performance insight (what is the aircraft presently doing vs what it should be doing, and Emotional control.

Where would you find …?

Now we consider fatigue and tiredness as part of the same continuum.

Where would the following terms be on the continuum:

• Weariness?
• Tiredness?
• Fatigue? (when ‘fatigue can impair (or has potential to impair) our ability to operate safely’?)

We all have different perceptions and might put these in a different order or at different points. It does not matter what terminology you use, we now define all of these terms as ‘fatigue’ if performance is reduced.

Consider where ‘Unfit for flying” due Fatigue fit on the continuum?

When we talk about fatigue, we are most concerned with the section of the continuum that affects our ability to operate safely and when we consider ourselves unfit for duty.

As with any type ‘Unfit for flying’ it is based on your own personal judgement.

In this module, we want to give you information to help you:

• Identify when fatigue is impacting your performance.
• Use strategies to manage your alertness levels to prevent it impacting your performance.
• Know what your responsibilities are if you consider yourself unfit for duty.

Some common causes of fatigue:

• Long hours of school
• Travel to / from school
• Lack of sleep
• Poor quality or disrupted sleep
• Stress
• Temperature extremes
• Sustained mental or physical effort
• Poor nutrition
• High concentration tasks
• Rapid or complex information processing
• Tasks requiring prolonged alertness

Different jobs have different reasons for becoming fatigued eg:

• Cabin Crew – Physical exertion, being on their feet for long periods of time.
• Flight Crew – Mental exertion, long periods of attention / concentration and complicated calculations and decisions (route planning).

Here are some possible indicators have you felt or seen in other crew that may indicate that they are fatigued:

• Lethargy, yawning, tiredness
• Limbs feel heavy
• Headaches or nausea
• Lack of response
• Difficulty remembering
• Head nodding
• Decreased perception of risk
• Micro sleeps
• Impaired decision making
• Irritability
• Delayed reaction time
• Apathy or indifference
• Easily distracted
• Lack of motivation
• Increase in errors

Sleep deprivation

Truck drivers who had been awake for 18-20 hours had a performance equivalent to 0.1% Blood Alcohol Concentration

  Australian Department of Infrastructure and Transport (2000)

Sleep deprivation can have a serious impact on our performance, similar to that of drinking alcohol. Fatigue affects individual is differently, some can perform at a higher level for longer than others, however in this study:

• Being awake for 17hrs had an equivalent performance as having a blood alcohol level of 0.05%
• Being awake for 20hrs had an equivalent performance as having a blood alcohol level of 0.1%

Source: Australian Department of Infrastructure and Transport (2000)

Note: while this study can tell us a lot about the potential impact of fatigue on performance, it is important to note that the operating conditions for truck drivers are quite different to our operations, in that they have fewer defences against fatigue e.g.:

• They work alone without a team to monitor performance or fatigue symptoms
• They have less strict SOPs, and in this particular study they were not given any rest opportunities.

A state of partial or full unconsciousness

during which voluntary functions are suspended and the body rests and restores itself.

It is of great importance to understand that sleep is a way for pilots to manage fatigue. In fact, the only way of recovering from fatigue is through sleep!

It is your responsibility to ensure that you have had sufficient rest prior to flying. –

While we can function on less than our normal amounts of sleep for a couple of nights, when sleep debt accumulates performance is degraded.

Why do we need sleep?

• Sleep is a physiological need like thirst or hunger.
• It is our body’s way of cleaning and maintaining our brain cells, this occurs as the fluid is filtered as we sleep.
• It has been associated with healing and building our immune systems, memory consolidation, and growth. 
• Extreme sleep deprivation can result in hallucination and, in extreme cases, death.

What events in your personal life affect your ability to get a decent amount of good quality sleep?

Work out what sleep amount is right for you (everybody is different):

• Typical adult is 8 hours sleep per night so take 8 hours x by 7= 56
• Less actual sleep over the week 6 + 8 + 9 + 7 + 8 + 7.5 + 6.5 = 52
• Therefore in this situation there is a 4 hour sleep debt

CASE STUDY: The Impact of Sleep Deprivation

• In 1959, Peter Tripp, a 32 year old New York DJ stayed awake for 201 hours (about 8 days) as a stunt for charity. After 48 hours he started having visual hallucinations (he saw cobwebs in his shoes).
• After 100 hours he had extreme difficulty with cognitive tests and he thought a tweed suit worn by one of the scientists observing him was a suit of fuzzy worms.
• By 170 hours he was unsure of who he was and required frequent proof of identity.
• After 200 hours he thought he was the victim of conspiracy among the doctors and researchers observing him.
• After the stunt, Tripp slept for 13 hours and 13 minutes spending the majority of this time in REM sleep. Initially they said that he made a full recovery, however Peter Tripp experienced brain damage, which lead to him losing his job and ultimately his marriage also broke down.
• The word ‘Tripping’ is believed to have come from Peter Tripps fatigued behaviour.

• Sleep needs vary from person to person, and they change throughout the lifecycle. (As shown on the screen)
• Most people fall asleep naturally somewhere between 10 p.m. and 7 a.m. Sleeping outside these times is more difficult, more broken.
• Some research suggests that nightshift workers get one to three hours less sleep per day than dayshift workers. In addition to sleeping less, people who work shifts often get sleep of a lower quality.
• Note: the need for sleep is not correlated with adult age. However aged people achieve lower quality sleep, therefore desire more hours of it.

When we sleep, our bodies don’t just switch off, they cycle through different stages of light and deep sleep. Each stage is identifiable by distinctive brain wave patterns. The various sleep stages follow each other in a continuous cycle that lasts between 90 and 120 minutes.

Each cycle is composed of five sleep stages:

• Stage 1 – Falling asleep
• Stage 2 – Light sleep
• Stages 3 and 4 – Deep sleep stages where the body regenerates physically.
• REM (rapid eye movement) sleep – This is the stage of sleep when we dream.
• REM is not a “stage”. It’s qualitatively different. We usually enter REM from stages 1-2.

Average amount of sleep required is 6 to 8 hours in 24, Therefore, when is the best time to sleep?

Circadian rhythms are the physical, mental and behavioural changes that follow roughly a 24 hour cycle.

• Cues like sunlight and darkness keep the rhythm to the 24 hour cycle of each day.
• Note: Other cues like mealtimes and outside temperature can also affect our circadian rhythm.

Our individual performance also follows this rhythm;

• We perform best at about 1pm and
• Relatively poorly at 3-4am in the morning, when our body wants us to sleep.

Any team that operates through the night, need to be aware of fatigue signs and symptoms at circadian low points and manage them accordingly. eg protective behaviour, double checking ourselves, looking after our team, using checklists, giving ourselves time to make good decisions.

We can use our knowledge of circadian rhythm to manage our fatigue and plan for rest periods, e.g.:

• if you have work that starts late, you may be working through a circadian low and should be extra vigilant and look out for fatigue signs and symptoms
• If you arrive home in the morning after a work shift it will be difficult to sleep because of a circadian high so you may need to plan an extra nap in the afternoon

Some ideas to help prepare yourself for sleep:

• Avoid anxiety
• Consider when to eat and drink
• Avoid blue light
• Establish a bedtime routine
• Take a warm shower

As Crew, we need to be particularly aware of fatigue signs and symptoms at our circadian low points and manage them accordingly. eg protective behaviour, double checking ourselves, looking after our team, using checklists, giving ourselves time to make good decisions. 

We can use our knowledge of circadian rhythm to manage our fatigue and plan for rest periods, e.g.:

• If you have a flight that starts late, you may be working through a circadian low and should be extra vigilant and look out for fatigue signs and symptoms
• If you arrive home in the morning it will be difficult to sleep because of a circadian high so you may need to plan an extra nap in the afternoon

What sort of other strategies may also be effective?

• Balanced diet with good nutrition
• Exercise regularly (not before rest periods)
• Appropriate use of Caffeine (excess use may result in less effectiveness)

What sort of activities should be avoided?

• Excess alcohol consumption
• Alcohol reduces the time it takes to fall asleep but also disrupts sleep, reduces REM sleep.
• Exercising just before rest periods
• Taking medication without consulting your doctor