How does fatigue affect aviation safety?


Fatigue human factors


Fatigue is human factors hazard because it affects most aspects of a person's ability to do their job and leads to human factors errors. In human factors, fatigue is one of many individual factors considered a cause of human error such as stress, personal events, etc.

Fatigue isn’t just a human factor hazard for the aviation industry only. It’s a hazard for all industries such as healthcare, construction, etc.


Do you know what I mean by Hazard?

A hazard is a condition or an object with the potential to cause or contribute to an incident or accident.


What is fatigue?

Fatigue means 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).

We understand from this definition that fatigue can reduce a person’s alertness and ability to safely perform safety-related operational duties.


In this article, I will further your knowledge about fatigue to help you to minimize its impact. Furthermore, you will understand how it reduces a person's mental or physical performance capability.


Fatigue is a Hazard

In 2003, during the holy month of Ramadan in Yemen (sleeping is after 5:30 a.m.), one of our loading workers was loading a Yemen Airways aircraft - a narrow body - which was prepared for a scheduled flight.

A worker loaded the passengers' luggage in the forward cargo hold, and as a result of waiting to load the rest of the luggage, he slept in the cargo hold.


His colleagues did not notice that he was sleeping in the cargo hold, and the cargo hold door was closed, and the aircraft took off.

About 25 minutes after take-off, the captain heard three knocks on the roof of the lower cargo compartment. So, the captain was surprised that the knocks were repeated in different numbers.

After evaluating the situation, the captain proceeded in the same way – knocks - with changing the number. Then, he waited for a while, he heard the same number of knocks from the cargo hold.

The captain made sure that there was a person inside the cargo hold. The captain returned to Sana'a Airport. While arriving, the door of the cargo hold was opened, and the worker safely got off.

I met this loading worker during my first job - as a secretary - in the security department of Yemen Airways, I asked him


How did that happen?

He replied laughing “I was tired, and I did not sleep well."

Do you agree with me that fatigue is a hazard?


Difference Between Tiredness and Fatigue

To differentiate between fatigue and tiredness, the tiredness that we feel is often alleviated through sleep and rest. While fatigue is an extension and continuation of tiredness without reducing it through sleep and rest.

So, tiredness is a symptom of fatigue.


Fatigue Types

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

(1) Transient fatigue is acute fatigue brought on by extreme sleep restriction or extended hours awake within 1 or 2 days.

(2) Cumulative fatigue is fatigue brought on by repeated mild sleep restriction or extended hours awake across a series of days.

(3) Circadian fatigue refers to reduced performance during nighttime hours, particularly during an individual’s “window of circadian low” (WOCL) (typically between 2:00 a.m. and 05:59 a.m.). [ref. FAA, AC no: 117-3]


Fatigue Symptoms

Fatigue can be mental or physical. Emotional fatigue also exists and affects mental and physical performance. I will list these fatigue symptoms:

A- Physical Symptoms

1)      Chronic tiredness or sleepiness

2)      Headache

3)      Dizziness

4)      Sore or aching muscles

5)      Muscle weakness

6)      Slowed reflexes and responses

7)      Impaired hand-to-eye coordination

8)      Appetite loss

9)      Reduced immune system function


B- Mental Symptoms

1)      Short-term memory problems

2)      Poor concentration

3)      Lapses of attention and vigilance

4)      Impaired logical reasoning and decision-making, including a reduced ability to assess [impaired decision-making and judgment].

5)      Delayed reactions (sometimes).

6)      Risk or appreciate consequences of actions.

7)      In some cases- hallucinations


C- Emotional Symptoms

1)      Moodiness, such as irritability

2)      Low motivation.

3)      Feeling of isolation

4)      Being annoyed


In addition, increased errors while performing tasks.


Common Causes of Fatigue

There is a wide range of causes that can trigger fatigue. Also, fatigue can be caused by several factors working in combination.

 I will categorize causes into four main factors:

1- Medical Causes

E.g., Illness, such as a thyroid disorder, heart disease, or diabetes.

Note. You should consult your doctor.

2- Lifestyle Causes

E.g., lack of sleep, individual factors, alcohol or drugs, etc.


3- Workplace Causes

E.g., workplace stress, shift work, poor workplace practices, etc.


4- Emotional Causes

E.g., mental health problems, such as stress, depression, and grief.


How to Manage fatigue

Each person first needs to understand the underlying causes of fatigue. Second, he is responsible for managing his fatigue levels. These are some tips for good fatigue management.


1- Sleep well

Improve your sleep, improve your life. Nine hours of sleep per night to recover from accumulated sleep debt.

2- Eat well

Eat regular meals.

3-Improve your lifestyle

Manage your daily activities and lifestyle to maximize rest.

4- Do Exercises

Do exercises regularly for more deep sleep.

5- Balance between family and work

Especially for those who are working on irregular schedules.

6- Report fatigue Issues

Help manage fatigue hazards.



Fatigue is a physiological state of reduced mental or physical performance capability. It reduces alertness and often reduces a person’s ability to focus and hold attention to the task being performed.

A fatigued person is easily distracted, less able to concentrate, forgets things, longer time to solve problems, has slow reaction times, etc.


Further reading :

1- ICAO Fatigue Management Guide for Airline Operators.

2- Basics of Aviation Fatigue, FAA, AC No: 120-100

3- ICAO doc 9966, Manual for the Oversight of Fatigue Management Approaches

Maged Saeed AL-Hadabi

Air Cargo / IATA Dangerous Goods | CGO, DGR, SMS Chief Instructor | Internal Auditor | DG Inspector linkedin

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