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Pilot's Handbook of Aeronautical Knowledge
Aeromedical Factors

Health and Physiological Factors Affecting Pilot Performance

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Stress falls into two broad categories, acute (short term) and
chronic (long term). Acute stress involves an immediate
threat that is perceived as danger. This is the type of stress that
triggers a "flight or flight" response in an individual, whether
the threat is real or imagined. Normally, a healthy person can
cope with acute stress and prevent stress overload. However,
ongoing acute stress can develop into chronic stress.
Chronic stress can be defined as a level of stress that presents
an intolerable burden, exceeds the ability of an individual
to cope, and causes individual performance to fall sharply.

Unrelenting psychological pressures, such as loneliness,
financial worries, and relationship or work problems can
produce a cumulative level of stress that exceeds a person's
ability to cope with the situation. When stress reaches these
levels, performance falls off rapidly. Pilots experiencing
this level of stress are not safe and should not exercise their
airman privileges. Pilots who suspect they are suffering from
chronic stress should consult a physician.

Fatigue is frequently associated with pilot error. Some of
the effects of fatigue include degradation of attention and
concentration, impaired coordination, and decreased ability
to communicate. These factors seriously influence the
ability to make effective decisions. Physical fatigue results
from sleep loss, exercise, or physical work. Factors such as
stress and prolonged performance of cognitive work result
in mental fatigue.

Like stress, fatigue falls into two broad categories: acute
and chronic. Acute fatigue is short term and is a normal
occurrence in everyday living. It is the kind of tiredness
people feel after a period of strenuous effort, excitement, or
lack of sleep. Rest after exertion and 8 hours of sound sleep
ordinarily cures this condition.

A special type of acute fatigue is skill fatigue. This type of
fatigue has two main effects on performance:
• Timing disruption—Appearing to perform a task as
usual, but the timing of each component is slightly off.
This makes the pattern of the operation less smooth,
because the pilot performs each component as though it
were separate, instead of part of an integrated activity.
• Disruption of the perceptual field—Concentrating
attention upon movements or objects in the center of
vision and neglecting those in the periphery. This is
accompanied by loss of accuracy and smoothness in
control movements.

Acute fatigue has many causes, but the following are among
the most important for the pilot:
• Mild hypoxia (oxygen deficiency)
• Physical stress
• Psychological stress and
• Depletion of physical energy resulting from
psychological stress
• Sustained psychological stress

Sustained psychological stress accelerates the glandular
secretions that prepare the body for quick reactions during
an emergency. These secretions make the circulatory and
respiratory systems work harder, and the liver releases energy
to provide the extra fuel needed for brain and muscle work.
When this reserve energy supply is depleted, the body lapses
into generalized and severe fatigue.

Acute fatigue can be prevented by proper diet and adequate
rest and sleep. A well-balanced diet prevents the body from
needing to consume its own tissues as an energy source.
Adequate rest maintains the body's store of vital energy.
Chronic fatigue, extending over a long period of time, usually
has psychological roots, although an underlying disease is
sometimes responsible. Continuous high stress levels produce
chronic fatigue. Chronic fatigue is not relieved by proper diet
and adequate rest and sleep, and usually requires treatment
by a physician. An individual may experience this condition
in the form of weakness, tiredness, palpitations of the heart,
breathlessness, headaches, or irritability. Sometimes chronic
fatigue even creates stomach or intestinal problems and
generalized aches and pains throughout the body. When the
condition becomes serious enough, it leads to emotional

If suffering from acute fatigue, stay on the ground. If fatigue
occurs in the flight deck, no amount of training or experience
can overcome the detrimental effects. Getting adequate rest
is the only way to prevent fatigue from occurring. Avoid
flying without a full night's rest, after working excessive
hours, or after an especially exhausting or stressful day. Pilots
who suspect they are suffering from chronic fatigue should
consult a physician.

Dehydration and Heatstroke
Dehydration is the term given to a critical loss of water from
the body. Causes of dehydration are hot flight decks and
flight lines, wind, humidity, and diuretic drinks—coffee, tea,
alcohol, and caffeinated soft drinks. Some common signs of
dehydration are headache, fatigue, cramps, sleepiness, and