Acute fatigue occurs when a long period passes with a lack
of sleep. Chronic fatigue occurs when several acute fatigue periods
occur without adequate recovery time between. While some fatigue
is related to lack of sleep, not all is. Fatigue can result from
inadequate nutrition and over exertion. More information needs
to be obtained on fatigue distinguished from sleep as a factor
in accidents.
Some factors of physical condition are controllable and some
are not. Acute fatigue occurs when a long period passes with a
lack of sleep. Chronic fatigue occurs when several acute fatigue
periods occur without adequate recovery time between. Stress is
the result of events causing preoccupation, reducing external
awareness, and making activities subject to distraction. Stress
causes the taking of risks that would otherwise be unacceptable.
The mental/physical condition resulting from fatigue and stress
may cause the pilot to make unwise decisions.
There are many causes of fatigue: lack of sleep, hypoxia, noise,
time zone factors, temperature extremes, dehydration, stress and
more. When you are fatigued you are more irritable and easily
annoyed, you will suffer for lapses in short term memory, your
attention will fixate to the exclusion of all else, your performance
skills will decrease and you will be unaware of any impairment.
The causes of fatigue are primarily lack of recent sleep or
a chronic sleep deficiency. Additional fatigue arises from our
physiological reaction to noise and vibration, illness, hunger,
caffeine "down time", unresolved stress, hypoxia, dehydration,
errors in judgment and extended mental/physical demands.
What to Expect from Fatigue
Reduced vigilance
Increased temper excursions
Reduced ability to concentrate
Reduce awareness of deviations
Increased rationalization of errors
Increase in ‘know-better’ mistakes
Fatigue increases if you are "doing nothing"
Reduced comprehension of ATC instructions
Subtle Fatigue
This problem often begins with a distraction that causes fixation
on an instrument or occurrence. Complex flight operations are
the first skills to deteriorate.
Silence prevails
Seat posture relaxes
Bad judgment prevails
Instruments are ignored
Attention and vision fixates
Eye/hand skills begin to fail
Writing becomes less linear
Heading excursions take place
Movements decrease and slow
Clearances cannot be copied in total
Knowing where you are becomes a problem
Pilot accepts what exists as O.K. without checking
External references begin to fade from consciousness
Sleep
The most common cause of diminished alertness and proficiency
is lack of sleep. This condition is said to affect 30% of the
U.S. population. This may be due to an actual loss of sleep or
a change in a sleep pattern called the circadian rhythm. Pilots
tend to neglect their need for sleep. The need for sleep is a
defining limit to pilot mental capability. You must have sleep
or your mind will fail. Once beyond the limit pilot performance
deteriorates and can become irrational. Sleep is a restorative
and can be both stored and deprived within limits set by the biological
clock of the individual. As you grow older you will need less
sleep. Jet lag sleep patterns are worse when flying from west
to east. Accident rates climb precipitously when your body begins
demanding sleep. The average American gets about one hour too
little sleep each night.
Accident rates rise in the afternoon and become significant
at night. Postponing sleep causes a sleep deficit that as it increases
an accident becomes more likely. Jet lag is a type of sleep deficit.
A sleep deficit can best be resolved by going to bed early, not
by sleeping late. A large deficit cannot be made up in one night.
21% of aircraft accidents cite sleep deficiency as a factor.
When drowsiness occurs you cease to monitor the instruments.
You will tend to fixate and drift off mentally. We go into a mental
autopilot not thinking of what we are doing. This is the lowest
level of alertness. The next level of alertness is one in which
you are in constant search-and-scan, seeing what you are looking
at, hearing what is said and asking question. This is the flying"
mode from pre-flight to shutdown. This gradual deterioration of
alertness is best observed in watching others. It can creep up
on you and influence your flying without your even noticing. Your
alertness rises again when you have located a problem. You focus
on it and prepare to execute a solution. This might occur when
required to make a crosswind landing. The highest level of alertness
is when adrenaline begins to flow and survival becomes a factor.
Medicine
Any over-the-counter medication whose name ends in "ine"
should be checked in a flight medical examiner for use before
flying. Beware of any medicine that is supposed to make you feel
better. At altitude the effects may be damaging to flight safety.
Medicine taken is just as likely, even more likely, to be the
basis for grounding a pilot than is the ailment itself. Medicinal
side effects are both variable and unpredictable. Virtually all
medications have side effects. Never take a medication for the
first time and then fly. Make the safe decision if you are sick.
Carbon Monoxide
Is poisoning due to the exhaust fumes resulting from carbon
burning with insufficient oxygen to produce complete oxidation.
The resulting gas has one atom of carbon and one atom of oxygen.
CO is odorless, colorless and cannot be tasted. CO poisoning may
not be distinguished from fatigue or hypoxia except that the occurrence
can occur at any altitude. Engine exhaust in an aircraft has 7%
CO. Very small amounts of CO over a period of time will reduce
a pilot’s ability to fly safely. It is the length of exposure
as well as the amount that makes the critical difference. Susceptibility
to CO poisoning increases with altitude due to the propensity
of CO to enter blood. CO is 200 times more attracted to the blood
hemoglobin as is oxygen. As little as one part CO to 20,000 (.005%)
parts of air is enough to begin the death process of the brain.
Above 10% CO poisoning you will suffer from a headache. Above
20% you will be sleepy and sick to your stomach, HEADACHE, vision
and speech problems. You will be incapacitated above 40% and dead
at 70%. If you get a headache while flying, open the window and
shut off heater.
CO reduces ability of blood to carry oxygen. Symptoms are similar
to hypoxia. Headache, drowsiness, dizziness should initially be
corrected by opening outside air vents. CO has a half-life in
your body of about five hours. It will take a full day to recover.
70% of exhaust system failures result in CO poisoning. CO prevents
the hemoglobin from both carrying and releasing oxygen. Antihistamines,
alcohol, lack of sleep, or blood deficiency will exacerbate CO
poisoning. Prevention of CO poisoning is directly preventable
by proper aircraft maintenance. Club aircraft require extra alertness.
You might suspect CO exists in your cabin air as soon as you smell
some engine exhaust fumes.
Descend
Land ASAP
Use any oxygen
Shut off the heater
Get medical treatment
When in doubt, get on the ground.
Cold Weather
Hot or cold temperatures affect the quality of the preflight.
In the winter, as your body cools you tend to mentally and physically
slow down. Flying in an unheated aircraft in the winter will drastically
decrease your flying efficiency and effectiveness.
Last Modified January 28, ©2026 TAGE.COM
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