Elsewhere we have discussed the technical aspects of
flying. The reader should now understand how lift is produced by an airfoil to
make an airplane fly, the basic construction of an airframe. ail about the
operation and care of an aero engine, how to use aircraft communication and
navigation radio equipment, how to navigate from A to B, the vagaries of
weather, etc. Not too many years ago, it was generally believed that if an
individual had a good understanding of all these technical aspects of pilotage,
he had acquired the basic prerequisites to be a successful, efficient and safe
In the last few years, however, it has been learned that a thorough grasp of
these subjects, though essential, is not enough. Human factors are a very
important part of flight crew training. Human aspects, such as cockpit
organization, crew co-ordination, fitness and health, sensory illusions and
decision making are as vital to safety in the air as are flying techniques. The
relationship of people with machines, the environment and other people is part
of the human factor equation.
There is much to understand about the pilot himself and his physical and
involuntary reactions to the unnatural environmental conditions of flying.
During the Second World War, it was first realized that some airplane losses
were due to pilot incapacitation rather than to enemy action. The challenge of
explaining these unusual occurrences was taken up and since that time much
research has been conducted into such subjects as hypoxia, spatial
disorientation, hyperventilation, the bends, impairment due to drugs and
alcohol, and mental stress. Startling and sobering information is now
Man is essentially a terrestrial creature. His body is equipped to operate at
greatest efficiency within relatively narrow limits of atmospheric pressure and,
through years of habit, has adapted itself to movement on the ground.
In his quest for adventure and his desire for progress, man has ventured into
a foreign environment, the air high above the ground. But these lofty heights
are not natural to man. As altitude increases, the body becomes less and less
efficient to a point, at sufficient altitude, of incapacitation and
unconsciousness. Completely deprived of oxygen, the body dies in 8 minutes.
Without ground reference, the senses can play tricks, sometimes fatal
Airplane accidents are an occurrence that every conscientious pilot is
concerned with preventing. Most aircraft accidents are highly preventable. Many
of them have one factor in common. They are precipitated by some human failing
rather than by a mechanical malfunction. In fact, statistics indicate that human
factors are involved in 85% of aircraft accidents. Many of these have been the
result of disorientation, physical incapacitation and even the death of the
pilot during the flight. Others are the result of poor management of cockpit
It is the intention of this chapter to explain briefly some of these human
factors, to help pilots understand and appreciate the capacities and limitations
of their own bodies, so that flying might never be a frightening or dangerous
undertaking. But instead, the enjoyable and safe and efficient experience ail
lovers of airplanes and the airways have always believed it to be.
B. general health
Since flying an airplane demands that the pilot be alert and in full command
of his abilities and reasoning, it is only common sense to expect that. an
individual will ensure that he is free of any conditions that would be
detrimental to his alertness, his ability to make correct decisions, and his
rapid reaction times before seating himself behind the wheel of an airplane.
Certain physical conditions such as serious heart trouble, epilepsy,
uncontrolled diabetes, and other medical problems that might cause sudden
incapacitation and serious forms of psychiatric illness associated with loss of
insight or contact with reality may preclude an individual from being judged
medically fit to apply for a license.
Other problems such as acute infections are temporarily disqualifying and
will not affect the status of a pilot's license. But they will affect his
immediate ability to fly, and he should seek his doctor's advice before
returning to the cockpit of his airplane.
In fact, any general discomfort, whether due to colds, indigestion, nausea,
worry, lack of sleep or any other bodily weakness, is not conducive to safe
flying. Excessive fatigue is perhaps the most insidious of these conditions,
resulting in inattentiveness, slow reactions and confused mental processes.
Excessive fatigue should be considered a reason for cancelling or postponing a
The advance in aeronautical engineering during the past few years has
produced more versatile airplanes capable of flying at much higher altitudes
than only a few years ago were considered attainable by the private pilot. At
such high altitudes, man is susceptible to one of the most insidious
physiological problems. hypoxia. Because hypoxia comes on without warning
of any kind, the general rule of oxygen above 10,000 feet ASL by day and above
5000 feet ASL by night is one the wise pilot will practice to avoid the hazard
of this debilitating condition. Hypoxia can be defined as a lack of sufficient
oxygen in the body cells or tissues.
The greatest concentration of air molecules is near to the earth's surface.
There is progressively less air and therefore less oxygen (per unit volume) as
you ascend to higher altitudes. Therefore each breath of air that you breathe
at, for example, 15,000 feet ASL has about half the amount of oxygen of a breath
taken at sea level.
The most important fact to remember about hypoxia is that the individual is
unaware that he is exhibiting symptoms of this condition. The brain centre that
would warn him of decreasing efficiency is the first to be affected and the
pilot enjoys a misguided sense of well-being. Neither is there any pain, or any
other warning signs that tell him that his alertness is deteriorating. The
effects of hypoxia progress from euphoria (feeling of well being) to reduced
vision, confusion, inability to concentrate, impaired judgment, slowed reflexes
to eventual loss of consciousness.
effects on visions at 5000 feet
The retina of the eye is
actually an outcropping of the brain and as such is more dependent on an
adequate supply of oxygen than any other part of the body. For this reason, the
first evidence of hypoxia occurs at 5000 feet in the form of diminished night
vision. Instruments and maps are misread; dimly lit ground features are
It is true that general physical fitness has
some bearing on the exact altitude at which the effects of hypoxia will first
affect a particular individual. Age, drinking habits, use of drugs, lack of
rest, etc.. all increase the susceptibility of the body to this condition.
However, the average has been determined at 10,000 feet.
At 10,000 feet, there is a definite but undetectable hypoxia. This altitude
is the highest level at which a pilot should consider himself efficient in
judgment and ability. However, continuous operation even at this altitude for
periods of more than, say, four hours can produce fatigue because of the reduced
oxygen supply and a pilot should expect deterioration in concentration, problem
solving and efficiency.
At 14,000 feet, lassitude and indifference are appreciable. There is dimming
of vision, tremor of hands, clouding of thought and memory and errors in
judgment. Cyanosis (blue discolouring of the fingernails) is first noticed.
At 16,000 feet, a pilot becomes disoriented, is belligerent or euphoric and
completely lacking in rational judgment. Control of the airplane can be easily
At 18,000 feet, primary shock sets in and the individual loses
At higher altitudes, death may result after a prolonged period.
The Air Navigation Orders rule that an aircraft should not be operated for
more than 30 minutes between 10,000 feet and 13,000 feet or at ail above 13,000
feet unless oxygen is readily available for each crew member.
D. stagnant hypoxia
Stagnant hypoxia is a condition in which there is a temporary displacement of
blood in the head. It occurs as a result of positive "g" forces (as in an abrupt
pull out from a high speed dive), and, can be attributed to the fact that the
circulatory system is unable to keep blood pumped to, the head.
E. prevention of hypoxia
The only way to prevent hypoxia is to take steps against it before itsí
onset. Remember the rule: Oxygen above 10,000 feet by day and above 5,000 feet