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Flight Performance - Level 3

Human Factors-Section 1


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, and 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 pilot.

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 available.

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 tricks.

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 resources.

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.



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 canceling or postponing a flight.



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 center 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.

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 misinterpreted.

2.  ABOVE 10,000 FEET
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 discoloring 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 lost.

At 18,000 feet, primary shock sets in and the individual loses consciousness.

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.


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.



The only way to prevent hypoxia is to take steps against it before its’ onset. Remember the rule: Oxygen above 10,000 feet by day and above 5,000 feet at night.

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Updated: March 12, 2004