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• 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 illness.
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 dizziness.
16-13
T
ype Beverage Typical Serving Pure Alcohol (oz) Content (oz)Table WineLight BeerAperitif LiquorChampagneVodkaWhiskey 4.0 12.0 1.5 4.0 1.0 1.25.48.48.38.48.50.50 0.01–0.05 average individual appears normal (10–50 mg%) 0.03–0.12* mild euphoria, talkativeness, decreased (30–120 mg%) inhibitions, decreased attention, impaired judgment, increased reaction time 0.09–0.25 emotional instability, loss of critical (90–250 mg%) judgment, impairment of memory and comprehension, decreased sensory response, mild muscular incoordination 0.18–0.30 confusion, dizziness, exaggerated (180–300 mg%) emotions (anger, fear, grief) impaired visual perception, decreased pain sensation, impaired balance, staggering gait, slurred speech, moderate muscular incoordination 0.27–0.40 apathy, impaired consciousness, stupor,(270–400 mg%) significantly decreased response to stimulation, severe muscular incoordination, inability to stand or walk, vomiting, incontinence of urine and feces 0.35–0.50 unconsciousness, depressed or (350–500 mg%) abolished reflexes, abnormal body temperature, coma; possible death from respiratory paralysis (450 mg% or above)* Legal limit for motor vehicle operation in most states is 0.08 or 0.10% (80–100 mg of alcohol per dL of blood).
Figure 16-8. Impairement scale with alcohol use.
The first noticeable effect of dehydration is fatigue, which in turn makes top physical and mental performance difficult, if not impossible. Flying for long periods in hot summer temperatures or at high altitudes increases the susceptibility to dehydration because these conditions tend to increase the rate of water loss from the body.
To help prevent dehydration, drink two to four quarts of water every 24 hours. Since each person is physiologically different, this is only a guide. Most people are aware of the eight-glasses-a-day guide: If each glass of water is eight ounces, this equates to 64 ounces, which is two quarts. If this fluid is not replaced, fatigue progresses to dizziness, weakness, nausea, tingling of hands and feet, abdominal cramps, and extreme thirst.
The key for pilots is to be continually aware of their condition. Most people become thirsty with a 1.5 quart deficit, or a loss of 2 percent of total body weight. This level of dehydration triggers the “thirst mechanism.” The problem is that the thirst mechanism arrives too late and is turned off too easily. A small amount of fluid in the mouth will turn this mechanism off and the replacement of needed body fluid is delayed.
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Pilot's Handbook of Aeronautical Knowledge航空知识手册3(48)
