AIM 

4/20/23 

2. 

While the eyes can observe an approximate 200 degree arc of the horizon at one glance, only a very small 

center area called the fovea, in the rear of the eye, has the ability to send clear, sharply focused messages to the 

brain. All other visual information that is not processed directly through the fovea will be of less detail. An 

aircraft at a distance of 7 miles which appears in sharp focus within the foveal center of vision would have to 

be as close as 

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 of a mile in order to be recognized if it were outside of foveal vision. Because the eyes can 

focus only on this narrow viewing area, effective scanning is accomplished with a series of short, regularly 

spaced eye movements that bring successive areas of the sky into the central visual field. Each movement should 

not exceed 10 degrees, and each area should be observed for at least 1 second to enable detection. Although 

horizontal back-and-forth eye movements seem preferred by most pilots, each pilot should develop a scanning 

pattern that is most comfortable and then adhere to it to assure optimum scanning. 

3. 

Studies show that the time a pilot spends on visual tasks inside the cabin should represent no more that 

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 of the scan time outside, or no more than 4 to 5 seconds on the instrument panel for every 16 seconds 

outside. Since the brain is already trained to process sight information that is presented from left to right, one 

may find it easier to start scanning over the left shoulder and proceed across the windshield to the right. 

4. 

Pilots should realize that their eyes may require several seconds to refocus when switching views 

between items in the cockpit and distant objects. The eyes will also tire more quickly when forced to adjust to 

distances immediately after close-up focus, as required for scanning the instrument panel. Eye fatigue can be 

reduced by looking from the instrument panel to the left wing past the wing tip to the center of the first scan 

quadrant when beginning the exterior scan. After having scanned from left to right, allow the eyes to return to 

the cabin along the right wing from its tip inward. Once back inside, one should automatically commence the 

panel scan. 

5. 

Effective scanning also helps avoid “empty-field myopia.” This condition usually occurs when flying 

above the clouds or in a haze layer that provides nothing specific to focus on outside the aircraft. This causes the 

eyes to relax and seek a comfortable focal distance which may range from 10 to 30 feet. For the pilot, this means 

looking without seeing, which is dangerous. 

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7.  Aerobatic Flight 

a. 

Pilots planning to engage in aerobatics should be aware of the physiological stresses associated with 

accelerative forces during aerobatic maneuvers. Many prospective aerobatic trainees enthusiastically enter 

aerobatic instruction but find their first experiences with G forces to be unanticipated and very uncomfortable. 

To minimize or avoid potential adverse effects, the aerobatic instructor and trainee must have a basic 

understanding of the physiology of G force adaptation. 

b. 

Forces experienced with a rapid push-over maneuver result in the blood and body organs being displaced 

toward the head. Depending on forces involved and individual tolerance, a pilot may experience discomfort, 

headache, “red-out,” and even unconsciousness. 

c. 

Forces experienced with a rapid pull-up maneuver result in the blood and body organ displacement toward 

the lower part of the body away from the head. Since the brain requires continuous blood circulation for an 

adequate oxygen supply, there is a physiologic limit to the time the pilot can tolerate higher forces before losing 

consciousness. As the blood circulation to the brain decreases as a result of forces involved, a pilot will 

experience “narrowing” of visual fields, “gray-out,” “black-out,” and unconsciousness. Even a brief loss of 

consciousness in a maneuver can lead to improper control movement causing structural failure of the aircraft or 

collision with another object or terrain. 

d. 

In steep turns, the centrifugal forces tend to push the pilot into the seat, thereby resulting in blood and body 

organ displacement toward the lower part of the body as in the case of rapid pull-up maneuvers and with the same 

physiologic effects and symptoms. 

e. 

Physiologically, humans progressively adapt to imposed strains and stress, and with practice, any maneuver 

will have decreasing effect. Tolerance to G forces is dependent on human physiology and the individual pilot. 

These factors include the skeletal anatomy, the cardiovascular architecture, the nervous system, the quality of 

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Fitness for Flight