AIM 

4/20/23

 

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Fitness for Flight

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