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85 percent of visible light (15 percent transmittance)
and all colors equally (neutral transmittance), with
negligible image distortion from refractive and
prismatic errors.
c. Scanning for Other Aircraft.
1. Scanning the sky for other aircraft is a key
factor in collision avoidance. It should be used
continuously by the pilot and copilot (or right seat
passenger) to cover all areas of the sky visible from
the cockpit. Although pilots must meet specific visual
acuity requirements, the ability to read an eye chart
does not ensure that one will be able to efficiently spot
other aircraft. Pilots must develop an effective
scanning technique which maximizes one’s visual
capabilities. The probability of spotting a potential
collision threat obviously increases with the time
spent looking outside the cockpit. Thus, one must use
timesharing techniques to efficiently scan the
surrounding airspace while monitoring instruments
as well.
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 7/10 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 1/4 to 1/3 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 “emptyfield
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.
8−1−7. 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
AIM 2/19/04
8−1−8 Fitness for Flight
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
　
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