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will appear to move about when stared at for many
seconds. The disoriented pilot will lose control of the
aircraft in attempting to align it with the light.
3. Illusions Leading to Landing Errors.
(a) Various surface features and atmospheric
conditions encountered in landing can create illusions
of incorrect height above and distance from the
runway threshold. Landing errors from these
illusions can be prevented by anticipating them
during approaches, aerial visual inspection of
unfamiliar airports before landing, using electronic
glide slope or VASI systems when available, and
maintaining optimum proficiency in landing
procedures.
(b) Runway width illusion. A narrowerthan‐
usual runway can create the illusion that the
aircraft is at a higher altitude than it actually is. The
pilot who does not recognize this illusion will fly a
lower approach, with the risk of striking objects along
the approach path or landing short. A wider‐thanusual
runway can have the opposite effect, with the
risk of leveling out high and landing hard or
overshooting the runway.
(c) Runway and terrain slopes illusion. An
upsloping runway, upsloping terrain, or both, can
create the illusion that the aircraft is at a higher
altitude than it actually is. The pilot who does not
recognize this illusion will fly a lower approach. A
downsloping runway, downsloping approach terrain,
or both, can have the opposite effect.
(d) Featureless terrain illusion. An
absence of ground features, as when landing over
water, darkened areas, and terrain made featureless
by snow, can create the illusion that the aircraft is at
a higher altitude than it actually is. The pilot who does
not recognize this illusion will fly a lower approach.
(e) Atmospheric illusions. Rain on the
windscreen can create the illusion of greater height,
and atmospheric haze the illusion of being at a greater
distance from the runway. The pilot who does not
recognize these illusions will fly a lower approach.
Penetration of fog can create the illusion of pitching
up. The pilot who does not recognize this illusion will
steepen the approach, often quite abruptly.
(f) Ground lighting illusions. Lights along
a straight path, such as a road, and even lights on
moving trains can be mistaken for runway and
approach lights. Bright runway and approach lighting
systems, especially where few lights illuminate the
surrounding terrain, may create the illusion of less
distance to the runway. The pilot who does not
recognize this illusion will fly a higher approach.
Conversely, the pilot overflying terrain which has few
lights to provide height cues may make a lower than
normal approach.
8-1-6. Vision in Flight
a. Introduction. Of the body senses, vision is the
most important for safe flight. Major factors that
determine how effectively vision can be used are the
level of illumination and the technique of scanning
the sky for other aircraft.
b. Vision Under Dim and Bright Illumination.
1. Under conditions of dim illumination, small
print and colors on aeronautical charts and aircraft
instruments become unreadable unless adequate
cockpit lighting is available. Moreover, another
aircraft must be much closer to be seen unless its
navigation lights are on.
2. In darkness, vision becomes more sensitive to
light, a process called dark adaptation. Although
exposure to total darkness for at least 30 minutes is
required for complete dark adaptation, a pilot can
achieve a moderate degree of dark adaptation within
20 minutes under dim red cockpit lighting. Since red
light severely distorts colors, especially on aeronautical
charts, and can cause serious difficulty in focusing
the eyes on objects inside the aircraft, its use is
advisable only where optimum outside night vision
capability is necessary. Even so, white cockpit
lighting must be available when needed for map and
instrument reading, especially under IFR conditions.
Dark adaptation is impaired by exposure to cabin
pressure altitudes above 5,000 feet, carbon monoxide
inhaled in smoking and from exhaust fumes,
deficiency of Vitamin A in the diet, and by prolonged
exposure to bright sunlight. Since any degree of dark
adaptation is lost within a few seconds of viewing a
2/14/08 AIM
Fitness for Flight 8-1-7
bright light, a pilot should close one eye when using
a light to preserve some degree of night vision.
3. Excessive illumination, especially from light
reflected off the canopy, surfaces inside the aircraft,
clouds, water, snow, and desert terrain, can produce
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