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Iris
The pupil (aperture) is the opening at
the center of the iris. The size of the
pupil is adjusted to control the amount
of light entering the eye.
Pupil
Light passes through the cornea (the
transparent window on the front of the
eye) and then through the lens to
focus on the retina.
Cornea
Rod concentration
After the eyes have adapted to the dark, the entire process
is reversed when entering a lighted room. The eyes are fi rst
dazzled by the brightness, but become completely adjusted
in a few seconds, thereby losing their adaptation to the dark.
Now, if the dark room is reentered, the eyes again go through
the long process of adapting to the darkness.
Before and during night fl ight, the pilot must consider the
adaptation process of the eyes. First, the eyes should be
allowed to adapt to the low level of light. Then, the pilot
should avoid exposing them to any bright white light that
would cause temporary blindness and possibly result in
serious consequences.
Temporary blindness, caused by an unusually bright light,
may result in illusions or afterimages until the eyes recover
from the brightness. The brain creates these illusions
reported by the eyes. This results in misjudging or incorrectly
identifying objects, such as mistaking slanted clouds for the
horizon or a populated area for a landing fi eld. Vertigo is
experienced as a feeling of dizziness and imbalance that can
create or increase illusions. The illusions seem very real and
pilots at every level of experience and skill can be affected.
Recognizing that the brain and eyes can play tricks in this
manner is the best protection for fl ying at night.
Good eyesight depends upon physical condition. Fatigue,
colds, vitamin defi ciency, alcohol, stimulants, smoking, or
medication can seriously impair vision. Keeping these facts
in mind and taking appropriate precautions should help
safeguard night vision.
12-7
Figure 12-7. At night, the horizon may be hard to discern due to dark
terrain and misleading light patterns on the ground.
In addition to the principles previously discussed, the following
actions aid in increasing night vision effectiveness:
• Adapt the eyes to darkness prior to fl ight, and keep
them adapted. About 30 minutes is needed to adjust
the eyes to maximum effi ciency after exposure to a
bright light.
• Use oxygen during night fl ying, if available. Keep in
mind that a signifi cant deterioration in night vision
can occur at altitudes as low as 5,000 feet.
• Close one eye when exposed to bright light to help
avoid the blinding effect.
• Avoid wearing sunglasses after sunset.
• Move the eyes more slowly than in daylight.
• Blink the eyes if vision becomes blurred.
• Concentrate on seeing objects.
• Force the eyes to view off center.
• Maintain good physical condition.
• Avoid smoking, drinking, and using drugs that may
be harmful.
Unique WSC Flight Characteristics
If the WSC aircraft is trimmed properly and the pilot is
profi cient in the basic fl ight maneuvers of climbs, cruise,
and descent procedures, the WSC aircraft speed is easily
determined with control bar pressure and position for normal
fl ight conditions. A pilot can also determine basic climbs and
descents through the feel of the aircraft with the airspeed and
throttle positions. Therefore, basic pitch control can be done
by a profi cient pilot with his or her eyes closed.
As discussed in Chapter 2, Aerodynamics, WSC aircraft
are generally not designed to be roll stable, and any engine
turning effect or movement of the air can put the WSC aircraft
into a roll, which it maintains unless corrected by the pilot.
In other words, releasing the control bar in a WSC aircraft
will not level a bank back to straight fl ight. The pilot must
continually provide input to fl y a constant heading even if this
control is small corrections. In other words, the pilot cannot
level the wings or fl y a straight heading for very long with
his or her eyes closed.
To maintain a constant heading or ground track, one of
three instruments can be used: magnetic compass, global
positioning system (GPS), and aircraft heading indicator.
Without a visual reference, these can be used to fl y straight.
An attitude indicator can be used on WSC aircraft providing
additional instrument reference. These instruments and others
are discussed later in this chapter.
Night Illusions
In addition to night vision limitations, pilots should be aware
that night illusions could cause confusion and concerns
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Weight-Shift Control Aircraft Flying Handbook(137)
