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Many different illusions can be experienced in flight; some can lead to spatial
disorientation while others can lead to landing errors. Illusions rank among the most
common factors cited as contributing to fatal accidents.
Illusions Leading to Spatial Disorientation
Various complex motions and forces and certain visual scenes encountered in flight
can create illusions of motion and position. Spatial disorientation from these
illusions can be prevented only by visual reference to reliable, fixed points on
the ground or to flight instruments. For more information on the illusions such as:
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Coriolis illusion
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Graveyard spiral
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Somatogravic illusion
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False horizon
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Autokinesis
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Elevator illusion
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Inversion illusion
Refer to Chapter 8 of the Aeronautical Information Manual (AIM).
Illusions Leading to Landing Errors
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 and by using
an electronic glide slope or VASI system when available. The most common illusions leading
to landing errors are:
- Runway width illusion. A narrower than 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 likely fly a lower approach, with the risk of striking
objects along the approach path or landing short. A wider than usual runway can have the
opposite effect, with the risk of overshooting the runway.
- Runway and terrain slopes illusion. An up-sloping runway, up-sloping terrain,
or both, can create the illusion that the aircraft is at a higher altitude than it is
actually is. The pilot who does not recognize this illusion will actually fly a lower
than normal approach. A down-sloping runway, down-sloping approach terrain, or both, can
have the opposite effect.
- 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 attitude than it actually is. The pilot who does not
recognize this illusion will fly a lower approach.
- Atmospheric illusions. Rain on the windscreen can create the illusion of
greater height, and atmospheric haze can create the illusion of being at a greater
distance from the runway.
- Ground lighting illusions. Bright runway and approach light systems,
especially when few lights illuminate the surrounding terrain, may cause the illusion
of less distance from the runway. A pilot who does not recognize this will fly a
higher approach. Conversely, the pilot over-flying terrain which has few lights to
provide height cues may make a lower than normal approach.
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