c. Upsloping Lane. The illusion that the runway is upsloping may make
the pilot perceive himself lower than normal due to a shorter relative
visual distance to a given touchdown point. This again may result in a
premature deceleration and pitch pull and a hard landing.
d. Downsloping Lane. The most crucial perception based on a visual
illusion is that of the downsloping runway. In this case the pilot would
perceive himself higher than normal, causing a late deceleration and pitch
pull which may result in hitting the tail stinger or tail boom.
4.
OTHER ILLUSIONS AND FLIGHT
There are also several visual illusions that may be present in flight
(especially during autorotational landings) that should be understood.
a. Sloping Threshold Terrain. The actual slope of the runway or the
terrain surrounding the runway may cause visual illusions that may create
problems for pilots.
(1) Upsloping runway: When making an approach to an upsloping
runway, a normal approach angle will appear too steep. Flying the approach
angle that appears normal could result in landing short of the desired
touchdown point.
(2) Downsloping runway: If an approach is being made to a
downsloping runway, a normal approach angle will appear to be too shallow.
Flying an apparent normal approach angle may cause the landing to be beyond
the desired touchdown point.
(3) Upsloping terrain: When the terrain surrounding the approach to
a runway is upsloping, the aircraft will appear to be above a normal
approach glide path. To compensate, the pilot should try to adjust his
visual glide path to a point beyond the desired touchdown point.
(4) Downsloping terrain: If the terrain surrounding the approach to
a runway is downsloping, the aircraft will appear to be below a normal
approach glide path. If the aircraft flight path is changed because of this
illusion the aircraft will land short of the desired touchdown point.
b. Visibility Restrictions. Atmospheric conditions such as smoke,
dust, glare and darkness may confuse the sense of sight due to the fact that
shadows will be less distinct or even absent. Under any of these conditions
an observer may get the illusion that an object is farther than it really
is. An important consideration for pilots is that these conditions may
create an illusion that the altitude of the aircraft is higher than it
actually is.
c. Runway Lighting. When approaches are made to lighted runways the
intensity of the lights and variances in intensity of the lighting may
create illusions of untrue situations.
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