Visual illusions are familiar to most of us. As children, we learned that railroad tracks—contrary to what our eyes showed us—don’t come to a point at the horizon.
Aerial Perspective Illusions may make you change (increase or decrease) the slope of your final approach. They are caused by runways with different widths, upsloping ordownsloping runways, and upsloping or downslop ing final approach terrain.
Pilots learn to recognize a normal final approach by developing and recalling a mental image of the expected relationship between the length and the width of an average runway.
A final approach over a flat terrain with an upsloping runway may produce the visual illusion of a high-altitude final approach. If you believe this illusion, you may respond by pitching the aircraft nose down to decrease the altitude, which, if performed too close to the ground, may result in an accident.
A final approach over a flat terrain with a downsloping runway may produce the visual illusion of a low-altitude final approach. If you believe this illusion, you may respond by pitching the aircraft nose up to increase the altitude, which may result in a low-altitude stall or missed approach.
A final approach over an upsloping terrain with a flat runway may produce the visual illusion that the aircraft is higher than it actually is. If you believe this illusion, you may respond by pitching the aircraft nose-down to decrease the altitude, resulting in a lower approach. This may result in landing short or flaring short of the runway and risking a low-altitude stall. Pitching the aircraft nose-down will result in a low, dragged-in approach. If power settings are not adjusted, you may find yourself short of the runway, needing to add power to extend your flare. If you do not compensate with power, you will land short or stall short of the runway.
A final approach over a downsloping terrain with a flat runway may produce the visual illusion that the aircraft is lower than it actually is. If you believe this illusion, you may respond by pitching the aircraft’s nose up to gain altitude. If this happens, you will land further down therunway than you intended.
A final approach to an unusually narrow runway or an unusually long runway may produce the visual illusion of being too high. If you believe this illusion, you may pitch the aircraft’s nose down to lose altitude. If this happens too close to the ground, you may land short of the runway and cause an accident.
A final approach to an unusually wide runway may produce the visual illusion of being lower than you actually are. If you believe this illusion, you may respond by pitching the aircraft’s nose up to gain altitude, which may result in a low-altitude stall or missed approach.
A Black-Hole Approach Illusion can happen during a final approach at night (no stars or moonlight) over water or unlighted terrain to a lighted runway beyond which the horizon is not visible. When peripheral visual cues are not available to help you orient yourself relative to the earth, you may have theillusion of being upright and may perceive the runway to be tilted left and upsloping. However, with the horizon visible you can easily orient yourself correctly using your central vision. A particularly hazardous black-hole illusion involves approaching a runway under conditions with no lights before the runway and with city lights or rising terrain beyond the runway. Those conditions may produce the visual illusion of a high-altitude final approach. If you believe this illusion you may respond by lowering your approach slope.
The Autokinetic Illusion gives you the impression that a stationary object is moving in front of the airplane’s path; it is caused by staring at a fixed single point of light (ground light or a star) in a totally dark and featureless background. This illusion can cause a misperception that such a light is on a collision course with your aircraft .
False Visual Reference Illusions may cause you to orient your aircraft in relation to a false horizon; these illusions are caused by flying over a banked cloud, night flying over featureless terrain with ground lights that are indistinguishable from a dark sky with stars, or night flying over a featureless terrain with a clearly defined pattern of ground lights and a dark, starless sky.