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Visual Illusions

False Horizon​

Several phenomena can create a visual line that a pilot might mistake for a horizon.

  • These can include:
    • A sloping cloud formation
    • An obscured horizon
    • An aurora borealis
    • A dark scene spread with ground lights and stars
    • Certain geometric patterns of ground lights

Runway Width Illusion​

  • A narrower-than-usual runway can create an illusion that the aircraft is at a higher altitude than it actually is
  • Likewise, a wider-than-usual runway can create an illusion that the aircraft is at a lower altitude than it actually is

Sloping Terrain​

  • An upsloping runway or upsloping terrain can create an illusion that the aircraft is at a higher altitude than it actually is
  • A downsloping runway or downsloping terrain can create an illusion that the aircraft is at a lower altitude than it actually is

Featureless Terrain​

An absence of surrounding ground features, for instance a dark overwater approach, or featureless terrain from snow, can create an illusion that the aircraft is at a higher altitude than it actually is.

This is sometimes called a "black hole approach," and causes pilots to fly a lower approach than is desired.

Water Refraction​

Rain on the windscreen can create an illusion of being at a higher altitude due to the horizon appearing lower than it is. This can result in the pilot flying a lower approach.

Haze​

Atmospheric haze can create an illusion of being at a greater distance and height from the runway.

Fog​

Flying into fog can create an illusion of pitching up. Pilots who do not recognize this illusion often steepen the approach abruptly.

References​

AIM 8-1-2 Pilot's Handbook of Aeronautical Knowledge pg. 17-6