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.