As the name suggests, it involves an approach to landing during the night where there is nothing to see between the aircraft and the intended runway, there is just a visual, “black–hole”.
The black hole illusion, sometimes called the featureless terrain illusion, fools pilots into thinking they are higher than they actually are, causing them to fly dangerously low approaches.A visual illusion known as “black hole effect” is another inherent risk of night visual approaches. The ‘black-hole’ approach illusion can also create great difficulty for the pilot.
A ‘black-hole’ approach is made at night, in the absence of a discernible horizon, over unlit terrain onto a lit runway. Without peripheral visual cues such as ground lights or horizon the pilot tends to feel that his aircraft is stable and correctly positioned and that the runway moves or is poorly positioned . This illusion makes the ‘black-hole’ approach dangerous and difficult, and can result in a landing far short of the runway.
Of the senses, vision is the most important for safe flight. However, various terrain features and atmospheric conditions can create optical illusions. These illusions are primarily associated with landing.Take a look at the major illusions leading to landing errors with an excerpt from the Pilot’s Handbook of Aeronautical Knowledge.
Runway Width Illusion
A narrower-than-usual runway can create an illusion that the aircraft is at a higher altitude than it actually is, especially when runway length-to-width relationships are comparable. The pilot who does not recognize this illusion will fly a lower approach, with the risk of striking objects along the approach path or landing short. A wider-thanusual runway can have the opposite effect with the risk of the pilot leveling out the aircraft high and landing hard or overshooting the runway.
Runway and Terrain Slopes Illusion
An upsloping runway, upsloping terrain, or both can create an illusion that the aircraft is at a higher altitude than it actually is. The pilot who does not recognize this illusion will fly a lower approach. Downsloping runways and downsloping approach terrain can have the opposite effect.
Featureless Terrain Illusion
An absence of surrounding ground features, as in an overwater approach over darkened areas or terrain made featureless by snow, can create an illusion that the aircraft is at a higher altitude than it actually is. This illusion, sometimes referred to as the “black hole approach,” causes pilots to fly a lower approach than is desired.
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.
Atmospheric haze can create an illusion of being at a greater distance and height from the runway. As a result, the pilot has a tendency to be low on the approach. Conversely, extremely clear air (clear bright conditions of a high altitude airport) can give the pilot the illusion of being closer than he or she actually is, resulting in a high approach that may result in an overshoot or go around. The diffusion of light due to water particles on the windshield can adversely affect depth perception. The lights and terrain features normally used to gauge height during landing become less effective for the pilot.
Flying into fog can create an illusion of pitching up. Pilots who do not recognize this illusion often steepen the approach abruptly.
Ground Lighting Illusions
Lights along a straight path, such as a road or lights on moving trains, can be mistaken for runway and approach lights. Bright runway and approach lighting systems, especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway. The pilot who does not recognize this illusion will often fly a higher approach.
Almost every pilot will have experienced some of these illusions at sometime or other during their flying career. Those that make the effort to learn about these illusions will be better prepared for their next flight. Those who are better prepared and have a better understanding of their sensory limitations are less likely to become victims of illusions during the approach and landing phases of flight.