OPTICAL ILLUSIONS IN AVIATION

Optical Illusions in Aviation

Optical Illusions in Aviation

Illusions in Flight: Problems of Perspective

Most visual illusions that occur in flight happen when few visual cues are available. Perhaps the most common illusion is that of a false horizon, or missing horizon. Breaking out of overcast at night, a pilot might see a road or other grouping of lights that creates the illusion of a horizon. Unless the pilot maintains an instrument scan, he can easily succumb to the natural tendency to align his wings with the illusion (Rossier, 2002).

A similar situation can develop over an area with sparse illumination on a clear, moonless night. In one case, a charter pilot was flying eastbound off the south shore of Long Island on just such a night. Not only were the conditions perfect for flying, but they also happened to be great conditions for cod fishing. The commercial fishing fleet was scattered over the ocean, each boat illuminated by a white light. As the pilot gazed over the scene, the star-studded sky melded into the boat-studded sea, erasing any semblance of a horizon. Scanning the sky for traffic, the pilot unwittingly rolled his aircraft in a 30-degree bank as he attempted to regain the horizon visually. There was a moment of confusion as he glanced at his instruments, realized what had happened, and then rolled wings level (Turner, 1997).

Another form of visual illusion is called auto-kinesis, and this occurs when a pilot fixates on a single light in the sky. If you stare at a bright light cast in a dark background, an illusion occurs wherein the light appears to move. More than one pilot has been fooled by such an illusion when departing into the night sky. Often a bright planet will be mistaken for the landing light of an oncoming aircraft.

The Madness of Motion

The problem of visual illusions can be greater when our inner ear gets involved with the program, as can occur when acceleration and maneuvering create changing g-forces. If we slowly enter a bank, and then suddenly roll out of it, we can suffer from an illusion called “the leans,” in which the motion-sensing mechanisms in our inner ear readily convince us that we have entered a bank in the opposite direction. Likewise, if we recover from a spin that has ceased stimulating our motion-sensing mechanisms, we can perceive a spin in the opposite direction, and re-enter the original spin (McKinney, 2008).

In a similar sense, the “elevator illusion” occurs when turbulence or wind shear creates an abrupt vertical acceleration. The pilot perceives a climb or descent, and applies elevator pressure to correct the misinterpreted signal.

Another such illusion, called the “somatogravic illusion,” can occur during an acceleration or deceleration. In the absence of visual cues, a deceleration can create the sensation of pitching down, and the pilot may pull up to compensate. Such a reaction could cause an inadvertent stall.

Acceleration in the direction of normal flight creates the sensation of pitching ...