Sensory illusions in aviation
Pilots may experience disorientation and loss of perspective, creating illusions that range from false horizons to sensory conflict with instrument readings or the misjudging of altitude over water.
[2] Illusions involving the semicircular and somatogyral canals of the vestibular system of the ear occur primarily under conditions of unreliable or unavailable external visual references and result in false sensations of rotation.
[3][4]: 4 The reason a pilot can be unaware of such an attitude change in the first place is that human exposure to a rotational acceleration of ~1 degrees per second²[5] or less is below the detection threshold of the semicircular canals.
In response to such an illusion, a pilot will tend to roll back in the direction of the original bank in a corrective attempt to regain the perception of a level attitude.
[4]: 5 Attempting to adjust the controls in this way will have the effect of tightening the radius of the turn and eventually quickening the rate of descent until the pilot is visually cued to the nature of the error or contact with the terrain occurs.
[9] This involves the simultaneous stimulation of two semicircular canals and is associated with a sudden tilting (forward or backwards) of the pilot's head while the aircraft is turning.
[10] This can occur when tilting the head down (to look at an approach chart or to write on the knee pad), up (to look at an overhead instrument or switch), or sideways.
These illusions involving the utricle and the saccule of the vestibular system are most likely to occur under conditions with unreliable or unavailable external visual references.
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 pilot flying an aircraft where the cockpit height relative to the ground is vastly higher or lower than they are used to can cause a similar illusion in the last part of the approach.
As a result, this can lead to the pilot experiencing glide path overestimation (GPO) because of the lack of peripheral visual cues, especially, below the aircraft.
[15] In addition, with no peripheral visual cues allowing for an orientation relative to the earth there can be an illusion of the pilot being upright and the runway being tilted and sloping.
[13]: 3 The autokinetic illusion occurs at night or in conditions with poor visual cues and gives the pilot the impression that a stationary light source is on a collision course with the aircraft.
[4][13]: 4 Planets or stars in the night sky often cause the illusion, having been mistaken for landing lights of oncoming aircraft, satellites, or even UFOs.
Glassy water may also result in an unusually clear view of the lake or sea floor and abnormally brilliant reflections of clouds or shore features; these extraneous visual cues may further disorient the pilot.
