Sensory illusions in aviation

Because human senses are adapted for use on the ground, navigating by sensory input alone during flight can be dangerous: sensory input does not always accurately reflect the movement of the aircraft, causing sensory illusions. These illusions can be extremely dangerous for pilots.

The vestibular system consists of the otolith organs and the semicircular canals. Illusions in aviation are caused when the brain cannot reconcile the vestibular and visual inputs. The semicircular canals, of which there are three recognizing accelerations in pitch, yaw, and roll, are stimulated by angular accelerations; the otolith organs, the saccule and utricle, are stimulated by linear accelerations. Stimulation of the semicircular canals occurs when movement of the endolymph inside the canals causes movement of the crista ampullaris and the hair cells within them. Stimulation of the otolith organs occurs when gravitational forces or linear accelerations cause movement of the otolith membrane, the otoliths, and the hair cells of the macula.

Somatogyral illusions occur as a result of angular accelerations stimulating the semicircular canals. Somatogravic illusions, on the other hand, occur as a result of linear accelerations stimulating the otolith organs.

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. These include the leans, the graveyard spin and spiral, and the Coriolis illusion.

This is the most common illusion during flight, and can be caused by a sudden return to wings-level flight following a gradual application of bank that had gone unnoticed by the pilot. 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 degree per second squared or lower is below the detection threshold of the semicircular canals. Rolling wings-level from such an attitude may cause an illusion that the aircraft is banking in the opposite direction. 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.

...
Wikipedia