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SOMATOGYRAL ILLUSION

Somatogyral illusion or the 'leans' is a perceptual distortion experienced by pilots during prolonged turns or rotation, where the inner ear’s sensitivity to angular motion and inertia can lead to a false sense of the aircraft’s orientation after returning to straight flight. This can cause the pilot to incorrectly perceive the aircraft’s bank angle or attitude.

The 'leans' can occur under two common circumstances in flight:

1. Wings level after a gentle slow turn: If a pilot begins a very gentle and slow turn where the movement of the inner ear's liquid is too slight to activate the hair cells. Consequently, although the aircraft is turning, the balance mechanism senses no change. When the pilot returns to straight and level flight afterward, the inner ear perceives this as a turn from straight and level flight. The pilot may feel as if the aircraft is still turning, even though it is actually straight and level.

2. Wings level after a prolonged turn: During a prolonged turn where the aircraft remains in a banked position long enough for the hair cells in the inner ear canals to fully erect. Upon rolling out of the turn, the movement of the hair cells gives a false sensation of turning in the opposite direction, despite the aircraft being level in reality.

In both scenarios described above, the pilot experiences conflicting signals: visually, they perceive the aircraft as level, while their vestibular system indicates a turning sensation. This discrepancy between what is seen and what is felt can lead to spatial disorientation and challenges in accurately perceiving the aircraft's actual orientation in flight.