The Leans

The leans is the most common type of spatial disorientation experienced by aviators. Through stabilization of the fluid in the inner ear's semicircular canals, a pilot may perceive straight and level flight while actually flying in a banked turn, a false perception typically caused by a quick return to level flight after a gradual, prolonged turn the pilot failed to notice. The illusion consists of a false perception of angular displacement about the roll axis, so it becomes an illusion of bank, and it is often associated with a vestibulospinal reflex that causes the pilot to physically lean in the direction of the falsely perceived vertical. Other explanations offered for the leans point to deficiencies in both the otolith organs and the semicircular ducts, the inner ear's own sensory mechanisms for detecting motion and orientation.