What is recognized as the most common vestibular illusion?

The Leans is recognized as the most common vestibular illusion experienced by pilots. This illusion occurs when a pilot experiences an unanticipated bank angle, leading to a false sensation of orientation. It typically happens during flight when inner ear signals suggesting vertical or horizontal alignment conflict with visual cues from the cockpit or the external environment. Pilots may mistakenly perceive that the aircraft is level when it is actually banked, which can lead to inappropriate control inputs. Understanding the Leans is crucial for pilots, as it highlights the importance of relying on instruments rather than solely on sensory perceptions, particularly in conditions with limited horizon references.

In contrast to this, the other options refer to other types of vestibular illusions. The Graveyard Spin occurs when a pilot becomes disoriented during a prolonged turn and may misinterpret the aircraft's vertical position. The G-Excess Effect relates to physiological responses under high G-forces and can lead to loss of consciousness or spatial disorientation. The Oculogyral Illusion is experienced when a pilot continues to feel a rotational motion after the aircraft has stopped turning. Each of these illusions can impact pilot performance but the Leans stands out as the most frequently encountered in routine flight operations.