Definition
A form of spatial disorientation in which the pilot has the false sensation that the aircraft is banked when it is actually flying wings-level, caused by the inner ear failing to detect a slow roll and then registering the correction back to level as a roll in the opposite direction. The pilot tends to lean their body in the direction of the perceived bank to feel upright.
Plain English
A false feeling that you are tilted to one side when the aircraft is actually flying straight and level. Your inner ear missed a slow turn, so when you correct back to level, it feels like you have rolled the wrong way — and you instinctively lean to compensate.
Context Anchor
Encountered in instrument flying, especially in clouds, haze, or darkness when the pilot cannot use the outside horizon to judge whether the airplane is level.
Derivation
Named for the most visible symptom: pilots experiencing it physically lean their bodies in the direction of the imagined bank, trying to sit 'upright' relative to a tilt that isn't there.
Why Pilots Care
A pilot may apply incorrect control inputs to correct the false sensation, risking loss of control in instrument conditions.
Analogy
Like the tilting feeling that lingers for a moment after you stop turning in an office chair.
Grounding Statement
In instrument conditions, your inner ear can feel motion that the airplane is not actually making, so the instruments must be trusted over the feeling.
Intuition Check
The leans does not mean ordinary poor posture or simply leaning in the seat. In instrument flying, it means a specific false body sensation that can make level flight feel tilted.
Example Sentence 1
After rolling out of a long, gradual turn in the clouds, the pilot got the leans and had to consciously trust the attitude indicator to keep the wings level.
Example Sentence 2
Recognizing the leans early allowed the pilot to ignore the body sensation and rely strictly on the instruments.