FAA Private Pilot Helicopter (PRH)Human FactorsHard
A pilot has been in a shallow, gradual left turn for several minutes without visual reference to the horizon. Upon abruptly leveling the wings, the pilot experiences a strong sensation that the aircraft is now banking to the right, even though the attitude indicator shows level flight. Which illusion is this?
- ASomatogravic illusion
- BCoriolis illusion
- CThe leans
- DGraveyard spiral
Show answer & explanationAnswer & explanation
Correct answer: C. The leans
The leans occur when a gradual banking motion goes undetected by the vestibular system, and an abrupt return to level flight causes the pilot to sense a bank in the opposite direction. The pilot must trust the instruments and resist the urge to re-bank the aircraft.
Why the other options are wrong
- A. Somatogravic illusion relates to linear acceleration being felt as pitch change, not banking sensation.
- B. Coriolis illusion is caused by moving the head during a sustained turn, producing a tumbling sensation, not simply misjudging bank angle after leveling.
- D. Graveyard spiral involves a prolonged turn feeling like level flight, often leading to a diving spiral, not this sudden opposite-bank sensation.
The Leans
A spatial disorientation illusion in which an abrupt return to level flight after a prolonged, gradual, undetected turn causes a false sensation of banking in the opposite direction.
- Most common vestibular illusion experienced by pilots
- Caused by the inner ear's inability to detect very slow angular accelerations
- Correct response is to trust flight instruments over bodily sensations
Memory trick: 'Lean on the level' — trust the gauges when your body says lean.