FAA Private Pilot Helicopter (PRH)Human FactorsHard
A helicopter pilot has been in a prolonged, coordinated turn while inside a cloud layer for over a minute. The pilot no longer senses any turning, but the attitude indicator and altimeter show the aircraft is banked and losing altitude rapidly. Believing the helicopter is simply descending wings-level, the pilot pulls back on the cyclic without correcting the bank. What is happening, and what is the danger?
- ACoriolis illusion, causing a sensation of tumbling
- BThe graveyard spiral, causing the bank and descent to steepen
- CSomatogravic illusion, causing a false sense of pitch-up
- DAutokinesis, causing perceived movement of a stationary light
Show answer & explanationAnswer & explanation
Correct answer: B. The graveyard spiral, causing the bank and descent to steepen
After a prolonged constant-rate turn, the inner ear fluid stabilizes and the sensation of turning disappears even though the aircraft remains banked and descending. Pulling back on the cyclic without leveling the wings tightens the turn and increases the descent rate — the classic graveyard spiral.
Why the other options are wrong
- A. Coriolis involves head movement disturbing multiple canals simultaneously, causing tumbling, not this scenario.
- C. Somatogravic illusion relates to acceleration/deceleration cues, not sustained turns.
- D. Autokinesis is a stationary light appearing to move, unrelated to this turn scenario.
Graveyard Spiral
A vestibular illusion where a pilot in a prolonged turn no longer perceives turning, and pulling back on the controls without leveling the wings tightens the spiral and descent.
- Occurs after sustained constant-rate turns in IMC
- Fluid in semicircular canals stabilizes, masking sensation of turn
- Trust instruments, not sensations, to recover
Memory trick: Digging your own grave by pulling back blind in a spiral.