FAA Private Pilot Helicopter (PRH)Human FactorsMedium
On a moonless night, a helicopter pilot is flying toward a sloping layer of city lights on a hillside that resembles a level horizon. Without realizing it, the pilot banks the helicopter to align with the sloping lights, resulting in an actual left bank while feeling wings-level. Which illusion caused this situation?
- AFalse horizon
- BSomatogravic illusion
- CGraveyard spiral
- DAutokinesis
Show answer & explanationAnswer & explanation
Correct answer: A. False horizon
A false horizon illusion occurs when a pilot mistakes a sloping line of ground lights, a cloud bank, or a starlit horizon for the actual horizon, causing the aircraft to be banked or pitched incorrectly while the pilot believes the attitude is normal.
Why the other options are wrong
- B. Somatogravic illusion is caused by acceleration, not by visual misalignment with lights.
- C. Graveyard spiral results from a prolonged turn's fading sensation, not misjudging ground lights.
- D. Autokinesis is a stationary light appearing to move, not a sloped alignment error.
False Horizon Illusion
A visual illusion in which a pilot mistakes a sloping cloud formation, ground light pattern, or the milky way for the actual horizon, leading to an incorrect aircraft attitude.
- Common at night or in reduced visibility
- Pilot subconsciously aligns aircraft with the false reference
- Cross-checking flight instruments prevents this illusion
Memory trick: City lights on a hillside can fake a tilted horizon.