FAA Private Pilot Helicopter (PRH)Human FactorsHard
A pilot is experiencing a strong illusion of pitching up during a helicopter approach over sloping terrain at night. The pilot responds by pushing the cyclic forward, which decreases the collective and power, resulting in a dangerously low and fast approach. This scenario is characteristic of which visual illusion?
- ASomatogravic illusion
- BAutokinesis
- CUpsloping terrain illusion
- DFalse horizon
Show answer & explanationAnswer & explanation
Correct answer: C. Upsloping terrain illusion
The upsloping terrain illusion, also known as 'black hole approach' or 'runway gradient illusion,' causes a pilot to perceive that they are too high when approaching an upslope, leading to a natural tendency to fly a lower approach. Conversely, a downsloping terrain can make a pilot feel too low, leading to a higher approach. At night, with limited visual cues, this illusion is particularly dangerous.
Why the other options are wrong
- A. Somatogravic illusion is caused by rapid acceleration/deceleration, making a pilot feel like they are pitching up/down, which is not the primary cause here.
- B. Autokinesis is the illusion of a stationary light moving when stared at in a dark environment, not related to terrain slope.
- D. False horizon occurs when confusing sloped cloud formations or ground lights for the horizon, not specifically tied to terrain slope affecting pitch perception.
Upsloping Terrain Illusion
A visual illusion where an approach over upsloping terrain (especially at night) makes a pilot perceive they are too high, leading to a dangerously low and fast approach. The opposite occurs with downsloping terrain.
- Occurs over sloping terrain (upslope or downslope).
- At night, with limited visual cues, it is exacerbated.
- Upslope: Pilot feels too high, flies lower approach.
- Downslope: Pilot feels too low, flies higher approach.
Memory trick: Slope tricks your eyes, making the sky a lie.