FAA Private Pilot Helicopter (PRH)Human FactorsMedium
A helicopter pilot regularly flies early morning cargo runs, departing at 0330 after only four hours of sleep the previous night due to a late arrival the day before. He reports feeling unusually slow to react and has trouble concentrating during the flight, even though he does not feel overtly sleepy. This performance decline is best explained by which factor?
- AHyperventilation
- BHypoxic hypoxia
- CCircadian rhythm disruption
- DSomatogravic illusion
Show answer & explanationAnswer & explanation
Correct answer: C. Circadian rhythm disruption
Human performance and alertness follow an internal circadian rhythm, with a natural low point typically between 0300 and 0500. Flying during this window, especially with reduced sleep, degrades reaction time and cognitive performance even without overt sleepiness.
Why the other options are wrong
- A. Hyperventilation is a breathing response to stress or anxiety, unrelated to time of day.
- B. Hypoxic hypoxia is caused by insufficient oxygen at altitude, not time-of-day effects.
- D. Somatogravic illusion is a vestibular misperception from acceleration, not a fatigue/circadian effect.
Circadian Rhythm Disruption
Degraded alertness and performance caused by flying during the body's natural low point in its 24-hour internal clock, typically between 0300 and 0500.
- Circadian low point is roughly 0300-0500 for most people
- Reduced sleep amplifies circadian-related performance decline
- Irregular schedules and time zone changes worsen the effect
Memory trick: The body's clock hits its low point in the dead of night.