Human Performance and Limitations
Human Performance and Limitations tests the pilot as a system: hypoxia, disorientation, fatigue, decision-making and fitness. The exam rewards recognising a degraded state early, not reciting physiology.
Oxygen and altitude
Above about 10,000 ft, supplemental oxygen is needed for prolonged flight; night vision degrades from about 5,000 ft. Time of useful consciousness falls rapidly with altitude: roughly 3–5 min at 25,000 ft, 1–2 min at 30,000 ft, and 30–60 s at 35,000 ft. Hypoxia impairs judgement before the pilot notices.
Disorientation and illusions
The somatogravic illusion makes acceleration feel like a climb; the leans follow a slow roll; a black-hole approach makes a high glide path look normal. Trust the instruments in IMC and at night.
Fitness and decisions
Use IMSAFE. Alcohol, fatigue, medication and CO poisoning all degrade performance. Scuba diving requires a conservative no-fly interval. Hyperventilation causes tingling and dizziness; hypoxia causes similar symptoms, so slow the breathing and descend/check oxygen.
Worked example
A rapid depressurisation at FL350 gives a TUC of about 30–60 s. The first action is mask on and establish oxygen; then communicate and descend. Reaching for a checklist first consumes the most valuable seconds.
Traps
Assuming 'I feel fine' rules out hypoxia; treating hyperventilation as proof of no hypoxia; flying with a hangover; ignoring CO from cabin heat; continuing after a diving exposure.