Human Performance and Limitations
Human Performance and Limitations tests the pilot as a system: physiology, perception, decision-making and crew resource management.
Physiology
Hypoxia reduces oxygen to the brain; early signs include euphoria, poor judgement, headache and cyanosis. Time of useful consciousness falls with altitude. Hyperventilation produces dizziness and tingling; it is treated by slowing the breathing rate, not by more oxygen alone. Carbon monoxide from a heater is odourless and causes headache and confusion. Fatigue, dehydration and alcohol degrade performance before subjective awareness.
Perception and disorientation
The vestibular system cannot distinguish acceleration from tilt. Somatogravic illusion occurs on rapid acceleration, when the pilot feels nose-high and may push forward; on a dark go-around this can be fatal. The leans and somatogyral illusions follow prolonged turns. Visual illusions include black-hole approach, runway slope and width. Trust the instruments and cross-check.
Decision-making
Use PAVE (Pilot, Aircraft, enVironment, External pressures) and IMSAFE for fitness. CRM includes briefings, callouts, task sharing and assertiveness. Scuba diving requires a no-fly interval; medication and self-medication are disqualifying until cleared.
Worked example
At night after a rapid acceleration on a go-around, you feel the aircraft pitching up. The correct response is to cross-check the attitude indicator and airspeed, establish the required pitch and climb attitude, and ignore the false sensation. Do not push forward to 'correct' a nose-high illusion; that can produce a dive into terrain.
Traps
Waiting for obvious hypoxia symptoms; treating hyperventilation with oxygen only; assuming 'see and avoid' works in IMC; and ignoring fatigue because you feel motivated.