Human Performance and Limitations
This domain tests the pilot as a system component: how the body behaves at altitude, how the senses mislead, how fatigue and stress degrade judgement, and how crew resource management prevents small errors becoming accidents.
The atmosphere and the body
Hypoxia is the key exam topic. Time of useful consciousness falls sharply with altitude: roughly 20–30 minutes at FL180, 3–5 minutes at FL250, 30–60 seconds at FL350 and 15–20 seconds at FL400. Hypoxic hypoxia is low oxygen in the air breathed; hypemic is the blood's inability to carry it (carbon monoxide, anaemia); stagnant is poor circulation; histotoxic is cell poisoning. Hyperventilation produces dizziness, tingling and cramp and can mimic hypoxia - if in doubt in flight, give 100% oxygen and control the breathing rate. Rapid decompression requires oxygen first, then an emergency descent. Barotrauma hits the ears and sinuses, worst on descent; do not fly with a heavy cold.
The senses
Dark adaptation takes about 30 minutes; use off-centre viewing at night because the fovea is rod-poor. Vestibular illusions include the leans, somatogravic illusion (acceleration feels like a climb), vection and autokinesis; visual illusions include the black hole approach and a false horizon. Spatial disorientation is beaten by reference to instruments, not by feel.
Fatigue, stress and error
Fatigue is cumulative, interacts with circadian low points (roughly 02:00–06:00 and mid-afternoon), and produces fixation and slowed reaction. Stress can be useful up to a point and then becomes disabling. Error models include SHELL (software, hardware, environment, liveware) and Reason's Swiss cheese. CRM covers communication, leadership, workload sharing and structured decision making; the aim is to trap errors before they propagate.
Worked example
A pilot finishes drinking at 23:00 with an estimated blood alcohol of 0.06%. The flight is at 07:30. Elimination runs at about 0.015% per hour, so 8.5 hours removes roughly 0.13% - the alcohol may be gone, but the bottle-to-throttle interval, the local rule against flying with any alcohol, and the lost sleep remain disqualifying.
Traps that cost marks
Treating hyperventilation and hypoxia as opposites and withholding oxygen; confusing greyout with blackout; and assuming fatigue can be overcome by willpower.