Human Performance and Limitations
Human Performance and Limitations tests the pilot as a system component: hypoxia, hyperventilation, spatial disorientation, fatigue, stress, vision, hearing, information processing, and crew decision-making. Questions are applied scenarios - what you would feel, why your judgement degrades, and what to do about it.
Hypoxia
Hypoxic hypoxia from altitude is the key case. Time of useful consciousness is about 3–5 minutes at 25,000 ft, 1–2 minutes at 30,000 ft and 15–20 seconds at 40,000 ft. Early signs such as euphoria, tingling and poor judgement are easily missed, so treat any suspicion as real and descend.
Hyperventilation
Rapid breathing blows off carbon dioxide, causing dizziness, tingling and cramps that mimic hypoxia. Slow the breathing rate; if symptoms persist, assume hypoxia and use oxygen.
Spatial disorientation
The somatogravic illusion produces a false sensation of climbing during acceleration; the leans follow a slow roll. In IMC, trust the instruments; at night in VMC, use them too.
Vision and fatigue
Rods handle night vision and work best with off-centre viewing, so do not stare directly at a dim target. Fatigue degrades reaction time and vigilance long before you feel sleepy; controlled rest and a sterile cockpit help.
Worked example
A pilot at 25,000 ft loses pressurisation. Time of useful consciousness is roughly 3–5 minutes, but judgement falls earlier. The correct action is oxygen first, then immediate descent with ATC notified - not troubleshooting.
Traps
Confusing hypoxia with hyperventilation; believing bright light improves night vision; and assuming coffee or willpower reverses fatigue.