Human Performance and Limitations
What this paper tests
Human performance and limitations asks how the pilot, not the aircraft, fails: hypoxia, hyperventilation, spatial disorientation, sensory illusions, fatigue, stress, decision-making and fitness to fly. Answers usually turn on recognising a symptom early and choosing the correct corrective action.
The main physiological threats
- Hypoxic (altitude), hypemic (carbon monoxide, anaemia), stagnant (G-loading) and histotoxic (alcohol, drugs) hypoxia - only the hypoxic type is corrected by oxygen alone.
- Slow onset above 10 000 ft in unpressurised aircraft: euphoria, poor judgement and cyanosis appear before the pilot notices. Time of useful consciousness falls sharply with altitude. Widely applied rules require oxygen for more than 30 minutes above 12 500 ft and continuously above 14 000 ft.
- Hyperventilation gives dizziness, tingling and cramps; if in doubt treat it as hypoxia - slow the breathing rate, talk aloud and use 100% oxygen if available.
- Carbon monoxide is odourless; suspect it from exhaust smells, heater use and a deteriorating pilot. Cherry-red skin is a late sign.
- Decompression sickness and trapped gas pain follow rapid altitude change; do not fly with a heavy cold.
Disorientation and illusions
- Somatogravic illusion: acceleration on take-off feels like a nose-up attitude, so the pilot pushes forward - trust the attitude indicator.
- The leans and somatogyral illusions follow prolonged turns; recovery is by reference to instruments, not by feel.
- Visual illusions: a black-hole approach makes you fly low (fly a higher, steeper path), a wide runway makes you flare high, a narrow runway makes you flare late; sloping terrain and false horizons mislead the night VFR pilot.
Worked example
On a dark night after take-off you sense the aircraft pitching up and instinctively push the yoke forward, but the attitude indicator shows level flight. This is the somatogravic illusion caused by linear acceleration. The correct action is to cross-check the instruments, hold the attitude and altimeter steady, and ignore the sensation until it fades.
Traps that cost marks
- Treating hyperventilation as the only explanation and delaying oxygen.
- Confusing IMSAFE (pilot fitness) with PAVE (pilot, aircraft, environment, external pressures).
- Believing night vision is best at the centre of the eye - it is best 5–10° off-centre, and dark adaptation takes about 30 minutes.
- Forgetting that dehydration, smoking and fatigue lower the altitude at which hypoxia appears.