Human Performance and Limitations
Human Performance and Limitations
This domain tests physiology and psychology in the instrument environment: hypoxia, hyperventilation, disorientation, fatigue and automation behaviour. Examiners favour scenario questions where a pilot's sensation conflicts with the instruments.
Physiology
- Hypoxia types: hypoxic (altitude), hypemic (CO, anaemia), stagnant (G, cold), histotoxic (alcohol, drugs). Time of useful consciousness at FL 350 is roughly 30–60 seconds; at FL 400, 15–20 seconds. Mask on first, then descend.
- Hyperventilation mimics hypoxia (dizziness, tingling, visual disturbance). Distinguish by breathing rate and by response to slowing the rate; if in doubt, treat as hypoxia and use oxygen.
- Decompression: don oxygen, don mask, initiate emergency descent to 10,000 ft or MSA, avoid reverse block in ears and sinuses.
Illusions and disorientation
- Somatogravic: linear acceleration is felt as pitch-up, so on a night go-around the pilot pushes forward and flies into terrain.
- Somatogyral (the leans): recovery from a prolonged turn creates a false turn sensation - trust the attitude indicator.
- Black-hole approach: no ground references make the aircraft fly a lower approach than normal.
- Empty-field myopia and autokinesis in dark, featureless night skies.
Worked example
Night departure, overcast, no horizon. On go-around with TOGA thrust the pilot feels a strong nose-up sensation and pushes forward. Instruments show a 10° nose-down attitude and decreasing altitude. The correct response is to hold the flight director pitch attitude, level the wings and ignore the sensation - the otoliths are responding to linear acceleration, not to pitch.
Traps
- Treating hyperventilation as harmless while true hypoxia develops.
- Believing a sensation over a serviceable attitude indicator.
- Ignoring fatigue and circadian low points (early morning) when assessing crew decisions.