Human Performance and Limitations
Human Performance and Limitations treats the pilot as a system component: hypoxia, decompression, hyperventilation, spatial disorientation, sensory illusion, vision and hearing, fatigue, stress, alcohol and drugs, and crew resource management. Questions ask for recognition, first response and the physiological reason behind it.
Oxygen and decompression
- Time of useful consciousness: roughly 20–30 minutes at FL180, 3–5 minutes at FL250, 1–2 minutes at FL300, 30–60 seconds at FL350 and 15–20 seconds at FL400.
- Slow, rapid and explosive decompression differ mainly in the speed of onset; signs include ear and gut pain, fizzing of body fluids and mist in the cabin.
- First actions: oxygen mask on, establish crew communications, then emergency descent to FL100 or the minimum safe altitude.
Hypoxia and hyperventilation
- Hypoxic hypoxia produces euphoria, poor judgement and cyanosis; treat with 100% oxygen and descent.
- Hyperventilation lowers carbon dioxide, causing dizziness, tingling and tetany; correct with controlled breathing, but treat as hypoxia until proven otherwise.
Disorientation and illusion
- Somatogravic illusion (acceleration feels like a climb), somatogyral illusion after sustained rotation, the leans, black-hole approach, runway width illusion and autokinesis.
- The answer is always to trust the instruments and use a disciplined scan.
Human factors
- Fatigue, sleep debt and circadian low points degrade judgement before the pilot notices.
- Alcohol: an 8-hour bottle-to-throttle interval plus the blood-alcohol limit set in CAR-MED; smoking and carbon monoxide reduce oxygen-carrying capacity.
- CRM: briefing, assertiveness, cross-check and a sterile flight deck during critical phases.
Worked example
Rapid decompression at FL350. Time of useful consciousness is only 30–60 seconds, so the mask goes on first, then crew communications and 100% oxygen. Descending at 6,000 ft/min from FL350 to FL100 covers 25,000 ft in about four minutes - far longer than the time available, which is why oxygen precedes descent.
Traps
- Starting the descent before putting the mask on.
- Assuming absence of symptoms means adequate oxygenation.
- Confusing hyperventilation with hypoxia and treating the wrong one.