Human Performance and Limitations: physiology, illusion, CRM
Oxygen and altitude
Above about 10 000 ft without supplementary oxygen, hypoxia develops. Time of useful consciousness is 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; rapid decompression shortens these figures. Recognise hypoxia in yourself: euphoria, tingling, cyanosis, poor judgement - the last faculty to fail is often the one needed to notice.
Other physiology
Hyperventilation mimics hypoxia; in doubt, give 100% oxygen and descend. Spatial disorientation comes from vestibular illusions (somatogravic, somatogyral, coriolis) and visual illusions (black-hole approach, runway slope, false horizon). Trust the instruments. Also know night vision and rod/fovea distribution, dark adaptation, carbon monoxide, decompression sickness, barotrauma, noise and vibration, and +Gz effects (grey-out, blackout) versus −Gz (red-out).
Psychology and CRM
Fatigue is cumulative and circadian; the window of circadian low is roughly 02:00–06:00. Know stress, workload and situational awareness; error models (SHELL, Reason's Swiss cheese); the difference between a slip and a mistake; assertion, briefing, cross-check and the sterile flight deck rule.
Worked example
A crew at FL350 loses pressurisation. Time of useful consciousness is about 30–60 seconds, so masks go on first and discussion follows. Emergency descent to 10 000 ft (or MSA) at Vmo/MMO with spoilers gives roughly 5 000–6 000 ft/min; FL370 to 10 000 ft takes about 5 minutes.
Traps
Confusing hypoxia with hyperventilation; assuming a slow leak is less dangerous than an explosive one; forgetting that alcohol and some medicines increase susceptibility.