Human Performance and Limitations
Oxygen and altitude
Hypoxia produces euphoria, tingling, cyanosis and impaired judgement. Time of useful consciousness at FL350 is roughly 30–60 seconds; at FL400 about 15–20 seconds. Hyperventilation gives similar dizziness but is relieved by controlled breathing; hypoxia is not.
Disorientation
Somatogravic illusion (acceleration feels like a climb), the leans, and black-hole approaches at night all feed misleading inputs. Trust the instruments and cross-check.
Fatigue and fitness
Circadian low points fall around 03:00–05:00 and 15:00–17:00. Sleep debt, alcohol, some medications and smoking degrade performance. Many states apply an eight-hour bottle-to-throttle rule and a 0.02% blood alcohol limit.
Vision and hearing
Rods serve night peripheral vision; look slightly to one side of a dim object at night. Noise-induced hearing loss is cumulative and permanent.
Worked example
A pilot at FL350 suffers a slow decompression, becomes confused and stops using oxygen. The useful consciousness window there is 30–60 seconds, so the correct immediate action is to don the mask first and then start the emergency descent. Trying to diagnose the problem before donning oxygen consumes the time available.
Traps
Confusing hyperventilation with hypoxia; assuming sunglasses improve night vision (they reduce it); believing caffeine cures fatigue; relying on subjective feelings rather than the oxygen mask and checklist.