Hypoxia and Fatigue on a Night Sector
A CPL holder has been on duty 10 h 20 min and is on the fourth sector of the day, a 1 h 50 min night VFR flight in an unpressurized aircraft. The pilot woke at 05:00 after 5 h sleep and has had one meal and little water. Cruising altitude is 11,500 ft for 45 min. About 20 min into cruise, the pilot notices tingling in the fingers, mild headache, light-headedness and a sense of euphoria. The pulse oximeter reads 88% and falling. The destination is 40 min away with VFR weather; a suitable airport is 15 min away. There is no supplemental oxygen on board. The pilot must decide what is happening and what to do.
1. Identify the likely physiological factors and explain why the altitude is significant.
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The symptoms and SpO2 of 88% suggest hypoxia, made worse by fatigue, dehydration and night operation. At 11,500 ft in an unpressurized aircraft, alveolar oxygen partial pressure is well below sea level, and even a healthy pilot can show impaired judgement and coordination. The euphoria is particularly dangerous because it reduces the pilot's ability to recognize the deterioration. Fatigue from 10 h 20 min duty, only 5 h sleep, one meal and little water lowers tolerance further. The falling saturation confirms that this is not just a feeling of tiredness. The pilot should treat the situation as hypoxia until proven otherwise, not press on because the destination is only 40 min away.
2. State the immediate actions and the order in which you would take them.
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First, descend immediately toward 10,000 ft or lower; do not wait to see whether symptoms improve. If oxygen were available, use it, but here there is none. Advise ATC of the problem and request a descent and diversion to the nearer airport, 15 min away. Use the autopilot if available to reduce workload, but monitor it. Avoid rapid or abrupt manoeuvres, and do not continue to the original destination. Land as soon as practicable and do not fly another sector until recovered. The key reasoning is that judgement is already impaired, so the decision to descend must be made before the pilot feels worse.
3. What prevention and regulatory considerations apply to this kind of flight?
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The flight should have been planned with supplemental oxygen for prolonged cruise at high altitude, or the cruise altitude should have been kept lower. Duty and rest planning should account for early starts, night flying and multiple sectors; 5 h sleep before a 10 h duty day is not adequate. Hydration and food also matter. The pilot should recognize that oxygen requirements are not just a legal threshold; they are a performance issue. After landing, the pilot should not self-certify for further flight while symptomatic, and should seek medical advice if symptoms persist. The operator should review the sector planning and oxygen policy.