Heater Leak at 9,500 Feet
Pilot flying a PA-28 at 9,500 ft MSL for 2 hours 20 minutes on a night VFR flight from Sendai to Akita. Outside temperature is -5°C. Cabin heat has been full on for 90 minutes. The pilot develops a dull headache, nausea, and slight confusion, thinks it is fatigue, and turns the heat up. The passenger is asleep. The pilot notices a faint exhaust smell but dismisses it. The aircraft has no CO detector and no supplemental oxygen. The pilot had 3 hours of sleep the previous night and drank coffee. The engine runs smoothly, fuel flow and EGT are normal. Only 25 minutes remain to destination. The aircraft's heater uses a muff around the exhaust.
1. What is the most likely cause of the symptoms, and why is hypoxia less likely at 9,500 ft?
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The most likely cause is carbon monoxide (CO) poisoning from a leaking exhaust heater muff. CO binds haemoglobin with roughly 200-250 times the affinity of oxygen, reducing oxygen delivery and causing headache, nausea, confusion, and eventually unconsciousness. The faint exhaust smell and the timing with full cabin heat are strong clues. At 9,500 ft, mild hypoxia is possible, but a healthy pilot would not normally develop confusion after 2 hours at that altitude without a pressurization or oxygen failure; the heater exposure is the more specific cause. Treat it as CO until proven otherwise and do not rely on the absence of cyanosis.
2. What immediate actions should the pilot take?
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Turn off the cabin heat, open fresh-air vents or a window, descend, and land at the nearest suitable airport. Use 100% oxygen if carried. Declare an emergency if there is confusion or the passenger is affected. Do not continue the remaining 25 minutes to destination; CO can impair judgement and worsen rapidly. After landing, seek medical evaluation for both occupants and do not fly until cleared. The pilot's own confusion makes checklist use and ATC assistance important.
3. What preflight and in-flight practices reduce this risk?
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Preflight inspection should include the exhaust system, heater muff and shroud, and a CO detector; the heater should be tested on the ground and used intermittently, not full-on for 90 minutes. In flight, any headache, nausea, or confusion with heat on should prompt immediate heat off, vents open, and descent. Brief passengers on symptoms. Managing fatigue also matters, but it does not explain the exhaust smell and the heat association.