Cabin Heater Symptoms at Night
You are a CPL holder flying a non-pressurized single at 10,000 ft at night, 2 h into a 3 h flight. You are on your fourth consecutive duty day, with 13 h awake and 5 h sleep. Cabin heat has been on for 30 min because OAT is −8°C. You develop a mild headache, nausea, tingling in the fingertips, and an unusual sense of well-being. You check a pulse oximeter: 97%. You have no supplemental oxygen. The engine exhaust smells normal; the heater uses a shroud around the exhaust. You have 1 h of fuel remaining plus 45 min reserve. Destination is 45 min away with 3,000 ft broken and 10 km visibility; alternate is 20 min away. You feel capable of continuing.
1. What is the most likely cause of the symptoms, and why is the pulse oximeter misleading?
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The most likely cause is carbon monoxide (CO) poisoning from the cabin heater, with fatigue as a contributor. CO binds haemoglobin much more readily than oxygen, reducing oxygen delivery to tissues. Headache, nausea, tingling and euphoria are consistent with CO exposure.
The pulse oximeter is misleading because standard units cannot distinguish carboxyhaemoglobin from oxyhaemoglobin; a 97% reading can coexist with significant COHb. Altitude hypoxia at 10,000 ft is possible, but the combination of heater use, symptoms and a normal-looking saturation points more to CO. Fatigue from 5 h sleep and 13 h awake worsens judgement and may mask the seriousness of the symptoms.
2. What immediate actions do you take?
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Turn off the cabin heat, open fresh-air vents, and use 100% oxygen if available. Descend below 10,000 ft, preferably to 5,000–6,000 ft, and land as soon as practicable. Advise ATC and request priority. Do not continue to destination.
If oxygen is not available, descent and landing are the treatment. After landing, do not fly; seek medical evaluation and have the exhaust and heater inspected for cracks or leaks. The absence of an exhaust smell does not rule out CO.
3. After descending, the symptoms improve. Can you continue the flight to destination?
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No. Symptom improvement after descent does not prove that CO has cleared or that judgement is normal. CO has a half-life of hours on room air; 100% oxygen shortens it, but medical assessment is still needed. The aircraft heater must be inspected before further flight.
Continuing after a hypoxic or CO event risks recurrence and impaired decision-making, especially at night and after a short sleep. The safe course is to cancel the flight, land, and arrange alternative transport.