Hypoxia Suspected on a High-Altitude Transit
You are flying a helicopter at 10,500 ft pressure altitude on a VFR transit across the Hajar mountains. The cabin is unpressurised and the outside air temperature is −5 °C; the cabin heater is on. After 40 minutes, your passenger becomes irritable, then drowsy, and complains of a headache. You feel mildly euphoric and notice your own handwriting on the flight log becoming untidy. The helicopter is on autopilot, fuel is sufficient for 2 h 30 min, and the nearest suitable landing area is a wadi 6 NM ahead. You have a pulse oximeter in the medical kit and a portable oxygen bottle with 15 minutes of supply.
1. Identify the most likely cause of the symptoms and explain the physiological mechanism.
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The symptoms - irritability, drowsiness, headache, euphoria, and deteriorating handwriting - in an unpressurised cabin at 10,500 ft are classic for hypoxia. At 10,500 ft the alveolar oxygen partial pressure is roughly 55–60 mmHg, giving an arterial saturation of about 85–90% in a healthy person. The brain is the most oxygen-sensitive organ, and the first effects are impaired judgement and euphoria, which is dangerous because the pilot may not recognise the problem.
The cabin heater being on raises the possibility of carbon monoxide poisoning from a leaking exhaust, which produces similar symptoms. The pulse oximeter will help: a low SpO2 supports hypoxia, but CO poisoning can give a falsely normal reading. The combination of both crew and passenger being affected, and the onset after 40 minutes, points to either altitude hypoxia or CO. Both require immediate descent and, if available, oxygen.
2. State your immediate actions and the decision you would make regarding the wadi landing area.
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Immediate actions: don oxygen (both pilot and passenger), select 100% if the mask allows, and initiate a descent to below 8000 ft as soon as practicable, consistent with terrain clearance. Turn off the cabin heater to eliminate a CO source. Use the pulse oximeter to monitor SpO2; if it does not improve with oxygen and descent, suspect CO and land as soon as possible.
Decision on the wadi: 6 NM ahead is the nearest suitable landing area. At 100 kt that is under 4 minutes. Given the pilot's own judgement is impaired, the safest course is to descend and land at the wadi, shut down, and reassess. Do not continue the transit while symptomatic. Once on the ground, ventilate the cabin, check the heater and exhaust for leaks, and do not depart until symptoms resolve and the cause is identified. The 15-minute oxygen supply is enough to cover the descent and landing.