Pressurisation Failure at High Altitude
You are flying a pressurised twin turboprop at FL250 with a cabin altitude of 8,000 ft. Without warning, the cabin altitude climbs rapidly and reaches 14,000 ft. The first officer reaches for the oxygen mask but hesitates, saying he feels fine. You are 60 nautical miles from the nearest suitable airport, which has a 9,000 ft runway and is below you. The aircraft has a 10,000 ft cabin altitude limit for normal operations and a 14,000 ft limit for supplemental oxygen use. Passengers include an infant and an elderly passenger with a cardiac history. The autopilot is engaged and the aircraft is stable.
1. What are your immediate actions and the correct priority order?
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Priority 1: Protect consciousness. Don oxygen masks immediately, both pilots, and establish communications. The first officer's feeling of wellbeing at 14,000 ft is a warning sign, not reassurance: hypoxia produces euphoria and impaired judgement before obvious symptoms. Do not debate it; mask on.
Priority 2: Control the cabin altitude. Select the oxygen masks to the passenger cabin, and initiate a descent. A descent to 10,000 ft or below restores a cabin altitude that does not require supplemental oxygen for everyone. Because the airport is 60 nm away and below you, a descent is both the corrective action and the diversion.
Priority 3: Communicate. Declare an emergency or urgency with ATC, state the cabin altitude and your descent, and request priority to the airport.
Priority 4: Manage the passengers. Cabin crew should ensure masks are on and passengers are briefed. The infant and the cardiac passenger are at higher risk and should be monitored.
Priority 5: Diagnose. Only after the descent is established should you investigate the pressurisation failure, and only if it does not compromise the descent.
2. Why is the first officer's statement that he feels fine a hazard, and how should you handle it?
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The hazard. At 14,000 ft the effective oxygen partial pressure is roughly 60 percent of sea level. Hypoxia at this level causes impaired judgement, reduced coordination and a false sense of wellbeing. A pilot who feels fine may already be making poor decisions. The first officer's hesitation is itself evidence of degraded cognition.
Handling. Give a direct, unambiguous instruction: mask on now. Do not negotiate. Use a challenge-and-response check to confirm the mask is sealed and oxygen is flowing. Assign him a simple, verifiable task, such as reading the cabin altitude and calling it out, so you can assess his performance. If he is slow or confused, take control of the aircraft and the radios yourself.
After the event. Both pilots should be assessed on the ground. Document the exposure time and cabin altitude. Consider that the first officer may not be fit to continue the flight.
3. What should you consider about the destination airport and the passenger situation?
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Airport considerations. The airport has a 9,000 ft runway, which is generous, but you must confirm the approach minima, the runway condition and the weather before committing. A high-altitude airport may require a different approach speed and a longer landing distance. Confirm that emergency services are available and that the airport can handle the passengers.
Passenger considerations. The infant and the elderly cardiac passenger are at higher risk from hypoxia. Ask cabin crew to monitor them and be ready to request medical assistance on arrival. Brief the passengers calmly; panic increases oxygen demand.
Operational considerations. Plan for a possible overweight landing and consider a fuel dump if the aircraft is so equipped and the situation allows. Do not delay the descent to manage paperwork.