Flushed Face at FL290: Recognising a Slow Decompression
A two-pilot business jet is level at FL290, 2 h into a 3 h night flight. It is the third night sector of the rotation; both pilots were on duty until 02:00 local the previous night and reported at 20:00 for this leg. About 30 minutes after level-off the first officer notices the captain, who is PF, has become unusually talkative and is repeating a remark about next month's roster. He then reads back a frequency incorrectly twice; asked for the cabin altitude, he stares at the pressurisation panel and says 'it's fine'. His face is flushed and he has begun to unclip his harness. There was no bang and no cabin altitude warning. The cabin rate-of-climb indicator shows +900 ft/min, the cabin altitude is 11,800 ft and rising, and the outflow valve position indicator shows progressively more open. The pressurisation controller is in AUTO and the first officer feels alert and normal.
1. What is happening, and why is the captain's behaviour so easily misread?
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This is a slow decompression, most likely through a failed or stuck outflow valve or its controller: the cabin is climbing at about 900 ft/min, is already at 11,800 ft and will pass 14,000 ft in roughly two and a half minutes.
At FL290 the time of useful consciousness after a sudden loss of pressure is roughly three to five minutes. This is not sudden. The captain has been mildly hypoxic for several minutes already, which means his judgement, self-monitoring, speech and readback have degraded gradually while his subjective impression remains 'I'm fine' - often with euphoria, talkativeness and poor task focus. The flushed face, harness fidgeting, repeated remark and failure to scan the panel are textbook early hypoxia.
The trap is the plausible wrong explanation: third consecutive night sector, a short rest after a 02:00 finish, and an tired colleague who is behaving oddly. Fatigue is a perfect cover story for hypoxia, and hypoxia is the great imitator. The captain is both the least able person on the aircraft to diagnose himself and the one flying it. The only reliable test is oxygen plus a cabin altitude check, not an opinion.
2. Set out your immediate actions in order and what you would transmit to ATC.
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- Oxygen on yourself first. Mask on, 100 per cent, emergency pressure if fitted. Do not spend seconds verifying the other pilot before securing your own supply; if you both become hypoxic there is no one left.
- Oxygen on the captain. Mask on, microphone selected, intercom confirmed. Expect resistance or confusion; hypoxic crew have been known to fight off the mask.
- Take control and start the emergency descent to 10,000 ft or the minimum safe altitude, whichever is higher, at VMO/MMO with speedbrake, and turn clear of terrain if required. Do not wait for a clearance.
- Communicate: 'MAYDAY MAYDAY MAYDAY, decompression, emergency descent FL100, heading (xxx).'
- Cabin: PA to the cabin crew, seat-belt signs on, tell them to use their oxygen.
- Then diagnose the pressurisation: outflow valve to manual and close, controller selection, bleed and pack status. The descent itself reduces the cabin-to-ambient differential, so it is both the treatment and part of the cure.
Priority is oxygen, communicate, descend - never diagnose the valve first or ask ATC first.
3. Once at a safe altitude with the captain on oxygen, how do you handle the rest of the flight and the aftermath?
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The captain may recover within a couple of minutes of breathing oxygen, but headache, drowsiness and impaired concentration can persist, and the hyperventilation that often accompanies the recovery can mimic the original symptoms. He does not resume as PF, and probably does not act as a useful crew member for the remainder of the flight. Keep him on oxygen, and you fly and land the aircraft at the nearest suitable aerodrome - a decompression means land as soon as practicable, with an inspection of the pressurisation system before further flight.
After landing:
- The captain needs a medical assessment, not just a cup of coffee; hypoxia plus a possible rapid cabin altitude change carries a risk of barotrauma and, if the cabin exceeded about 14,000 ft for a period, decompression sickness.
- Make the technical log entry and submit an occurrence report: a pressurisation failure with an emergency descent is a reportable serious incident.
- Feed back to the operator's safety system: not the fatigue itself, which is not the cause here, but the fact that a genuine hypoxia nearly passed as ordinary tiredness. The CRM lesson is to treat unexplained behaviour in a crew member as a physiological emergency until proven otherwise, and to check the cabin altitude before forming an opinion.