Pressurised Aircraft Rapid Decompression at FL350
You are at FL350 in a pressurised business jet when you hear a sharp bang from behind the cabin and feel a jolt. The cabin altitude climbs rapidly past 14,000 ft within seconds; the passenger oxygen masks have deployed. The cabin temperature drops sharply and there is a visible mist. Your ears are painful and you feel gas expanding in your abdomen. The first officer reaches for the checklist. Terrain along the route is below 6,000 ft for the next 60 nm, and the nearest airport is 15 minutes away. One passenger is 34 weeks pregnant; another has a fresh dental filling and reports severe tooth pain.
1. Prioritise the immediate actions and explain the physiology behind each.
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The event is an explosive or rapid decompression. Immediate actions in order:
- Oxygen masks on, both pilots, 100 percent, and confirm flow. At FL350 the time of useful consciousness after rapid decompression is roughly 15 to 30 seconds, so mask donning must be a conditioned reflex before any checklist or diagnosis. Hypoxia is the fastest killer here.
- Emergency descent to 10,000 ft or the lowest safe altitude, with speedbrakes and idle power as appropriate, and a turn away from terrain if needed. Terrain below 6,000 ft allows descent below 10,000 ft, which removes the need for passenger oxygen once the cabin is repressurised or the aircraft is low.
- Declare an emergency and request priority, then care for the cabin.
The physiology: the pressure ratio between cabin and outside at FL350 is large, so gas in body cavities expands by roughly the same ratio. Expanding gas in the middle ear and sinuses causes the ear pain, and expanding gas in the gut causes the abdominal discomfort. The mist is water vapour condensing as the cabin cools. The pregnant passenger is at risk from hypoxia and from the physical stress; the dental pain is expansion of trapped gas under a filling, which will resolve as cabin altitude falls.
2. How do you manage the passengers and the choice of destination once the descent is under way?
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Passengers: confirm all masks are being used and that anyone who appears confused is assisted. Do not delay the descent to treat individuals. Once at a safe cabin altitude, remove masks and assess. The pregnant passenger should be given oxygen if there is any doubt about her condition, kept warm, and monitored for breathlessness or abdominal pain; arrange medical assessment on arrival. The dental pain should ease with the descent and needs only reassurance and analgesia if available.
Destination: the nearest airport at 15 minutes is the right choice unless it has inadequate medical or runway facilities. The decompression source is unknown, so the aircraft may not hold cabin altitude and a second descent may be needed; a short diversion to a field with emergency services is preferable to continuing. Consider the passenger with abdominal pain and the pregnant passenger when choosing between two nearby fields, and request medical support on arrival.
Do not attempt to troubleshoot the pressurisation system before the emergency descent is established and the crew are on oxygen. Structural damage is possible after an explosive event, so handle gently and avoid high manoeuvring loads.