Pressurization loss at FL330: descent and crew duties
You are the flight engineer on a three-engine turbojet at FL330. The cabin altitude climbs from 6,000 to 8,200 ft in 3 minutes. The outflow valve position indicator shows nearly closed; both bleed-air pressure gauges read normal; the cabin rate selector is in AUTO. The No. 2 engine bleed was selected off 10 minutes earlier after a bleed trip. Cabin differential pressure is 7.1 psi and decreasing; there is no smoke, and EGT is normal. The captain is unsure whether to continue, descend, or run the checklist. There are 148 passengers and 7 crew; fuel is sufficient for 2 hours. The nearest suitable airport is 25 minutes away with a 9,000-ft runway; terrain is above 10,000 ft along the current route. The aircraft has drop-down oxygen masks.
1. What is the most likely cause, and what is the immediate priority?
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The outflow valve is nearly closed, so a valve stuck open is unlikely. With one bleed already off and the remaining system unable to hold the cabin, the likely causes are a bleed-air leak or duct failure, a pack failure, or insufficient remaining bleed capacity at FL330. Normal bleed-pressure gauges do not rule out a leak downstream of the gauge. The immediate priority is not troubleshooting; it is oxygen and descent. At FL330, time of useful consciousness without oxygen is roughly 30–45 seconds, and the cabin is already at 8,200 ft and climbing about 700 ft/min. I would ensure the oxygen masks are on and communications are established, then descend. The checklist can be run during the descent. Continuing at FL330 while the cabin climbs is the one option that is clearly wrong.
2. How do you divide crew duties during the emergency descent?
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The captain flies and makes the cabin announcement; the first officer handles ATC, requests the descent, and advises the nearest airport; I run the pressurization/oxygen checklist and call cabin altitude, differential pressure, and any smoke or electrical abnormality every 1,000 ft. The cabin crew must confirm masks are on and secure the cabin. I would also confirm the oxygen mask duration and the number of passengers so the captain knows the time available. The coordination point is that someone must own the cabin-altitude callout while someone else flies; otherwise the descent can be level-off at an unsafe cabin altitude. If the cabin altitude continues to climb after the descent begins, the captain needs that information immediately, not after the checklist is complete.
3. What descent target and airport choice do you recommend?
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I would descend to 10,000 ft or the highest terrain/MEA along the escape route, whichever is higher. Terrain is above 10,000 ft on the current route, so a descent to 10,000 ft may not be safe; I would plan 11,000–14,000 ft as required and keep the masks on until the cabin altitude is under control. The nearest suitable airport is 25 minutes away with a 9,000-ft runway, which is a better choice than continuing toward destination with a pressurization problem. I would declare an emergency and request priority. If smoke appears or the cabin altitude cannot be controlled, the descent becomes maximum-rate and the airport choice becomes the nearest runway, not the most convenient one.