PPRuNe Forums - View Single Post - Uncontrollable Cabin Pressurisation B737NG
Old 21st Oct 2018, 01:20
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Tee Emm
 
Join Date: Jun 2006
Location: Australia
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Long story short, take your time....
Sound advice indeed. The majority of simulator exercises involving a depressurisation problem seem to be a rapid depressurisation scenario where everything is rushed as a matter of dire urgency. This can lead to a bit of a trap in that if the actual problem in the real aircraft is nothing more than an uncommanded pressurisation change, rather than a obvious rapid decompression requiring an emergency descent, there may be a tendency for the crew to revert to their simulator experience and get going down fast without first evaluating the real problem. Been there done that in a 737-200 in the middle of the night over the South Pacific ocean.

In our case, the first indication was a cabin altitude warning horn as the cabin altitude climbed through 10,000 feet as we were climbing through 31,000 feet. The warning caught us completely by surprise as there was no ear distress.

In those days, the Boeing SOP required the captain to take over control, call the drills aloud and among other things call for the F/O to close the outflow valve. In the meantime I commenced the emergency descent even though the initial cabin rate of climb was less than 1500 fpm. It turned out later the problem was a faulty pressure controller. The closing of the outflow valve was the killer for our ears and the ear pain was very bad during the rapid descent. It was only when I realised I had cocked up the diagnosis (which I conveniently blamed afterwards on poor simulator training in that everything was rush-rush-rush), that I saw the cabin altitude had gone from circa 12,000 feet to 3000 feet in under 90 seconds. That's what happens when you close the outflow valve fully when there was no need to.
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