Originally Posted by
BOAC
Deep breath time again. Can I request a summary from 'the knowledgeable'?
2) Is it established that we have no ACARS message recording LOSS of cabin pressure AND is it confirmed that the ACARS message we have refers to excessive cabin DESCENT rate?
I don't think it has been established that it was a DESCENT rate. I believe this is simply an advisory of a rate of change either up or down that exceeds a set parameter. It has been said that this parameter is 1800 fpm.
Some are suggesting that due to de-pressurization the cabin vertical rate showed an excessive rate of climb, and others are suggesting a possible excessive rate of descent as the aircraft descended to the sea. Either scenario is possible.
It appears that some people are confused by the fact that the cabin pressure PSI will
decrease as the cabin climbs or that the cabin pressure will
increase as the cabin descends.
In reality the message is only about a simple rate of change in cabin altitude (vertical rate) and at this point it tells us very little.
The cabin altitude could be changing due pressurization at altitude (resulting in a climbing cabin) or it could also mean the cabin was descending below the normal cabin altitude of about 8000' when at cruise. (If the aircraft was in any sort of a dive, the cabin would at some point have to descend below 8,000 feet)