Re: B 737-500 Depressurization Incident

Date:         11 Mar 99 03:54:07 
From:         James Matthew Weber <jmweber@goodnet.com>
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>My problem is - how do you express negative cabin pressure altitudes
>since the cabin pressure was definitely below sea level when the a/c
>reached 5,000 ft. As far as I know all the pressure equations are based
>on altitudes of sea level and above. Negative altitudes are not a
>reality of life, are they?

They certainly ARE a fact of life. I carry a pocket altimeter, and I don't
think you can takeoff in most pressurized aircraft without doing so, but
you have to be close to sea level before you can get a below sea level
altitude. The aircraft is usually pressurized at the start of, or just
before, the takeoff roll. That way you discover if all the hatches were
closed and door seals
are OK BEFORE takeoff. Much less painful to discover the airplane won't
pressurize while it is still on the ground.

Usually the cabin altitude drops 100 feet or so below actual altitude,
although I have been in some Airbuses and some very old 727's that went a
lot further than that...
James Matthew Weber  1 602 315 6520   Fax 1 602 638 1316
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