Re: Passenger cabin pressurization

Date:         17 Sep 97 02:49:15 
From:         hmt@cygnus.co.ukx (Hugo Tyson)
Organization: Cygnus Solutions, Cambridge, UK
References:   1 2 3
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In article <airliners.1997.2233@ohare.Chicago.COM> "Robert J. Montgomery" <murdock@ameritech.net> writes:
> Gerard Foley wrote:
> > jf mezei ("[non-spam]jfmezei"@videotron.ca) wrote:
> >
> > : I have seen mentioned often that modern airliners maintain a cabin
> > : pressure of 8000feet when flying at cruise altitude of 30-40k feet.
> >
> > : Is this an urban myth or actual precise figure that applies to all
> > : airliners ?

I have a watch that does pressure and altitude; the lowest pressure I've
ever seen on any flight (UK to US, Japan, Indian Ocean, Africa, and within
Europe) is about 815 millibars.  0.8 atm as a lower bound.  Dunno what
altitude that corresponds to, didn't use that mode. ;-)

I believe there's a differential pressure valve that maintains internal
pressure at a fixed 6 to 8 psi (about 500mB) above outside, the craft is
constantly pumped up by fanned air from the engines to that pressure.

How descent is handled I dunno, another valve to let anything over ambient
out so long as ambient is > 0.9bar absolute, say?  That covers landing at
high airfields and so on...

	- Huge