Re: Rate of climb and descent

Date:         19 Feb 98 01:34:39 
From:         "Marv Woolard" <>
Organization: Flashnet Communications,
References:   1 2 3
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jf mezei <"[non-spam]jfmezei"> wrote in article <airliners.1998.300@ohare.Chicago.COM>...
> Is there a "passenger comfort" component in limiting the rate of descent
> of any aircraft ? I am thinking in terms of cabin pressure change rate
> during descent which can cause quite a bit of pain in ears if it is too
> fast.
> DOes this rate vary according to aircrtaft type ?
> (eg: DC-9 seems to have poor pressure controls so its rate of descent
> 	  would be more limited than a 747 for instance).

Older types may not have as sophisticated systems.  Electronic
controllers generally do a good job limiting cabin rates of descent.
Most have a rate knob which permits operator intervention (ie pilot) to
increase or decrease programmed rate.  The normal rates are 500 fpm in
climb and 300 fpm in descent in most types that I've seen; these are
adjustable within a small range (like 1000 fpm climb to 500 fpm
descent).  The real problem with fast descents is that the cabin can
become depressurized prematurely; most plan depressurization just before
or after touchdown (so the pilot presets Landing Field Elevation so that
the controller knows to which altitude to descend) and in most cases the
cabin pressure altitude is equal to the landing field elevation 2-3
thousand feet above the airport elevation.  In steep, uninterrupted
descent you could end up with the cabin altitude at 2,000 feet when the
aircraft reaches 2,000 feet; ergo depressurized and then the rate of
descent of the cabin will equal the rate of the aircraft (probably
greater than the programmed 300 fpm, programmed rate).  Normal descent
profiles do not result in this!