Re: DC-9 hole

Date:         23 Apr 97 02:58:14 
From:         Seth Dillon <>
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McElravy wrote:
> On the last discussion of "stupid DC-9 tricks" (we were picking on Air
> Canada I believe) someone asked what the hole in the base of the fin was
> for. The question was never answered and I forgot on it until I had
> occasion to fly on a few (NW) over Easter. As I was sitting in the gate
> area I noticed the hole and remembered the discussion.

The hole at the base of the vert, stab on a DC-9 is a ram air inlet for
cooling air for the a/c pack heat exchangers.  There is also a pair of
fans.  If i remember correctly the right pack fan draws air from the
inside of the area aft of the p-dome and the left pack draws air in from
outside.  When ram air pressure is sufficient to overcome fan pressure in
the plenum then a flapper door opens allowing this air to flow.  The APU
inlet is in the bottom of the area aft of the p-dome.  I can not for the
life of me remember where the rudder travel limiter gets its airspeed
input on the DC-9.


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