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Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!whuxl!whuxlm!harpo!decvax!genrad!panda!talcott!harvard!seismo!hao!noao!terak!doug
From: doug@terak.UUCP (Doug Pardee)
Newsgroups: net.aviation
Subject: Re: Pressure vs Altitude
Message-ID: <463@terak.UUCP>
Date: Mon, 1-Apr-85 12:31:14 EST
Article-I.D.: terak.463
Posted: Mon Apr  1 12:31:14 1985
Date-Received: Wed, 3-Apr-85 03:23:54 EST
References: <1164@druxn.UUCP> <1330@amdahl.UUCP>
Organization: Terak Corporation, Scottsdale, AZ, USA
Lines: 17

> In case of altimeter failure without backup, break glass on MP indicator
> and use it as a substitute altimeter, with the above relationship.

Huh?  Although the Manifold Pressure gauge can indeed provide some
gross altitude info, I don't see how breaking the glass is going to
help.  What you need to do is to get the manifold vacuum to zero,
for example by shutting down the engine and stopping the prop.  With
a non-turbo engine, firewalling the throttle will also bring the
vacuum to near zero (but set your prop to fine pitch first :-)

If you're VFR, looking out the windows will provide a clue as to your
altitude.  If you're IFR, ask Center what your Mode C readout is.
(I presume if you're IFR in a plane with a C/S prop, you've probably
got Mode C).  Besides, you have to tell them about your altimeter
failure anyway...
-- 
Doug Pardee -- Terak Corp. -- !{hao,ihnp4,decvax}!noao!terak!doug