From: utzoo!decvax!harpo!npoiv!alice!danny Newsgroups: net.aviation Title: Re: IFR insurance low cost Article-I.D.: alice.1420 Posted: Wed Jan 26 12:46:04 1983 Received: Fri Jan 28 21:30:11 1983 References: ihuxr.295 avsdT.271 ihuxa.180 alice.1418 ihuxa.182 I certainly agree with Jeff Williams that altimeter failure in flight is not likely (tho I've read about a cupla such incidents). There are several radios/instruments that I would give higher priority to as far as back-ups for IFR flight are concerned. However it is a fact that the altimeter is probably the simplest and cheapest to back up. And considering that we're only talking about accuracy to within a few hundred feet, venting into the cabin is no problem (and having passed the instrument written, we know in which direction it'll be off, right?). I've flown with an (aircraft-type) altimeter sitting in my lap not connected to anything and it agreed with the panel-mounted static-port-vented instrument within about 100 ft. Imagine flying a C172-type aircraft in IMC in an area of 5000' peaks and sufferinf an altimeter failure. Having a back-up that told you your altitude to even within a THOUSAND feet would be highly welcome. (Cabin-venting of course assumes an unpressurized cabin.)