Article 28523 of sci.geo.satellite-nav:
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From: 76703.4321@compuserve.com (Don Curtis)
Newsgroups: sci.geo.satellite-nav
Subject: Re: GPS-89 Glitch
Date: Mon, 02 Dec 96 06:29:21 GMT
Organization: CompuServe Incorporated
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In article <329F47DB.3676@schange.com>, Beat Marti <bmarti@schange.com> wrote:
>Can a GPS reading be trusted???
>
>A few days ago something rather strange happened to me when I flew from
>Amsterdam to Boston. I had turned on my GPS-89 sometime after we took
>off in Amsterdam and got an accurate fix that I verified with the
>in-flight display information regarding speed, altitude and position.
>
>Sometime later, when we were somewhere over Labrador, I turned on the
>GPS-89 again and got a fix with about 6 satellites and good signal.
>To my surprise, the speed and altitude were correct, however, the
>position was way off (longitude only) by about 30 degrees!!! I
>watched it for a while thinking that it would eventually fix itself
>but it happily continued tracking.
>
>I turned off the GPS for a few seconds, turned it back on and got a
>new fix within about 20 seconds, but noticed that the satellite
>constellation took a jump. This time the position was correct.
>
>I am very surprised to find out that it seems to be possible to get
>a completely wrong reading from a GPS while all indications are good.
>I've used the GPS-89 on several flights both north atlantic and cross US
>and I've never seen this problem before or after -- yet it did happen
>once...

Let's see...Amsterdam to Labrador...that's more than 300 miles so the GPS was 
probably a bit confused about where it really was...and due to the altitude of 
the aircraft...it was able to pickup sats that wouldn't normally be visible if 
you were on the ground...and so it really got confused.

Possible????