Re: Boeing System Enables 747s To Navigate By Satellite

From:         davea@col.hp.com (David E Allen)
Organization: HP Colorado Springs Division
Date:         27 Dec 95 21:43:45 
References:   1 2 3
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Mike (zeus@myth.demon.co.uk) wrote:
: A couple of years ago one of the GPS sats faulted without an error being
: detected for some time (about two days if I remember correctly). This
: resulted in my Uni. ground station (about 60 miles inland) being positioned
: about 80 miles into the North Sea. I would imagine that it has taken this
: long for error detection to become satisfactory.

Just another reason why a vfr gps is not an ifr gps (assuming that your unit
is a "vfr" unit). An ifr unit must calculate positions from all available
satellites and if they don't all agree, it has to say "sorry, no position"
or at least no raim. The vfr (or hiking or marine) units can just ignore
any satellites they don't "like" for the sake of giving a position more of
the time and looking good compared to the competition. (Right - we tend to
judge gps receivers by which one has a position more of the time.) Never
mind whether or not it's a good position. But rest assured - the IFR units
(or 747 units) play by very different rules.

dave allen - Fly because you love it.