Without getting into the middle of this general discussion, I'd like to point out
one thing about RAIM that seems to be misunderstood... One of the primary purposes
of RAIM is 'Predict" when a coverage 'problem' will occur and notify you before it
happens. Now, it can only predict such coverage problems (shortage of sats in view)
based on the orbits and times of the current sat configuration. It may not know if
a specific sat has gone 'out of service'.
Of course, out of service sats and normal coverage shortages are rare these days,
but they do happen. The IFR units will tell you about the upcoming problem BEFORE
it happens, while VFR units will only tell you after it has occurred.
A bigger problem is probably some of the testing that goes on in some locations
which make any GPS unit unusable. Watch those NOTAMs!



Peter wrote:

Jonathan Goodish wrote:


When my hand held Garmin loses enough sats for position calculation, I
receive an alarm on the unit (both visual and audible).


Right, but some of the old units (the 10 year old but still widely
used Garmin 195 being one case that keeps popping up anecdotally)
don't implement this properly.