"Paul Tomblin" wrote in message
...
I have a Garmin 296 with WAAS, and I get WAAS nearly every time when I'm
flying (but not always), but I only seem to get it about half the time
when I'm driving. But I live, fly and drive up near the Canadian border,
so maybe the coverage isn't as good up here.

Yup. Even within the coverage area of WAAS, if you are not directly below
the satellite (or nearly so) you start running into signal blockage due to
the terrain. Here in the Pacific Northwest, where we are both far to the
north of the satellites and also on the eastern/western boundaries of the
coverage), WAAS is essentially unusable on the ground (though it works quite
well in the airplane).

For the curious, here are some web pages with information about where the
satellites are, and what the theoretical coverage is:
http://gpsinformation.net/exe/waas.html
http://gps.faa.gov/programs/waas/for_pilots.htm

I note that they are in the process of adding a new WAAS satellite, and have
for the moment moved the North America coverage somewhat to the west,
leaving the northeasternmost area of the US without WAAS coverage. They say
that by the Fall, the new satellite will be up, restoring coverage.
Presumably everyone will have somewhat better performance after that (and
some of us should probably be getting better performance now).

Pete