Peter wrote:
question is really whether the terrain warning feature works in
Post by PeterEurope.
A lot of GPSs have a "terrain" database i.e. you can view primitive
elevation data. For for terrain warnings this needs to be high
resolution, and the unit needs to have input of the aircraft track and
speed so it can decide whether you are heading for a hill.
The resolution in the Garmin handhelds is certainly adequate for a loss
of situational awareness. Where do you get the idea these data need to
be "high resolution" (whatever you mean by that)? Even in the best
Honeywell units the terrain is in something like 600 foot square grids.
I certainly wouldn't want to use that level of detail to build an
instrument approach procedure.
Soon after the Henderson NASCAR CFIT last year in Virginia I simulated
it with my Garmin 296 and received ample and valid warnings that would
have easily avoided the crash. I then transferred the track to
electronic 1:24,000 USGS topoquads and found the display to have been
faithful to the terrain on the topoquads to the extent needed to get out
of trouble before it is too late.
Garmin claims the terrain resolution is "10 times" better in the 496
than the 296/396. The photos Garmin has on their web site of the 496
terrain page don't look any better than the 296's.