In my case, it was a CAVU day but extremely windy and quite turbulent. It
was 25G35 blowing straight down the runway with a 10-15kt shear every now
and then. I was bouncing all over the place on final, and the ground was
going by much more slowly than in a normal 0-15kt headwind. My ASI, VSI, and
altimeter were all not working, the sight picture was constantly changing
due to turbulence, and the rate of ground passage was much slower than on a
normal day, making it difficult to guage anything accurately by sight. It
was nice to be able to know I was nowhere near the stall by adding 25 to my
GPS groundspeed.

The cause of this remains unknown, as it cleared itself up while I was still
about 500'. The symptoms were a non-zero but clearly wrong airspeed (it was
stuck at about 60 kts for a while), a VSI pegged at 1000fpm climb, and a
frozen altimeter.

"Colin W Kingsbury" wrote in message
ink.net...

"dlevy" wrote in message
...
GPS groundspeed implies airspeed. If the airspeed indicator is zero,
rpm's
2500, the nose pitched up, and gps groundspeed holding at 80 knots......
which is wrong?

You see the ground moving and the altitude isn't dropping- no GPS needed


GPS groundspeed isn't really useful for aviating, since you've got to
factor
wind in. 20 knots is the difference between too fast and too slow in
approach. OTOH, if you fly pitch and power settings, you won't come to
grief
no matter what the wind is doing. Even IFR the GPS groundspeed isn't
necessary. If your power is too low you'll lose altitude, too high you'll
climb. I've flown complete approaches in actual IFR with a post-it over
the
ASI, and never once looked at the GPS groundspeed.

So, you don't need the GPS to tell you you're moving, and it can't tell
you
what your airspeed is, while pitch/power will let you fly the plane all
day
long. What does GPS buy me again in this situation?

"Colin W Kingsbury" wrote in message
ink.net...
snip
GPS groundspeed is useless for flying the plane. What do you think
you're
getting by watching it?

-cwk.