Many times. Glitches can occur with their software. My most common
experience was having one controller tell me to turn off the altitude
squawk, being handed off to another sector, asking the new controller if I
should try Mode C again and having no further problems. Don't sweat it. If
they don't like what they are seeing they will ask for verbal altitude
reports.

Bob Gardner

"Hankal" wrote in message
...
Long CX IFR at 7000
Controller comes on "say Altitude" My response "7000" He says you show
300
feet lower and gives me the altimer reading. I confirm. He says "turn off
you
mod C"
I comply.Look at my GPS which is at 7060.
I go down 50 feet the gps stays at 7060. I go up 100 feet the gps stays at
7060.
The controller comes back and says" I think this is due to a cold front in
my
flight area.
15 miles further my GPS altitude goes to 7000. I queery ATC to turn on my
mod
C. He concurs my altitude at 7000.
Request lower for decend for landing. The gps works fine now, ATC is
happy.

HAS ANYONE ELSE EVER EXPERINCED THIS?