"Maule Driver" wrote:
Yep, this kind of Mode C anomoly happens in ZTL airspace too.
That's one
reason we always go with pilot reported altitude over Mode C
readout.

First time I was called on an inaccurate Mode C by ATL, I took it to
the
shop. They said it was OK and serviced it anyway. ATL called me on
it
again but it's fine everywhere else, almost....

I used to have this trouble westbound through Gulfport's airspace all
the time. It never happened anywhere else and two trips to the shop
didn't help.When I replaced the xponder and encoder with more modern
stuff, the problem disappeared.
--
Dan
C172RG at BFM