Tell ATC that you aren't 200' low, they're 200' too high (Actually,
I've encountered 200' differences when switched to a new ATC sector -
somebody's not calibrated.)

Seriously, if you set your altimeter to the local AWOS/ATIS/ASOS does it
read the published field elevation? If not, the altimeter needs
calibration. If so, it's not the instrument.

Presumably, it's not the encoder if it passes the bi-annual field check but
do you know if your avionics shop has calibrated their transponder checking
equipment?

When was the last pitot/static check done? Do you have a leak in the static
tubing? If there is a leak in the static system, the altimeter may be
reading cabin pressure which 'could' be higher than a true static.

Oh the fun of chasing gremlins...

Bill Daniels

"Kyle Boatright" wrote in message
...
I was using Flight Following yesterday and was reminded of a problem that
my RV has displayed for a long time: The transponder and altimeter do not
agree. In general, ATC sees my altitude as about 200' lower than what is
shown on my altimeter.

A couple of facts:

- The transponder/encoder always pass their certification checks.

- The pitot/static system is installed per plans.

Any thoughts?

KB