In article ,
"Bob Chilcoat" wrote:

Recently one of my partners reported that the compass (standard whiskey
compass, not a vertical card) on our Archer was reading 20-25 degrees off of
runway heading at departure. Today a new partner was up with an instructor
for his sign off and reported the same thing. I hadn't noticed, but we seem
to have a definite problem. Nothing has changed in the plane for a long
time. We recently replaced the old Garmin GPS with a Lowrance AirMap 300
(which has its antenna on the top of the glare shield near the compass), but
the first incident was before that substitution was made. Any idea how
something like this can happen?

--
Bob (Chief Pilot, White Knuckle Airways)




There are two basic possibilities:

1) Something is wrong with the compass. Things that can go wrong with
compasses include leaking fluid, worn or damaged bearings, or somebody
twiddling with the conmpensation magnets.

2) Something changed in the environment the compass operates in. The
aircraft has its own magnetic field. What the compass senses is the
(vector) sum of the Earth's field and the aircraft's field (this is what
the compensating magnets compensate for). If you've had equipment
installed or removed, or wires re-routed, this could cause the problem.

Note that "installed" doesn't mean it's got to be bolted in. If it's in
the plane, it'll affect things. Maybe your partner is carrying
something in his flight bag that might affect things?