It's possible that something got magnetized during a lightening
strike. Happens
in Mooneys where that 4130 chromealloy tube runs down the center of
the
windshield.

You should check it on cardinal headings with the compensator magnets
completely removed. Should not be off more than about 15 degrees.

I've heard that stronger compensation magnets are available. I think
it would
be better to find the source of interference, as tweeking it that far
will cause
errors on some headings.

BTW, a great way to compensate compasses: On a large part of a ramp,
taxiing
with everything running... Use the track info on the GPS--which is
calibrated in
magnetic heading--to line up on a cardinal heading. Taxi on the
cardinal heading
and smoothly come to a stop without changing the heading -- which can
be
verified by the DG. Much more accurate than lining up on a compass
rose.
Best done with someone along who can make sure you don't run into
anything!!
Best done on some ramp that isn't loaded with steel.

Bill Hale BPPP instructor a&p


On Apr 12, 8:22*am, Stealth Pilot
wrote:
On Fri, 11 Apr 2008 19:45:50 -0700, Road Dog
wrote:





I took my Piper Warrior in for its annual and the mechanic
said that the compass card was missing and that he'd have
to swing the plane to generate a new one.

After swinging it, he claimed that he couldn't get the
E-W deviation within the minimum. So he suggested we
try "mu" shield (or something) to block the source of
magnetism which he claims is coming from one of the
instruments. (He says the compass works fine outside
the plane.)

Note: The instruments are all original, stock. Nothing
has been changed (except a radio was added which he says
is not the source.)

The mu shield fails too. He says the next thing to try is
to move the compass up to between the visors.

He says he has spent 3 hours on this so far. I'm beginning to
wonder, shouldn't a mechanic be able calibrate a compass
in a stock Piper after 3 hours ? Is he incompetent ?
Padding the bill ? Or does this really take this long ?

He has inspected and fixed everything else. Do you think
its reasonable at this time to ask him to sign off
everything else, and take the plane somewhere else where,
presumably, they know how to calibrate a compass ?

the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.
swinging a compass takes about 15 minutes.- Hide quoted text -

- Show quoted text -