On Apr 11, 10:45�pm, 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 ?


Sure you could take it somewhere else and spend the same or more money
for them to tell you the same thing. If your guy is conscientous
enough to notice the compass card is missing he seems pretty good to
me. It is possible for some of the steel parts in the aircraft to
become magnetized either through a lightning strike or even to pick up
magnetism through the ground just from sitting in the same spot in the
same way for years. That is more common on steel tube aircraft than
largely aluminum but is still possible.

I had a similar tough time swinging a compass in a Commander 114 which
has a large steel support bar just above the compass. Couldn't find a
degaussing devise but was able to get more powerful compensating
magnets which took care of the problem but virtually every point had 2
to 8 points of variation instead of the normal 0 to 5 or less. I also
once found an aircraft compass that had no magnets installed!

John Dupre'