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)

I had a compass problem that ended up coming from the coaxial cable going to the
GPS antenna. The RG-142B coax has a copper-clad steel center conductors and running it
up the center pillar in my Cherokee caused the compass to have an error. If you swapped
your GPS's, this could have happened.

It doesn't have to be a magnet in the area to cause problems... just some magnetic
material (like unmagnetized iron/sheet metal/etc). Might also check any bracketry or
screws that may have been replaced. I know the stock compass mounting screws are usually
brass for that reason.

Basically, if it's not just a broken compass but is truly magnetic
interference, you need to find out *absolutely everything* that changed between when it
worked an when it was off. Even stupid little things can cause the error.

-Cory




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* The prime directive of Linux: *
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