How can a compass suddenly go out by 20 degrees?

Thanks for all the suggestions. I went out today and looked at the plane
myself (I had only heard about this via a couple of my partners. Turns out
that someone had riveted a compensation magnet to the windshield post behind
the compass, with a really crumby bracket made from very thin aluminum
sheet. Somehow this had been bent a few tenths out of line, probably by
someone parking their headset on the glare shield. It was obvious that it
was out of position, because you could see where it had originally been by
paint marks. When I pushed it back to near the original position, the
compass swung back to near the correct reading. Unfortunately, now that the
bracket is bent, it will not go back to the original position without being
removed and straightened. Since I don't want to drill out the rivet in 25
degree weather, I duct taped it back into position and will fix it properly
when spring finally gets here. Actually, I think I'll try and swing the
compass without it first, and see if it's really necessary at all.

Next question, can a non-A&P owner swing a compass, or must I have a real
mechanic do it?

BTW, the GPS antenna and cable has no effect on the compass at all, even
when right next to it with the GPS on. I knew the antenna was OK, because
the compass problem was reported before I changed to the glareshield-mounted
AirMap antenna.

Bob (Chief Pilot, White Knuckle Airways)

"Bob Chilcoat" wrote in message
...
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)

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

I see you've already found the problem, but the local soaring club's
Grob has problems with the front-seat compass, and it turned out to be
related to a weld on the cabin-air vent. The mechanic managed to magnatize
it when he was welding it, and the compass swings 20-30 degrees off,
depending on the position of the cabin air vent!

So I'd check things that had been welded on recently.

Tina Marie

Bob Chilcoat wrote:

Next question, can a non-A&P owner swing a compass, or must I have a real
mechanic do it?

You cannot legally adjust the compass unless you belong to Ron Natalie's church. :-)
You can't make up a new official compass card. You *can*, however, swing the
plane through the compass points and find out how bad the situation actually is.
I have also heard of people making up their own unofficial compass card while
leaving the official one in the plane.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

"G.R. Patterson III" wrote in
:

You cannot legally adjust the compass unless you belong to Ron
Natalie's church. :-)

This is, unfortunately, true. Some FSDO's will tell you that even your
A&P/IA can't do it.

You can't make up a new official compass card.

This one is more controversial. I've heard your view. I've also heard
some folks whom I would consider very knowledgable say that you can.
[Barry Schiff has a section of a WWoF tape showing how.] Have you ever
seen anything official (and John Lynch doesn't count G), either way?

Yes, it's not listed in 43.13, but then since you aren't repairing
anything, it wouldn't need to be.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

"G.R. Patterson III" wrote in message ...

You cannot legally adjust the compass unless you belong to Ron Natalie's church. :-)


Hmmm... My compass has a little light inside. Now that light's
wire runs down behind the panel and into the bus. Coincidentally, the
landing light circuit is also on the same bus. Anyone for
troubleshooting a pesky landing light problem?

John Galban=====N4BQ (PA28-180)

Sacramento Sky Ranch rents out a degausser.
kent Felkins






I see you've already found the problem, but the local soaring club's
Grob has problems with the front-seat compass, and it turned out to be
related to a weld on the cabin-air vent. The mechanic managed to
magnatize
it when he was welding it, and the compass swings 20-30 degrees off,
depending on the position of the cabin air vent!

So I'd check things that had been welded on recently.

Tina Marie