Magnetized airframe affecting compass?

J

jwhopp

New member
We bought a 1979 7ECA last summer. It was pristine! Recently recovered, fancy G5 AI and Garmin Aero VFR GPS. We love it.

But, we discovered the mag compass is up to 40 degrees off on some headings in flight. Replaced the compass, tried swinging it, no luck. Mechanic says the airframe is magnetized and the only solution is to de-gauss it, which is apparently somewhat of a black art.

Does anyone have *experience* dealing with this problem? We use the airplane for flight instruction and checkrides, so we need the compass to be usable for pilotage.

Thanks,

Jim Hopp
 
Is the compass a vertical card compass? They sometimes need compensation balls added.

I do remember the avionics shop commenting that they had to degauss a small section in the tail when installing the AHRS for an Aspen. It was a small area unlike trying to degaussing the cabin of your Decathlon.

I assume you have also checked your compass with the avionics turned off to eliminate that possibility.

Bill
 
I tried to degauss my Super Viking several times.
It worked every time...
Until I cranked it up again! :shock:
Apparently the problem was created by the battery ground itself at crank-up time.

It turned into an exercise in futility. :roll:

At the end I "fixed it" by installing a SIRS compass:
https://www.aircraftspruce.com/catalog/inpages/sirs_compass2.php
 
Thanks @kitepilot @wpbarnar. Yes, we've checked it with avionics off. The mechanic showed me that a new compass would swing toward the airplane when he approached the engine.

We did find a shop in KS that does industrial de-magnetizing. They say they've had success degaussing aircraft.

ACA says they've done it in the past.

I'll post an update with what we learn.
 
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