On Fri, 24 Nov 2006 22:00:24 -0700, "Mike Noel"
wrote:

This is probably something best left to someone with experience to avoid the
frustration of making interacting adjustments until you get it right. I had
the avionics tech do it for me at my last annual. He used test tools to
generate a magnetic field instead of actually taking the plane out onto a
compass rose on the ramp. The guy did a superb job.


I have never heard of that method being used, but in principle, I don't like
it! It is always best to calibrate something under the same conditions in
which it will be used. Simulating the earth's magnetic field is just adding
one more approximation to the calibration.

First: Just how did your avionics tech align the generated field with the
airplanes longitudinal axis? How accurately? How could you tell?

Second: How did the tech adjust the generated field to be the same strength
as the earth's magnetic field? It would have to be, or the compass
ajustments will not be correct.

Third: How did your tech eliminate the earth's magnetic field from
influencing the compass during the swinging? Seems your compass was
compensated in the presence of two magnetic fields -- one of which won't be
there when you are flying.

I'm more than a little suspicious about the technique.