Don Hammer wrote:
On larger aircraft they usually call out only non-ferris screws within
about 18" or so, epending on the manufacturer. They are usually in
the wing tips about the same distnce from the nav lights and strobes.
We swing the compasses when done and adjust them for their location.


Those are the easy ones. Nothing like leaning on a speed handle
looking straight down at the ground a dozen feet below. In UH-1P it's
in the boom on the other side of a bulkhead from the access panel on the
bottom of the boom. Compass swings were quite amusing.

Degaussing windscreens in the rain is also fun. As Don said
nonferrous screws are the only ones allowed within a specified radius.
However ferrous metals do wind up close to mag compasses. I found one
aircraft type, I forget which, has the compass light switch right next
to it. You guessed it, it ferrous content. Since it was mounted under
the compensation magnets I don't think it mattered much, but the compass
moved a couple of degrees when the light was turned on.

Dan, U.S. Air Force, retired