Mag compass swinging

[RPJ]

What exactly is involved when an A&P says he will "swing the compass" to get rid of errors? I made a post in the "technical talk" forum titled "mag compass correction" regarding the problem I was having (http://forums.jetcareers.com/technical-talk/56521-mag-compass-correction.html (Mag compass correction?)). The A&P that looked at my airplane said that swinging the compass will correct the problem.

Do you guys have any other suggestions?

[Cessnaflyer]

Have it installed correctly it is the only way to go.

[Berkut]

Originally Posted by RPJ

What exactly is involved when an A&P says he will "swing the compass" to get rid of errors?

A compass swing is a procedure used to compare the aircraft's compass to a known good standard, usually an airport compass rose or portable calibrated compass. The airplane is turned to several different headings, usually every 30 degrees or so, and the difference between what the aircraft's compass reads and the known good heading is noted. Once the errors are known, the compass can be corrected by adjusting small internal compensating magnets. It's usually not possible to compensate for all of the errors, so the rest are noted on the new compass correction card.

Do you guys have any other suggestions?

It's not a big deal at all. Just let them do their thing and go on about your way.

[trafficinsight]

The mechanic will usually taxi your airplane out to the compass rose with a sheet of paper, pen, and a brass screwdriver. I like to use a marshaller as well so that the headings are more accurate.

In every compass there is a compensator, a set of small adjustable magnets that compensate for errors in the actual compass magnet. The two little brass screws labled N-S and E-W are the compensator adjusters. DO NOT MESS WITH THESE EVER.
We had a flight instructor who decided the compass was off and whipped out his screwdriver and promptly stripped the delicate brass gears in the compensator, ruining it.

To swing your compass first the mechanic will put the airplane on a north heading, then adjust the compensator so the compass points north, then he will turn to a south heading and whatever the error is he will split the difference. (that is, adjust it until it points not quite north and not quite south). Then do the same with east and west. After that he just positions the airplane to the cardinal headings and records the compass heading, constructing a new deviation card.

I've only ever had one compass that couldn't be adjusted to within a couple of degrees and that turned out to be because the number 1 CDI was putting out a HUGE magnetic field. New avionics were on the way and that fixed the problem.