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trafficinsight · December 11th, 2007, 12:38

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.

December 11th, 2007, 12:38	#4
trafficinsight Junior Member Join Date: May 2007 Location: RHV USA! Posts: 171	Re: Mag compass swinging 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.