Good Day All,

My Precision vertical card compass seems to be off about 40 degrees at times. It occured pretty much overnight. There has been no change to the aircraft equipment, nothing added, nothing taken away to the configuration of the aircraft.

Are these vertical card compass units fixable, is there a calibration that can be done, etc.?


Thanks


Macdon221

I don't know much about vertical card except that it had same problems as regular compass. You still have NDB up there. Every military aircraft here has had a RMI for years. They made ADF work a snap. Should be cheaper now, for a rebuilt one. They have both the VOR and ADF needle on the same compass. You actually have situational awareness with VOR. CDI only tells you which side of the radial you are on. I generally shot the VOR approach with the wide #1 needle on the RMI just like NDB approach on the narrow #2 needle. Both always point to their respective stations.

There are N/S & E/W adjustment magnets with screws as you undoubtedly know for small corrections. For larger ones, I have seen these rabbit ears on one aircraft:

http://www.chiefaircraft.com/aircraft/flight-instruments/magnetic-compasses/pcn-pbb475.html

Some aircraft exhibit large discrepancies between engine off and engine on conditions.

The "overnight" aspect seems a mystery to wonder about, though.

macdon221 wrote:Good Day All,

My Precision vertical card compass seems to be off about 40 degrees at times. It occured pretty much overnight. There has been no change to the aircraft equipment, nothing added, nothing taken away to the configuration of the aircraft.

Are these vertical card compass units fixable, is there a calibration that can be done, etc.?


Thanks


Macdon221

Yours isn't the first time I've heard of a Precision vertical card compass going haywire. I don't know if it's fixable, but the stories are why I didn't consider one when it was time to replace my original Airpath. When I realized that I was having to redo the compensation of the compass every few months and it was leaking a bit anyway, I started asking questions. I had considered a vertical compass as being easier to read, but I saw a number of complaints from different sources about failures and inaccuracies, similar to yours.

Someone here suggested the SIRS compass as being reliable. That's what I got (from Aircraft Spruce), and I've been totally satisfied. It still reads backwards like all whiskey compasses, but it's stable, and it hasn't gotten out of whack since it was installed--that's been about 3 years now. I had my IA do the installation, but I did the compensation myself (I've compensated many compasses in boats and vehicles, and a few in airplanes). So if you decide to replace the vertical model you have, I recommend considering the SIRS compass.

Cary

Buy the compensator balls, as posted from Chief (Spruce sells them too). They're cheap and often work.

If that doesn't do it, buy a SIRS compass from Spruce.

MTV