a problem with compass swing

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photofly
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a problem with compass swing

#1 Post by photofly » Thu Sep 14, 2017 4:20 pm

I'm having trouble with my compass. With the aircraft aligned magnetic north, the compass is adjusted to read 360. Then with the aircraft aligned south, the magnetic compass reads 150 degrees, 30 degrees off. That's twenty degrees too much error to pass.

With the compass on my bench I have no such issue, there's only about five degrees error between N and S.

So I conclude the aircraft steel parts in the vicinity of the instrument panel have too much residual magnetism. Is that likely to be the explanation? Any ideas how to improve things?
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cgzro
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Re: a problem with compass swing

#2 Post by cgzro » Thu Sep 14, 2017 5:45 pm

Yup- The compas has little adjustable magnets in it and a procedure for compensating by moving the magnets around. Also make sure the electronics are turned on and dont use magnetic screwdrives anywhere near the compas. Real pain.

Also possible to degauss but ugh
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Re: a problem with compass swing

#3 Post by photofly » Thu Sep 14, 2017 6:09 pm

The magnets will centre the error, but 30 degrees between north and south would mean the corrections would be +15° and -15° which is beyond the allowed value.

Any ideas about degaussing?
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Re: a problem with compass swing

#4 Post by GyvAir » Thu Sep 14, 2017 6:46 pm

Is the aircraft new to you? If not, was anything changed recently? Windshield retaining screws driven with a magnetic driver can be close enough to influence things a bit.

If you haven't already, try verifying that the compensator magnets are both moving properly and set to neutral, then try another swing from scratch. I trust you’ve verified it’s full of fluid, if applicable.
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Re: a problem with compass swing

#5 Post by photofly » Thu Sep 14, 2017 7:25 pm

GyvAir wrote:Is the aircraft new to you? If not, was anything changed recently? Windshield retaining screws driven with a magnetic driver can be close enough to influence things a bit.

If you haven't already, try verifying that the compensator magnets are both moving properly and set to neutral, then try another swing from scratch. I trust you’ve verified it’s full of fluid, if applicable.
The airplane is new to me... I'm slowly working my way through the inevitable list of squawks. Random compass headings in flight is just one of them :-)

The compass is not brim full of fluid, but the cup floats freely. I will be topping it up when I find something suitable.
I'm also going to try relocating it.
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Re: a problem with compass swing

#6 Post by GyvAir » Thu Sep 14, 2017 7:48 pm

Good luck! It can be a frustrating search for the culprit, sometimes.
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Re: a problem with compass swing

#7 Post by helicopterray » Thu Sep 14, 2017 10:43 pm

Check that the compass mounting screws are brass or stainless, and not steel screws. Or steel screws spray painted black...
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Re: a problem with compass swing

#8 Post by who me ? » Fri Sep 15, 2017 6:25 am

confirm ,
that you are using a Brass screwdriver ? not a steel screwdriver ?
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Re: a problem with compass swing

#9 Post by DonutHole » Sat Sep 16, 2017 8:06 am

Good, they finally added compass swing to 625 app a
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Re: a problem with compass swing

#10 Post by robertw » Mon Sep 18, 2017 7:18 am

DonutHole wrote:Good, they finally added compass swing to 625 app a
Ummm... Really? Where?

I just read through the list of elementary work 3 times and did not see anything related to the compass anywhere.
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Re: a problem with compass swing

#11 Post by photofly » Mon Sep 18, 2017 7:45 am

Actually it was an AME who was unable to get the compass to line up. Donuthole can rest assured that his brethren were being well compensated for their time.
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Re: a problem with compass swing

#12 Post by gwagen » Mon Sep 18, 2017 1:04 pm

What kind of airplane?
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Re: a problem with compass swing

#13 Post by gwagen » Mon Sep 18, 2017 1:16 pm

Maybe you could use an old handheld cassette tape degausser?

https://www.amazon.com/RADIO-SHACK-POWE ... B000T9ZEK8

Cheap to try anyways.

I used to use a desktop one at a radio station. Trick is to slowly pull the tape away from the degausser or likewise the degausser from what you are trying to demagnetize.
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Re: a problem with compass swing

#14 Post by DonutHole » Mon Sep 18, 2017 7:01 pm

photofly wrote:Actually it was an AME who was unable to get the compass to line up. Donuthole can rest assured that his brethren were being well compensated for their time.
Is it possible the compass is fucked?

Usually when I can't get it to line up I just replace it with one that works.
robertw wrote:
DonutHole wrote:Good, they finally added compass swing to 625 app a
Ummm... Really? Where?

I just read through the list of elementary work 3 times and did not see anything related to the compass anywhere.
Lol *shakes head*
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Re: a problem with compass swing

#15 Post by DonutHole » Mon Sep 18, 2017 7:04 pm

Photo.

Seriously though. You're not the kind of guy that's going to use an ame who doesn't know how to swing a compass. From what I know of the you you present out here I can see you probably wouldn't suffer a fool.

They know how to do it properly, you know how to do it properly... If it doesn't work it's the instrument or the earth... So.. which one of those can you fix?
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Re: a problem with compass swing

#16 Post by photofly » Mon Sep 18, 2017 7:33 pm

I asked my AME guy to look at it briefly, at the end of a long day working on other stuff. With the equipment available it was fairly clear there was a big error. He suggested cutting our losses and buying a new compass. They're about $200, so that's not the worst outcome, but when removed from the airplane this compass doesn't seem so bad so perhaps a new compass will have the errors when installed in the same place in the same way.

I had a close look at the mounting hardware, and although the nuts and bolts are brass, there were steel washers used, which are now removed. Also the location is on top of the panel, not higher up the windshield, so there may be some stray magnetic fields from hardware there.

It's not clear where to apply a degausser - pretty much everything in the vicinity is aluminium. Again, there's more work for me to do going around with a magnet on a stick checking, to be sure.

i just want to do a bit of checking myself, before buying a replacement, and I appreciate everyone's suggestions.
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Re: a problem with compass swing

#17 Post by robertw » Tue Sep 19, 2017 7:22 am

DonutHole wrote:
robertw wrote:
DonutHole wrote:Good, they finally added compass swing to 625 app a
Ummm... Really? Where?

I just read through the list of elementary work 3 times and did not see anything related to the compass anywhere.
Lol *shakes head*
Ah... I see. That was tongue in cheek. Humor on a forum is sometimes hard to detect for me... :oops:
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Re: a problem with compass swing

#18 Post by Broken Slinky » Tue Sep 19, 2017 8:51 am

Was the compass swing performed on the ground with the aircraft near the same location each time? Did you try it in the air?
I had one that was just out of tolerance on the ground but in the air was fine. Ended up being something magnetic located where we were doing the swing on the ground.
Other compasses checked fine but this one was just more sensitive I guess?
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Re: a problem with compass swing

#19 Post by groncher » Tue Sep 19, 2017 1:10 pm

Is there any way you might be able to try another compass from a different aircraft, before buying a new one?
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Re: a problem with compass swing

#20 Post by digits_ » Tue Sep 19, 2017 1:19 pm

Does it make a difference when the radio/battery master is on/off?

Does it make a difference if you physically unhook the battery? It shouldn't, but at least takes all the power out of the trouble shooting.

How often did you test it? Was there a cell phone or other powered equipment in the plane somewhere? Is there a tool hidden/forgotten in the dash (magnetic screwdriver - like things)?
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Re: a problem with compass swing

#21 Post by GyvAir » Tue Sep 19, 2017 5:41 pm

I find it interesting that in an age of navigation technology that has made the lowly whisky compass almost a thing of the past (I think it is a thing of the past is some newer model aircraft with enough other redundancies built in), the FAA comes out with a new AC just last month, on how to swing a compass.

I see they say that one can use the GPS in flight, as long as the variation can be determined within 0.2 degrees. I still don’t know how one can know, in flight, if their heading and track are the same within 0.2 degrees at any given time.

https://www.faa.gov/documentLibrary/med ... 43-215.pdf
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Re: a problem with compass swing

#22 Post by flyguy73 » Tue Sep 26, 2017 6:50 am

I've noticed that some hand-held devices (specifically a Garmin Aera 500 series GPS) contains a speaker (hence a magnet) and this affected my compass reading significantly. Moving the GPS helped, but in the end, I ended up pitching it and stuck with a Garmin 396 instead.
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Re: a problem with compass swing

#23 Post by AirFrame » Wed Sep 27, 2017 6:22 am

flyguy73 wrote:I've noticed that some hand-held devices (specifically a Garmin Aera 500 series GPS) contains a speaker (hence a magnet) and this affected my compass reading significantly. Moving the GPS helped, but in the end, I ended up pitching it and stuck with a Garmin 396 instead.
The irony, you're forced to forego more modern technology (the Aera) to make antiquated technology work (the compass). The better solution is to remote mount a magnetometer, put a Dynon or Garmin glass panel on the dash, and toss the whiskey compass into the scrap bin of history.

When flying most of us have a backup magnetic compass and GPS in our cell phone anyway. And sometimes a backup backup in our tablets. Regulations haven't caught up with technology, that's all.
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Re: a problem with compass swing

#24 Post by Heliian » Thu Sep 28, 2017 9:42 am

We have a compass cross check system that replaces the requirement for annual compass swings, just like the big jets.

Every certificated aircraft must have an independent standby indicator in case of electrical failure. It doesn't matter how many iPads you have, or gps's.

The whiskey compass is not going anywhere.
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Re: a problem with compass swing

#25 Post by GyvAir » Thu Sep 28, 2017 6:30 pm

No wet compass there:

Image
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