View Full Version : Compass Adjustment
john ball
2nd Jun 2010, 13:35
Hi Everyone, I would like to adjust the compass in my aircraft. i think i know the proceedure of flying the four points of the compass, adjusting and then doing it again until it is correct. But i cannot remember which of the two screws to turn first or which one adjusts what ??? i do remember that I have to use a brass or plastic screwdriver. Any thoughts or anyone at Biggin want to come and adjust it with me on a calm day.
172driver
2nd Jun 2010, 15:25
Never done this myself, but I always thought that you 'swing' the compass by moving the a/c on a dedicated stand with the correct compass points marked. Never heard about this being done in flight....
bbrunton
2nd Jun 2010, 16:08
Look what I found!
Aircraft Compass Swing - November 2005 Issue - (Aircraft Maintenance Technology) (http://www.amtonline.com/publication/article.jsp?pubId=1&id=1935)
Bill
Mark 1
2nd Jun 2010, 17:37
The quick way:
Line aircraft up accurately to N using an external (landing) compass or marked grid. Make sure you are well clear of steel structures etc.
Turn on all normal flight electrics, strobes etc.
Zero error with N/S adjustment screw (and non-magnetic screwdriver).
Align on S
Adjust to halve error using N/S screw.
Align on E and zero error using E/W screw
Align on W and halve the error using E/W screw.
Do complete swing through 30 degree steps and record deviations (which should now be minimised).
Unless you are on PtF this should be signed off by a licensed engineer or ATPL.
BackPacker
2nd Jun 2010, 20:10
Turn on all normal flight electrics, strobes etc.
Engine too.
With a GA single, this is easily a job for three persons. One in the aircraft to safeguard the controls and to note the deviations/adjust the compass screws, a second one to haul the aircraft around, and a third one some way away from the aircraft with a handheld compass to make sure it's pointing in the right direction.
A and C
2nd Jun 2010, 20:12
Is this a PFA type ? or have you got compass swinging on your EASA maintenance licence? if the aircraft is american registered do you have an A & P ? Do you have a landing compass? will this result in you getting lost?
A lot of questions I know but is this not best supervised by someone who knows what they are doing?
bbrunton
3rd Jun 2010, 02:37
I also recommend making several correction cards.
Like:
Everyhing on - normal operation
Just one radio on - you know, generator / alternator failure trying to get somewhere on battery alone.
Nothing on - you know - the battery ran down in the case above and you are trying to dead reacon home.
Also don't forget, if you are flying an airplane with a manually adjusted Directional Gyro.
CH +/- Deviation = MH
So when you are setting the DG apply the compass correction card before setting the DG.
Bil
“Unless you are on PtF this should be signed off by a licensed engineer or ATPL.”
If you are on a PtF it would need it to be signed off by an LAA inspector.
An untrained person can do it right (I did), but take your time and get at least one preferably two helpers. I used a hiking compass as my landing compass, which worked ok. Some time later I fitted a magnetometer based system (in addition to the classical one). The calibration on this was more straightforward. Both are in fairly close agreement and both work ok in the air.
Rod1
One can set the compass in cruise, from GPS tracks.
In zero wind, it is obvious - the GPS track is your heading. And one can establish the wind easily by flying multiple headings at a constant power setting. Having got the wind, one can fly a GPS track which will correspond to some heading.
This would be much more realistic because one is doing it in cruise power with all avionics etc appropriately powered up and radiating their normal cruise magnetic fields.
At reasonable speeds, say 100-150kt, a light wind, more or less aligned on one's track, will make virtually no difference to just using the GPS track straight off.
The actual compass adjustment procedure is iterative. And one needs a brass screwdriver.
Pilot DAR
3rd Jun 2010, 14:16
An untrained person can do it right
Perhaps, but it still is a maintenance activity, and might require a qualified maintainer to make a maintenance release for the adjustment, depending upon the aircraft...
In Canada adjusting a compass on a certified aircraft requires a maintenance release from a qualified maintainer.
I think that's true everywhere that this is outside pilot privileges, but sadly my vertical card compass (which has always had an impressive correction card with all deviations 1 degree or less) has never been better than five or ten degrees in real flight.
Needless to say that has been corrected now ...
“And one needs a brass screwdriver.”
And there I was using a plastic one…:)
“qualified maintainer to make a maintenance release for the adjustment,”
The equivalent of a release to flight signature from an LAA inspector, but he just has to sign for it, not do the work. I was under the impression that under the old M3 system the compass was swung by the lads and signed off by their boss, who was normally the one qualified person?
Rod1
under the old M3 system the compass was swung by the lads and signed off by their boss, who was normally the one qualified person?
That is how most maintenance is done today, EASA 145 or not :)
john ball
4th Jun 2010, 13:39
Thanks to all of you for the advice. I am going to try it in the air with the GPS and keep flying the points of the compass until it is right. Problem with doing it on the ground is that it should be done with the engine running, but the aircraft is an RV6 taildragger, so not possible to put up on tressles to the flying position !! I did it that way many years ago in a Taildragger Robin DR221 but had forgotten the proceedure until you all reminded me --- thanks
Pilot DAR
4th Jun 2010, 17:37
I was under the impression that under the old M3 system the compass was swung by the lads and signed off by their boss, who was normally the one qualified person?
Well, yes... But there is the trust that the boss was supervising the work to his satisfaction. If the owner/pilot wishes to arrange with the signing maintainer that he does the work, and the maintainer signs for it, because it was properly supervised, that's perfectly fine.
If you do end up doing it on the ground don't do it on concrete unless it is an approved compass base. It may have steel reinforcing rods in it otherwise and give wrong results.