Compass Correction/Deviation Card

Discussion in 'Avionics and Upgrades' started by JOhnH, May 1, 2019.

  1. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    I just noticed that my Compass card is missing. I know it was there recently, but not actually sure when the last time I paid attention to it was.

    Should the numbers be in the log book? I looked and didn't see it, but there are over 50 years of entries, and many of them are hand written.

    If I can't find the old numbers, can I fill out a new card myself or do I need my A&P to do it?

    If I can do it myself, is there an accepted procedure that doesn't involve a Compass Rose?
     
  2. dmspilot

    dmspilot En-Route

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    Credit goes to Barry Schiff for this procedure: In lieu of a compass rose, look up the exact magnetic heading of the runway and align the aircraft with it, then set the gyroscopic heading indicator to that heading. Turn to cardinal headings in 30° increments and note the deviation with the engine running at a reasonable flight RPM. You can check to make sure the gyro hasn't drifted at the 180° and 360° points.

    Whether a pilot can fill out a compass card legally, I can't tell you, and have not found a convincing answer one way or the other.
     
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  3. kgruber

    kgruber En-Route

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    The fastest, most accurate method is to use your GPS on the ground. A mechanic must sign it off.

    """NOTE: If aircraft is equipped, GPS can be used (allow for deviation) to establish reference headings for compass compensation. This technique will eliminate possible errors caused by gyro precession."""

    http://www.airpathcompass.com/J30/index.php
     
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  4. MauleSkinner

    MauleSkinner Final Approach

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    The fact that it’s not in the list of preventative maintenance items that can be done without A&P supervision/sign off seems pretty convincing to me.
     
  5. bnt83

    bnt83 Final Approach PoA Supporter

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    You can do that but I'd bet it is not anywhere near equivalent to being on a real compass rose that has actually been surveyed and marked in the last 24 months.
     
  6. Bell206

    Bell206 Cleared for Takeoff

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    A mechanic needs to sign it off. As to alternate procedure, yes by using a Master Sight compass which can be rented for a reasonable rate. Most airport compass roses are out of calibration as the earth's mag field has been moving faster than normal. A quick call to the tower will confirm if an airport's rose is calibrated. Keep in mind the mag compass is technically a navigation device and you need to use calibrated test equipment in order to stay within the requirements of Part 43.13. Personally, I've only used a master compass over the past 25 years since it can be used anywhere.
     
  7. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    There are several places that you can down load a blank card, fill it out put it in the holder.
    It is a required placard it must be in place to be airworthy, but the FAA doesn't give a hoot if it is acrurate.
     
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  8. Doug Reid

    Doug Reid Pre-takeoff checklist

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    Make it legible....put it in view of the pilot.

    The only time your compass is presenting accurate information is in level, unaccelerated or decelerated flight.

    Tom is correct in his response...it needs to be in place...accuracy is another matter. The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS.
     
  9. Clip4

    Clip4 En-Route

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    There nothing on the preventative maintenance list that says you can make a copy of an ignition key either, but I am pretty sure I don’t need a mechanic for that.
     
  10. jsstevens

    jsstevens En-Route PoA Supporter

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    What (on the GPS) do you set it to after takeoff? GPS can give you ground track but not heading.
     
    Last edited: May 1, 2019
  11. Bell206

    Bell206 Cleared for Takeoff

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  12. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    If you are taxiing, how much is your heading going to vary from course? ;)

    (assume dry conditions, on ice things can change)
     
  13. jsstevens

    jsstevens En-Route PoA Supporter

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    Taxiing is fair but the post I responded to said he used the compass only to set the DG before takeoff and thereafter set it to the GPS. He neglected to mention he was only taxiing around. o_O
     
  14. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Only when you are doing a complete compass swing and adjusting the compensating magnets.

    To Duplicate the card, NO! put one in place and go fly.
    Your AC says,
    1. PURPOSE OF THIS AC. This advisory circular (AC) describes procedures for calibrating an aircraft magnetic compass
     
  15. kgruber

    kgruber En-Route

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    Taxiing on the ground, track and heading are the same.
     
  16. MauleSkinner

    MauleSkinner Final Approach

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    Is that considered aircraft maintenance?
     
  17. jsstevens

    jsstevens En-Route PoA Supporter

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    Again the post I responded to said he set the DG using the compass just before takeoff and then used the GPS for the rest. It certainly SOUNDS like he uses the GPS in flight.
     
  18. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    How does that work when you have a 25 degree crosswind correction? Might want to rethink that strategy. Course and heading arent the same thing.
     
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  19. jsstevens

    jsstevens En-Route PoA Supporter

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    My point exactly.
     
  20. kgruber

    kgruber En-Route

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    He said that he set his DG to the GPS on the ground and then used the DG to record the compass calibration. The DG would not precess much in the 3 minutes it would take to make 12 turns/readings.
     
  21. Bell206

    Bell206 Cleared for Takeoff

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    That's the point. He's not duplicating the card as he doesn't have the original heading compensation values. And considering those values can be up to +/- 10 degrees off, what numbers would you recommend he put on his card?

    Why not just swing the compass and put the correct values on the card?
     
  22. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    I think you're reading something different than what we are reading. The implication of his post is that after takeoff he sets his DG to the GPS.
     
  23. kgruber

    kgruber En-Route

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    No. The implication is that he records his compass correction card off the DG. I doubt he is an idiot.
     
  24. jsstevens

    jsstevens En-Route PoA Supporter

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    Maybe not but this is what his post says:” The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS.” I’m not sure why he’d say “before takeoff” if he’s only swinging the compass.
     
  25. dmspilot

    dmspilot En-Route

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    It's not an implication. He literally said exactly that he sets his DG to his GPS after takeoff.

    "The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS."

    This thread turned into a real WTF even for POA.
     
  26. FastEddieB

    FastEddieB Final Approach

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    At Copperhill Airport I made a GPS waypoint at the windsock. I then paced off a distance and marked 2 more waypoints that were directly south of that waypoint. Then painted a line between them, to establish a N/S reference, then painted a perpendicular E/W line. Easy to then get the 30° increments.

    Worked well enough on my Sky Arrow. I assume being Experimental there was no issue with rolling my own. I don’t remember the plane being delivered with a compass correction card.
     
  27. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    So he sets his Compass Card after take off? Re-read what he said.
     
  28. weirdjim

    weirdjim En-Route

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    "Why, that card was in there when I bought the airplane..." :cheerswine:

    The compass correction card is an anachronism, a throwback to the days when we drew pencil lines on paper maps and a 3° error would put you into the next county at the end of a 4 hour cross-country. Between VOR, GPS, and the lot of it, NOBODY I know uses that piece of paper for anything but required equipment for a checkride. Nobody gives a damn if it is wildly inaccurate.

    HOWEVER, there was a compass manufacturer named Tate that once put out a batch of compasses with the directions reversed ... west was east, north was south and so on. Which is where we get the saying, "He who has a Tate's is lost."

    Jim
     
    Last edited: May 1, 2019
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  29. Doug Reid

    Doug Reid Pre-takeoff checklist

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    On the ground is correct. I set the DG to the compass on the taxiway in front of my hangar when I start up, and verify with the gps as I taxi to the active runway. I don’t have a vertical card compass...posted in a hurry...but have to admit I enjoyed the attention. Kgruber wins the door prize today !
     
  30. dmspilot

    dmspilot En-Route

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    How do you set it in flight? This combined with your other post implies that you don't ever reset it after takeoff. And the comment about not having a vertical card compass is a non sequitur.

    You wrote something that made no sense and kgruber was more successful at mind reading than the rest of us. No prizes will be given.
     
    Last edited: May 1, 2019
  31. Clip4

    Clip4 En-Route

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    You are duplicating a part. The key comes with the ignition or the ignition / door lock set. If you can’t replace a placard, how can you replace a key.
     
  32. MauleSkinner

    MauleSkinner Final Approach

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    I guess the key needs A&P supervision/signature, then.
     
  33. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Because he is not allowed to do that.

    That is calibrating an aircraft magnetic compass.
    Actually if you nit pick it, that requires a certified Instrument repair shop.
    Now tell me if adjusting the composting magnets is an alteration of the instrument?
    65.81 General privileges and limitations.
    (a) A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments).
    Are you repairing a compass that was wrong, by adjusting it?

    If we are allowed to adjust a compensating magnet assembly, why aren't we allowed to service the fluid level?
     
    Last edited: May 1, 2019
  34. Bell206

    Bell206 Cleared for Takeoff

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    Ha. Are we talking about the FARs or the TARs? Funny, between the FAA guidance I mentioned above and other guidance like AC-43.13-1B all state a mechanic can swing a compass:
    "Certificated airframe mechanics and certificated repair stations (CRS) with the appropriate ratings are authorized to perform a compass swing, which includes adjustment of compass compensators."

    But you are right on the repairs:
    "Repairs or alterations to a compass may only be made by a CRS holding an appropriate instrument or limited instrument rating."
    No.
    I'm from the side an A&P can service a mag compass as it's not a repair or alteration. Kind of like servicing an engine with oil. Can a pilot do that? And does it require a logbook entry like hydraulic fluid servicing?


     
  35. NordicDave

    NordicDave Line Up and Wait

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    For about $80, my local Av shop used a calibrated magnetometer aimed at the spinner centerline of my aircraft with an optical sight as the plane was turned about the compass rose. The magnetometer verified exactly where the plane was pointing and the different in shipboard compass indication was noted.

    For the life of me, I cannot see how someone could calibrate a compass from a compass rose. It's very difficult to know the 1-4º of variation that needs to be documented on the compass card from a painted marking.

    I like an accurate compass card, just incase I ever urgently needed to fly by compass. Just one of my minimums, I'm sure others don't care.

    -David
     
  36. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    I'd like to be able to do the servicing of a compass fluid, but unfortunately that requires opening the instrument.
    You are correct, adjusting any instrument that does not require opening the instrument to do so is simply an adjustment, not a repair. but unfortunately the FAA feels that removing the top plug, and filling the fluid is a repair of an instrument.
     
  37. Lndwarrior

    Lndwarrior Pre-takeoff checklist

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    This post makes my head hurt.

    So glad I don't have to deal with this archaic nonsense in the experimental world.
     
  38. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Have you forgotten there are members here that might have learned some thing?
    I'm sorry your head hearts, But when examined, I'd be scared if I had a head like your's and it didn't hurt. :)
     
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  39. FastEddieB

    FastEddieB Final Approach

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    The way a compass bounces around, and the close spacing of the markings, plus turning and acceleration/deceleration errors, makes exact, exact precision illusory.

    I think I recall that a 1° error means one mile off course over a 60 mile distance. I found this comforting when using a compass and dead reckoning to navigate long over-water legs in the Caribbean - I could be several degrees off and still have confidence that the next island in the chain would still eventually slide into view. Not to mention the inherent inaccuracy of winds aloft forecasts.

    Don’t get me wrong, I’d like my compass to be as accurate as possible. But a few degrees error one way or another is unlikely to be much of an operational factor in real life flying.
     
  40. bnt83

    bnt83 Final Approach PoA Supporter

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    Each mark being 5 degrees, its easy enough to get under 4 via eyeballs. Drive around the compass rose again and its easy to see that it is repeatable. It can be a lot easier with a tech outside helping the driver get lined up, (second tech is SOP where I work)

    Did the same after calibrating a G5 HSI, compass rose works well.

    Without someone actually coming out and testing an area for magnetic disturbances on schedule, I don't see how any tool could be used to calibrate a compass.


    upload_2019-5-2_6-47-8.png
     
    Last edited: May 2, 2019