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  • astjp2
    started a topic Airpath compass correction instructions.

    Airpath compass correction instructions.

    COMPENSATING INSTRUCTIONS FOR AIRPATH COMPASSES, taken from: https://www.airpathcompass.com/J30/i...n-instructions

    Before attempting to compensate compass, every effort should be made to place the aircraft in simulated flight conditions. Check to see that doors are closed, flaps are in retracted position, throttles set at cruise position, engine(s) operating, and aircraft in a level attitude. All electrical switches, generators, radios, etc., should be in the position they will normally be for navigation flight.



    COMPENSATION
    • 1. Set adjustment screws of compensator on zero. Zero position of adjustment screw is obtained by lining up the dot on the screw with the dot on the compensator frame.
    • 2. Head aircraft on magnetic North heading. Adjust N-S adjustment screw until compass reads exactly North.
    • 3. Head aircraft on magnetic East heading. Adjust E-W adjustment screw until compass reads exactly East.
    • 4. Head aircraft on magnetic South heading. Note the resulting South error. Adjust the N-S adjusting screw until one-half of this error is removed.
    • 5. Head aircraft on magnetic West heading. Note the resulting West error. Adjust the E-W adjusting screw until one-half of this error is removed.
    • 6. Head aircraft in successive magnetic 30-degree headings and record all errors on the deviation card furnished with the compass.



    For satisfactory results, all extraneous magnetism causing over 30-35 degree compass errors should be removed from the aircraft, or the compass should be relocated to a position where uncompensated error does not exceed 30-35 degrees. Use a brass or other non-ferrous material screwdriver when making compensator adjustments.

    Best results can be obtained in actual flight compensation by following the procedure outlined below:
    • A. Set directional gyro from a sectional line or runway. (Allow for magnetic variation to ensure gyro corresponds to magnetic heading)
    • B. Follow procedures 1 through 6 above.
    • C. Re-check directional gyro occasionally for possible precession, and allow for such precession error in recording results on magnetic compass deviation card.



    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.

    For any questions please contact Airpath Instrument Company at the address or phone numbers listed above.



    COMMON COMPENSATION PROBLEMS

    Any time there is a maintenance or repair to your aircraft, it is recommended that the compass be compensated. This is particularly true if there is work associated with the removal of old and/or installation of new equipment in the instrument panel. New radios and relocation of speakers or intercoms could affect the compensation required. New hardware (i.e. screws, nuts, etc.) installed during maintenance can sometimes be the cause of excessive errors if the hardware is steel or magnetic.

    Loose electrical grounds, lighting, or extended periods of parking in North-South alignment on the ramp can lead to the magnetization of the airframe itself. This is often evidenced by excessive uncompensated compass error (more than 30-35 degrees). Engine mounts on single engine aircraft and center windshield posts becoming magnetized can lead to compensation problems. demagnetizing (degaussing) the airframe component or relocating the compass will solve this problem.

    Remember that every aircraft is different. Following the set-up procedures outlined above prior to compensation is important. As stated, in-flight compensation will achieve the best results. Landing gear position can sometimes affect deviation. Other factors to consider are: yoke position, cruise configuration, pilot heat, and de-icing equipment (particularly windshield anti-ice).

    Operators should consider removing any jewelry while compensating compasses. Such things as watches, rings, and eyeglasses can affect the amount of compensation required. If above method does not give satisfactory results, determine the amount of uncompensated error by aligning the reference dots on the compensator adjustment screws and frame or by removing the compensator assembly from the compass. If the uncompensated error is in excess of 30-35 degrees, troubleshoot for magnetization of aircraft components or excessive electrical interference.

  • Robert Lees
    replied
    Originally posted by PA1195 View Post
    Are runway headings less-same-more accurate than a GPS with current database? I bet less.

    Gary
    Magnetic north is moving towards Siberia faster than anticipated. NOAA (USA) and BGS (UK) www.bgs.ac.uk have been monitoring the shift in the iron core of the Earth. The World Magnetic Model (WMM) is being changed, forcing airfields to re-paint runway markings earlier than anticipated.

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  • PA1195
    replied
    I had two VCard compasses that survived but were in airplanes that had a propeller balance done. Anything mechanical like them can surely wear and fail exposed to excessive vibration. My SIRS compass (https://www.sirs.co.uk/aircraft) appeared to work well in my Cub and has good reviews by others for its ability to be compensated.

    Gary

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  • astjp2
    replied
    I have removed 3 vertical compass card compasses for failures and an airpath put in, regular airpaths get removed and repaired and put back in...

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  • PA1195
    replied
    The SIRS compass model and vertical card compasses work better. I've had them and they seem stable and easier to read once calibrated.

    Gary

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  • Ragwing nut
    replied
    As long as the compass points the general direction I'm going, I will be fine. Its not like they sit very still anyways unless you have a vertical card. I have flown from OK to FL in a tcraft with nothing more than a pile of maps and a handheld icom radio. Anytime radio work is done, the radio shop should calibrate the compass. Problem is alot of the airports don't seem to have a compass rose anymore.

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  • PA1195
    replied
    Are runway headings less-same-more accurate than a GPS with current database? I bet less.

    Gary

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  • 3Dreaming
    replied
    Originally posted by PA1195 View Post
    The North Pole is moving and compass variation will be affected. GPS manufacturers are likely updating their database to reflect that change so incorporate any upgrade they offer. I expect airports to comply with their data soon as well as those that supply instrument flying procedures. A GPS confirmation of our compass may be worthwhile until the ground based upgrades to reference points are effected.

    https://www.ngdc.noaa.gov/geomag/WMM/
    https://www.ncei.noaa.gov/news/world...-cycle-release

    Gary
    It is always moving. Our airport is going to be remarked this Summer. One of out runways will change its numbers. The other runway was built in the late 1970's, and had changed its number 10 years later.

    Leave a comment:


  • PA1195
    replied
    The North Pole is moving and compass variation will be affected. GPS manufacturers are likely updating their database to reflect that change so incorporate any upgrade they offer. I expect airports to comply with their data soon as well as those that supply instrument flying procedures. A GPS confirmation of our compass may be worthwhile until the ground based upgrades to reference points are effected.

    https://www.ngdc.noaa.gov/geomag/WMM/
    https://www.ncei.noaa.gov/news/world...-cycle-release

    Gary

    Leave a comment:


  • Hank Jarrett
    replied
    There are ways to accurately calibrate a compass.....and there are the requirements the FAA has for calibrating them. A lot like the requirements for calibrated aircraft scales for weighing a plane. Most electronic bathroom scales (under $20 at WallMart) are more accurate and repeatable than the "approved" scales. safest to use both. If they disagree, put some known weights on each. When I have done it, guess which one turned out to be out of calibration! Remember you want the scale to be accurate close to the weight you will be measuring, NOT at zero! Same for your compass. Do what the FAA regs require, then verify in flight with your GPS or other devices to be sure the compass rose you used was even right. Sometimes even flying over a road is more accurate than a rose that was painted years ago and is no longer accurate. (don't forget to account for wind angle!!!!!)

    Hank

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  • PA1195
    replied
    There's a rumor that some have taxied a plane on wheels and floats and used the GPS track to cal the compass.

    Gary

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  • astjp2
    replied
    Click image for larger version

Name:	Brunton.jpg
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ID:	181378 I bought one of these to do my own compass swings... https://www.brunton.com/products/con...nt=36245970258

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  • PA1195
    replied
    https://www.faa.gov/documentLibrary/.../AC_43-215.pdf
    http://www.faa-aircraft-certificatio...uirements.html

    Seems +-10* is the requirement in these documents REF Part 23. Whether for not CAR Part 23 applies to CAR 4 aircraft is.......?

    For Part 91 ops those aircraft certified under CAR 4 (pre-TCDS 1A9 "flight manual" Taylorcrafts), section 04.05803 says "This instrument shall be properly damped and compensated and shall be located ed where it is least affected by electrical disturbances and magnetic influences."

    For TCDS 1A9 aircraft (Model 19 and newer) Car 3 section 3.758 says: Magnetic direction indicator. A placard shall be installed on or in close proximity to the magnetic direction indicator which contains the calibration of the instrument in a level flight attitude with engine(s) operating and radio receiver(s) on or off (which shall be stated). The calibration readings shall be those to known magnetic headings in not greater than 30-degree increments.

    Gary
    Last edited by PA1195; 02-15-2019, 14:06.

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  • 3Dreaming
    replied
    Originally posted by Robert Lees View Post

    In the UK (for certificated aircraft) it is a requirement to re-calibrate the compass every 4 years (I think). This probably harks back to Amy Johnson / Alcock & Brown* days (look them up) when all they had was a compass, stopwatch and ruler. And occasionally a chart.

    In this modern day & age of ATC, Foreflight, GPS, iPad apps etc, I think it's absolutely ridiculous to require a compass to be calibrated within 3 degrees of accuracy.

    Rob

    * The first pilots to cross the Atlantic
    With the old bubble face compass, I feel lucky if it is within 20.

    Leave a comment:


  • Robert Lees
    replied
    Originally posted by PA1195 View Post
    What can happen is a lack of periodic calibration of the compass as reflected by the correction card. I do it annually but even then changing cockpit contents can affect the indications. I've never understood the requirement for having a calibration card available without a similar requirement to periodically insure its accuracy. Just me I guess.

    Gary
    In the UK (for certificated aircraft) it is a requirement to re-calibrate the compass every 4 years (I think). This probably harks back to Amy Johnson / Alcock & Brown* days (look them up) when all they had was a compass, stopwatch and ruler. And occasionally a chart.

    In this modern day & age of ATC, Foreflight, GPS, iPad apps etc, I think it's absolutely ridiculous to require a compass to be calibrated within 3 degrees of accuracy.

    Rob

    * The first pilots to cross the Atlantic

    Leave a comment:

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