Airpath compass correction instructions.

[Robert Lees]

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.

[PA1195]

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

[astjp2]

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...

[PA1195]

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

[Ragwing nut]

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.

[PA1195]

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

Gary

[3Dreaming]

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-magnetic-model-out-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.

[PA1195]

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-magnetic-model-out-cycle-release

Gary

[Hank Jarrett]

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

[PA1195]

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

Gary

[astjp2]

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

[PA1195]

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

[3Dreaming]

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°.

[Robert Lees]

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

[PA1195]

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