Magnetic field

[PapuaPilot]

just a note: if you use a glass panel and have the magnetometer in the wing you do not need a panel mounted compass.

you only need a magnetic indicating device.

David Kelm
A&P.IA,DART,DARF
7SS 912is Garmin Touch

I was about ready to say that too.

[efwd]

I have a glass panel with magnetometer. What is a magnetic indicating device?
Im guessing that its the screen that presents the Magnetometer input?

[nyrikki]

I have a glass panel with magnetometer. What is a magnetic indicating device?
Im guessing that its the screen that presents the Magnetometer input?

Yes on the Garmins it will be on the top. If you haven't calibrated it or the error is bad enough it will be yellow but should be white if it thinks things are OK. If it is using GPS it will typically be Magenta with "TRK". I have no idea on other manufactures.

Be sure to ask the FBO the last time their compass calibration pad was actually calibrated if you depend on the magnetic track when you calibrate it.

Some places have a significant declination change and it may be hard to know the last time the lines were painted at some airports. I think the surveys are valid for 5 years and if you are shooting for more than FAR compliance you could be way more then 10 degrees off if it is at the tail end of that if you live in a area with lots of drift.

Probably not as big of an issue these days with GPS but if you are a big user of dead reckoning and manual pilotage it will cause problems as well as be out of compliance with the FARs.

Edited to add:

If you are in the West of the US I think this changes more but it is about a degree per year for me, so near the end of a 5 year survey a compass calibration pad will be off by close to 5 degrees.

The 10 degree limit is for large aircraft, but a really good idea IMHO for smaller craft too.

If you live in a place without anomalies you can look up the drift here and try and compensate.

https://www.ngdc.noaa.gov/geomag/declination.shtml

[jtpitkin06]

Josh....Excuse my ignorance but what is degaus and how you do it?

Use a bulk tape eraser. Lots of them on eBay for about $20. The ones made by Realistic Radio Shack are small, powerful and easy to use.

Power the eraser up before you move it into the airframe. Hold the eraser (degauser) against the airframe and work your way all over using a 3 inch circular motion. Do all tubes on all sides. Don’t release the spring power switch until you move away from the airframe a foot or so. It will take several passes to get the residual magnetism down to a reasonable level.

John Pitkin
Greenville Tx

[Danzer1]

I have a glass panel with magnetometer. What is a magnetic indicating device?
Im guessing that its the screen that presents the Magnetometer input?

Eddie, In your case, both the magnatometer and display make up the "device" - one can't be used without the other and yes the combo meets all requirements unless you get an off the wall DAR.

If you are in the West of the US I think this changes more but it is about a degree per year for me, so near the end of a 5 year survey a compass calibration pad will be off by close to 5 degrees.

Greg, the change rate is not nearly that high. In Seattle and most of the West it is 9' (minutes) a year, there are 60 minutes in a degree. So it takes 6.66 years to get to just 1 degree of variation.

YMMV, Greg

[nyrikki]

Eddie, In your case, both the magnatometer and display make up the "device" - one can't be used without the other and yes the combo meets all requirements unless you get an off the wall DAR.



Greg, the change rate is not nearly that high. In Seattle and most of the West it is 9' (minutes) a year, there are 60 minutes in a degree. So it takes 6.66 years to get to just 1 degree of variation.

YMMV, Greg

I shouldn't have linked to that site at the last moment and I did have a mistake with units there so thanks for capturing my mistake. FWIW the Seattle city center and thus airports like BFI are in a fairly stable part of the area but I don't fly out of there.

Some of the smaller GA airports in the Puget Sound area are challenged by quite large magnetic anomalies and that causes massive changes at individual locations that aren't covered by the small change in the site above.

For those in the PNW bremerton just did certify a new rose with only a small no-cal area this spring but had challenges and had to abandon their top choices due to multiple issues.

https://www.portofbremerton.org/medi...rt_2018-04.pdf

And Arlington is unconditional this year.

https://www.arlingtonwa.gov/Document...ertificate-PDF

While I can't find docs for the airport I was talking about, and don't want to spread misinformation about an individual airport. I ran into a problem with helping a friend with his RV-12 last year. We are in an area of complex fault lines and local anomalies so if you are in the PNW be careful of using a compass pad in some of the red areas here if they don't have a recent survey.

https://pubs.usgs.gov/of/1999/of99-514/whole_map.html

Note that map does show the rate change but is a good proxy without calling out a single facility. Two of the major geographical structures around here differ in their trend from ~285° and ~315° and we tend to build near their boundary.

I doubt this is as much of an issue in areas where volcanic and plate activity isn't as active but these localized anomalies can be extreme.

To be clear, I was wrong and assume the local 1 degree annual change we had to account for was related to the website I linked to as I failed to check my units. Just ask the FBO or airport owner if they have these types of large anomalies and verify at another location.