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D-180 Compass Heading vs GPS Heading

bobg56

Well Known Member
Has anyone noticed that the magnetic heading between the Garmin 495/496 and D-180 EFIS gets off by sometimes 10-15 degrees. I've done a compass calibration and even re inputted the Inclination angle, I've adjusted the heading to more align with the GPS using the menu keys on the D-180...I've compared the GPS heading to my Fore Flight App and they are spot on. Once I adjust the D-180 to the GPS heading its good, as long as you don't turn more than 20 degrees then it starts to deviate. It has always been a little off but never by this amount, I'll have to check and make sure the rear baggage panel has no magnetic screws, I've been in there for the Condition inspection and may have gotten the screws mixed up, I believe they were stainless steel...just wondering if this is something others have notice, or is this something that the D-180 does and I'll have to live with...
 
I corrected this type issue in 2 planes that had their remote sensors mounted a few degrees off. New mounts at the proper angles fixed both.
 
I don't have any of the mentioned equipment, but... Doesn't the gps measure your ground track, not your heading? (e.g., how does it know about any wind correction angle?). Although 10 degrees sounds like a lot!
 
I don't have any of the mentioned equipment, but... Doesn't the gps measure your ground track, not your heading? (e.g., how does it know about any wind correction angle?). Although 10 degrees sounds like a lot!

This! GPS doesn’t know heading, it knows track, and wind correction angles of ten degrees aren’t that outlandish - especially if you consider that the magnetic compass can easily be off by five degrees, and its tough to read them to closer than a couple of degrees anyway....
 
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Compass swing?

I have similar/equivalent equipment including Garmin Gpsmap 296 and Dynon D180 with remote magnetometer, as well as a separate whiskey compass.
Generally the compass headings and the GPS track align, unless there is a significant cross wind.

Bob, when you say you have calibrated the D180 compass, do you mean that you have done an actual compass swing sitting on the compass rose at an airfield, in flying attitude, per the procedure in the D180 installation manual? If there is a problem with the D180 then it should show up here. Also, has there been any change to electrical wiring or eqipment in the vicinity of the magnetometer that may be affecting it?
 
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I've got both a Dynon 180, and a Garmin 496. When I first got the airplane back in 2013, I had it on a on the ground compass rose---twice. After that, I just gave up.:rolleyes::rolleyes: Usually its within 2 to 5 degrees of my 496's track number, but sometimes its like your readings. One time, I was getting radar vectors from Savannah APP control. (Class C airport). I just flew the track heading the 496 said, and they were happy. To be honest with you, I hardly ever look at the compass---I just follow the pink line. ( I just noticed you're in PT City. Ask Vic or Vern about it)
 
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The Gps on the ground shows the magnetic heading, its set up to auto correct for magnetic deviation, however you need to be moving on the ground for it to read correctly. I'll check the remote compass mounting, the D180 install manual says to make sure the angle of the D180 and remote compass are the same and for any ferrous screws, no wiring has been added. I can use the GPS heading I guess for ATC vectors. I did at one point use the compass rose at KFFC...it just seems a bit worse now than it was. Thanks for all the suggestions.
 
Recent example in my 12 --

Was a fair amount of wind on ground, but a bunch at Alt. Indicated 50 knots direct cross wind. My track and heading were 30 degrees different. A 12 is a light plane and the tail is fair size, it can deviate a bunch in a serious crosswind. I will also mention that I took a pic of the airport I was heading to. AP engaged. The prop was not in the pic of the airport. Was going sideways a bunch.
 
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