Garmin GI 275 HSI/GMU-11 Inaccuracy

[Tom 4536]

1 hour ago, andrewf15 said:

Has this problem been solved? I have the installation manual describing how to fix this issue.

No, it has not been resolved. The magnetic interference and vibration tests have been repeated and checked out OK. I would love to see what the installation manual says. I have all but given up that the magnetometer reading will be closer than 9 degrees.

Thanks.

Tom

[Aerodon]

On 12/3/2020 at 9:54 AM, Tom 4536 said:

The magnetometer is installed about 3 feet in from the end of the left wing. The installer said he did the magnetic interference test and and the calibration and when he contacted Garmin about the inaccuracy, Garmin said there is nothing in the GI275 software to make any corrections.

I call BS.  Find another installer to do both the magnetic interference test and the calibration.  By definition, the calibration is the 'software' to make the corrections.

(and if you can find an install manual, it's easy to do both these procedures yourself).

 

Aerodon

 

 

[Tom 4536]

3 minutes ago, Aerodon said:

I call BS.  Find another installer to do both the magnetic interference test and the calibration.  By definition, the calibration is the 'software' to make the corrections.

(and if you can find an install manual, it's easy to do both these procedures yourself).

 

Aerodon

 

 

I've contacted 4 installers and none of them will take on this problem. My only solution is to try to get a copy of the calibration procedure and try to fix the problem myself. Getting the calibration instructions is next to impossible. 

[Aerodon]

If your installer was lazy and did the calibration near hangars or airplanes, I would not be surprised if this translated into a 10 degree error 'out in the open'.

 

Aerodon

[Tom 4536]

36 minutes ago, Aerodon said:

If your installer was lazy and did the calibration near hangars or airplanes, I would not be surprised if this translated into a 10 degree error 'out in the open'.

 

Aerodon

My calibration was done twice (about 2 -3 months apart) on a large asphalt pad about 1/4 mile from any structures. There are seldom any other planes or anything else on the pad. I don't think anyone would classify my installer as "lazy". He seems very conscientious and truly concerned about the error. He just hasn't found a solution to the error and Garmin has been no help.

Tom

[andrewf15]

In the maintenance manual, after the directions to perform the GMU11 calibration, the next section is for magnetic deviation.  You must perform a compass swing and find the average deviation of the unit.  Once found, you must physically turn the GMU11 the amount of deviation and keep trying until all the deviations are under +3-3.  The Mooney we installed dual 275's had the same problem until we tried this. Hope this helps