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Magnetometer Anomally Garmin G3X

W

Wizane

I'm New Here
Good Afternoon.

I have a GMU 22 which is installed just in front of the vertical stabiliser in my RV-7. Every time I fly I get a yellow/amber warning on the G3X for an AHARS anomaly which can be reset but comes back after a few minutes. Assuming the fault to be based on the close proximity of steel I checked the mounting bolts for the VS and found them to be mild steel. Has anyone replaced these bolts with stainless ones?
 

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I have the GMU 44 mounted in that same location. Never had any issues with that location (it's recommended by Garmin and they sell a mounting kit), but I would be reluctant to replace the bolts holding the tail on. Those are kinda important.

Have you done the magnetometer interference test called out for in the Garmin Installation Manual? It has a rather lengthy suggested list of things to turn on & off and to move to see if any one thing affects the magnetometer.
 
Hi,

Yes, I have done the interference check and all is within limits. The rudder was the largest reading which was still well within the range. I am pretty sure the builder bought everything either from VANS or from the OEM such as Garmin so I doubt there is anything unusual installed.

I am doing my Permit inspection over the next few days so I can do another test with the panels removed and see if there is any change.
 
Connector

I would check the quality of the terminations (pins) in the CPC and at the GSU 25x.

The GMU 22 isn't going to throw a "fault" because of a few non-moving ferrous bolts nearby.
 
Don't replace the bolts! Something else is going on. I had my GMU 22 in that same area on the deck below the VS/HS and it worked great there.

Since the bolts don't move around in reference to the GMU 22, they should be no issue. More of an issue would be the large weldment on the elevators and rudder that do move around back there.
 
It's possible for ferrous components such as bolts, weldments, and cables to become magnetized, which will affect a nearby magnetometer. There are ways of degaussing items if this happens.

However, before touching any hardware, I would verify that the magnetometer calibration was properly done at a magnetically clean site, i.e. a designated compass rose. I have seen this type of issue with otherwise-good magnetometer installations that were calibrated next to a hangar, in an area with a lot of buried rebar, etc.
 
Them are fighting words

I am fighting the same issue.

Garmin support said to look for loose hardware in the tail.

Also, steel screws that are dropped can become magnetized with earth's magnetic field.

I have been trying to re do the GMU11 calibration, but whenever I start the calibration with the engine running, I get a "aircraft in motion" fault, so never can get it re-cal'd. I am thinking of doing the cal with the engine off and just dragging it around by the nose wheel....

Today I am going to take a simple compass and walk it by the tail and see if it can detect any changes or magnetic anomalies.

Let me know how you resolve this.

This reminds me, I still need to do the GDU25 rigidity testing.
 
John, for what it's worth, I did my calibration on a "clean" blacktop surface (hopefully no rebar since it's not concrete), far away from any buildings, lights, towers, steam locomotives, etc. We don't have a compass rose at our airport, so I laid out a N-S line with tape using an accurate compass. Pushed the plane around with the tow bar with one of us in the plane (engine off) following the G3X call-outs and the other person pushing it around as needed. Have had to do this THREE times, as it has to be repeated when the ADAHRS is replaced. Yes, my ADAHRS has been replaced twice. That's a story for another day.

But getting back to the original post...yes, check all those connections that are mentioned, do the magnetometer tests and calibrations again if needed. Pay special attention to the ground wire(s), as they can often cause intermittent problems. If that doesn't yield any results, I'd contact the G3Xperts and get their input. They've pretty much been there, done that.
 
PilotjohnS said:
It would be really nice if we could do this cal in the air.
Click to expand...

Nice...But not feasible.

Doing this in flight would mean adding another set of variables (namely the strength of the field would now be dynamic) to the already complicated algorithm in order to build the "map".

Imagine a juggler with 4 plates on the end of sticks -- now change the length of the sticks while keeping the plates in the air, and spinning...

I can see that overwhelming the existing sensor and processor capabilities.

edit: scratch the "not feasible" comment -- since apparently Dynon can/does do it. Not sure it's the same sensor, algorithm, accuracy, etc. but I'll defer to Paul's experience.
 
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bjdecker said:
Nice...But not feasible.

Doing this in flight would mean adding another set of variables (namely the strength of the field would now be dynamic) to the already complicated algorithm in order to build the "map".

Imagine a juggler with 4 plates on the end of sticks -- now change the length of the sticks while keeping the plates in the air, and spinning...

I can see that overwhelming the existing sensor and processor capabilities.
Click to expand...

And….the Dynon Skyview does in-air calibration quite well…..
 
Magnetometer anomaly

Wizane said:
Good Afternoon.

I have a GMU 22 which is installed just in front of the vertical stabiliser in my RV-7. Every time I fly I get a yellow/amber warning on the G3X for an AHARS anomaly which can be reset but comes back after a few minutes. Assuming the fault to be based on the close proximity of steel I checked the mounting bolts for the VS and found them to be mild steel. Has anyone replaced these bolts with stainless ones?
Click to expand...

If you run out of troubleshooting ideas before the problem is solved, you may try removing the actual AHRS portion of the system. Just pull them out and rotate them around gently, as if you're listening for loose screws/nuts/washers inside the AHRS box. Repeat with the magnetometers. I once assisted with troubleshooting "magnetometer anomalies" only to eventually find loose ferrous parts within the AHRS box. I am not kidding.
I opened the unit, reinstalled the hardware with appropriate loctite, and the problem was solved immediately. The mag data flows through AHRS.
 
I mounted mine to the MFD. Garmin dissuades customers from doing this, even though the mounting holes are already present to do so. I believe it’s because of possible flex in the panel and instability in the ADHRS. My panel is carbon fiber and aluminum and pretty firm. My first flight should be this month, bit no issues taxiing and otherwise. Many others have also installed this way and report good success.
 

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Wizane said:
Good Afternoon.

I have a GMU 22 which is installed just in front of the vertical stabiliser in my RV-7. Every time I fly I get a yellow/amber warning on the G3X for an AHARS anomaly which can be reset but comes back after a few minutes. Assuming the fault to be based on the close proximity of steel I checked the mounting bolts for the VS and found them to be mild steel. Has anyone replaced these bolts with stainless ones?
Click to expand...

You can get an app for your phone that measures magnetic strength. Get that and move the phone all around that area looking for strong signals. In the past, a few guys have had issues with the SS cable for the seat belts becoming strongly magnetized before getting them. Degaussing fixed it for them IIRC. WHile bolts shouldn't be an issue back there, if you happened to have put all of them in one of those magnetic dishes for holding parts, that could be enough to make the unit go bonkers. Same goes for magnetic screw drivers, if they are strong enough.
 
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the're steel

I was surprised to find that the metal shell of the connector on my GMU-11 itself is magnetic - plated steel. Go figure.

Also the connector shells (not the back shells) of the pricey but nice Garnin connector kits.

So it looks like the distortion caused by a non-magnetized steel object nearby can be tolerated by compensation if its position is fixed and stable, but maybe not some control cables flopping around or vibrating mounts.

Ron
 
Final fix

PilotjohnS said:
I am fighting the same issue.

Garmin support said to look for loose hardware in the tail.

Also, steel screws that are dropped can become magnetized with earth's magnetic field.

I have been trying to re do the GMU11 calibration, but whenever I start the calibration with the engine running, I get a "aircraft in motion" fault, so never can get it re-cal'd. I am thinking of doing the cal with the engine off and just dragging it around by the nose wheel....

Today I am going to take a simple compass and walk it by the tail and see if it can detect any changes or magnetic anomalies.

Let me know how you resolve this.

This reminds me, I still need to do the GDU25 rigidity testing.
Click to expand...

My final fix was to calibrate the magnetometer. I tried several times with the engine running and each time i would get a fault that said plane is in motion, and it would never calibrate.
So one day, instead to go to the gym, I pulled the plane far away from the hangars onto an asphalt pad,left the engine off but fired up the g3x in configuration mode, and pushed the plane around in a circle to calibrate magnetometer. Since then, I have never seen a mag fault
 
PilotjohnS said:
My final fix was to calibrate the magnetometer. I tried several times with the engine running and each time i would get a fault that said plane is in motion, and it would never calibrate.
So one day, instead to go to the gym, I pulled the plane far away from the hangars onto an asphalt pad
Click to expand...

You were previously trying to calibrate the magnetometer next to a hangar?
 
I have a GMA22 in the wing tip. About one or two minutes after turning on my LED recognition lights the magnetic anomality alarm comes on.
After ten minutes of flight or so it´s gone.
I believe the starting current triggers the alarm and when current stabilizes
the alarm goes off. I plan to put a shield around the cables in the wing tip.

Good luck
 
RV-14A AHRS magnetic deviation

I was getting AHRS Magnetic Deviation warnings all the time. Always seemed to have an accurate heading and the autopilot was not affected by them. I moved the temperature probe out of the bay next to the magnetometer and that helped somewhat. After a fresh calibration I only saw the warnings when flying east.

A gauss app on my iPhone showed a strong signal from my landing gear and brake disk. I tried degaussing the landing gear and brake disk with no luck. I finally bit the bullet and made an extension cable and moved the magnetometer out to the wing tip. Have not had any problems since.
 
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