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G3X/GMC507/GMU11 issues - G3Xpert please help.

jamesrw2002

Active Member
Hello All,

I experienced something today that was a bit concerning, as I've never seen it before.

Took a 45 minute flight for breakfast with no issues. Beautiful day to fly!

After Breakfast, after start up I noticed the TAS and AP annunciators on the G5 and PFD X'd out. I chalked this up to a start up glitch and decided since I was on the ground, I'd go ahead shut down, power off, then power back up and hope it all came back.

What happened after I shut down and turned power on reminded me of a CAN Bus failure. things sort of flickering in order. So instead of starting up, I shut the avionics down again and booted up in Configuration mode.

Indeed, there was some cycling of components but then everything come on solid with max Network error rate of 10% - with the exception of the GMU-11 which showed failed (even on the page it said "Magnetometer Failed.") Oddly some of the other components weren't quite booted up appropriately either... Pitch Servo was one of these things as I recall.

Suspecting maybe a CAN BUS failure at the GMU-11 I tried reseating the plug to it - also checked the security of the wires and all seemed good.

Started back up - No Heading info. (The G5 had it, but was not sharing.) I decided to limp it home and troubleshoot it there. What I did not have at take off:

- HDG info in my HSI on the G3X
- TAS
- Wind information
- AP

Somewhere in the flight I realized that the G5 wasn't sharing my BARO setting with the G3X... strange.. and then, about 30 minutes in to the flight I did a few steep turns* and in them, the ADAHRS Failed. I first noticed a substantial difference in pitch between the G5 and it and what I was seeing outside. I don't recall there being any annunciators at first but THEN** it kicked in to reversion mode and started taking data from the G5 with a Reversion annunciator (heading and ATT info was being displayed on the PFD from the G5, I presume.) A few seconds later (less than a minute by my guess) the G3X ADAHRS came back online and everything started working fine. (I had HDG information in the HSI where I hadn't until the G5 stepped in during the ADAHRS fail.)

I landed, shut everything down and powered everything up a few times. No issues.

I've had these Avionics in the aircraft since March of last year with no real issues to speak of. I am running the following versions of everything:

G3X: 8.81
GSU25: 2.60
GMU11: 2.10
GMC507: 2.90

I believe all of these came packaged in software update 12.0.

To make matters worse, I did not have my SD cards in during this flight (I stupidly left them at home because I was updating databases...)

What in the world is happening!??

*I have to wonder if the steep turns didn't kick things in to alignment. In the work jet, we have an inflight alignment procedure that IIRC asks you to preform several banked turns to stand everything up.

** Why wasn't the G5 sharing HDG info all along?
 
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Anything other than '0' on the network error is a problem, AP is usually one of the first things to drop off with a CAN bus error.
 
With only two wires and a shield, if a CAN bus is installed correctly initially there are only a few things that can go wrong. If a CAN wiring issue is suspected, there is a detailed step-by-step troubleshooting guide in the installation manual: section 2.3.1.36 in the current revision (AN).
 
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