G3X Heading "bug"

[PT20J]

There is a software bug in the G3X (v9.15 and earlier). According to the AFMS, if the GMU 11 fails the G3X is supposed to display a red X over amber HDG and display magenta GPS TRK on the HSI. But, instead, it continues to display white HDG as normal. What is happening is that the logic is not switching to TRK upon GMU failure and the ADSU 25D is continuing to compute HDG but without GMU input so the heading will drift over time. The G5 does properly switch to TRK. I don't have a GI 275, so I don't know how it behaves. I reported it to Garmin and after some back and forth, Support was able to reproduce it and passed it on to Engineering for resolution.

[EricJ]

16 minutes ago, PT20J said:

There is a software bug in the G3X (v9.15 and earlier). According to the AFMS, if the GMU 11 fails the G3X is supposed to display a red X over amber HDG and display magenta GPS TRK on the HSI. But, instead, it continues to display white HDG as normal. What is happening is that the logic is not switching to TRK upon GMU failure and the ADSU 25D is continuing to compute HDG but without GMU input so the heading will drift over time. The G5 does properly switch to TRK. I don't have a GI 275, so I don't know how it behaves. I reported it to Garmin and after some back and forth, Support was able to reproduce it and passed it on to Engineering for resolution.

Did you deliberately fail your GMU to find that or did you find that as part of a failure event?

[PT20J]

4 hours ago, EricJ said:

Did you deliberately fail your GMU to find that or did you find that as part of a failure event?

I failed it as part of my ongoing FMEA. I had my avionics installer agree that it was a minor deviation to put the GMU on a separate CB rather than combining it with the GSU 25D because I saw no need to deprive the G5 of the magnetometer in the event the GSU 25D or it’s circuit popped the breaker. Garmin told me there was no technical issue; they were just trying to cut down on the number of breakers by combining circuits to make the installation easier. I actually noticed this a couple of years ago but it took a few contacts with different people over time to finally get to someone who agreed it was a real issue. 

[blaine beaven]

On 3/25/2024 at 12:37 PM, PT20J said:

I failed it as part of my ongoing FMEA. I had my avionics installer agree that it was a minor deviation to put the GMU on a separate CB rather than combining it with the GSU 25D because I saw no need to deprive the G5 of the magnetometer in the event the GSU 25D or it’s circuit popped the breaker. Garmin told me there was no technical issue; they were just trying to cut down on the number of breakers by combining circuits to make the installation easier. I actually noticed this a couple of years ago but it took a few contacts with different people over time to finally get to someone who agreed it was a real issue. 

@PT20J I hope that you’re writing a book with all your experiences… you could pitch it to everyone that buys a G3X!

[Fly Boomer]

On 3/25/2024 at 11:49 AM, PT20J said:

There is a software bug in the G3X (v9.15 and earlier). According to the AFMS, if the GMU 11 fails the G3X is supposed to display a red X over amber HDG and display magenta GPS TRK on the HSI. But, instead, it continues to display white HDG as normal. What is happening is that the logic is not switching to TRK upon GMU failure and the ADSU 25D is continuing to compute HDG but without GMU input so the heading will drift over time. The G5 does properly switch to TRK. I don't have a GI 275, so I don't know how it behaves. I reported it to Garmin and after some back and forth, Support was able to reproduce it and passed it on to Engineering for resolution.

If those guys don't pay you for your input, they should.