Gfc500 disconnect

[PT20J]

2 hours ago, Tom 4536 said:

An update on my GFC 500 disconnect problem. My avionics shop replaced each GFC 500 component, one at a time, and checked all the wire connections and it did not solve the problem. Garmin recommended a “Factory Reset” of the GFC 500 and my three previously installed GI275s. It solved the problem but meant everything had to be re-calibrated. My avionics shop had promised to work on the problem until the autopilot worked and they kept their promise.

Wow. Wonder why Garmin didn’t suggest that first, AND I wonder if that was just a Hail Mary, we're out of ideas, try this suggestion, or if they know something.

This would tend to point to a misconfiguration of some sort. Configuration parameters would normally be stored in a table in memory for software lookup during operation. It’s possible for a table to get corrupted even if everything was originally entered correctly. It would depend on how robust and fault tolerant the software is.

Skip

[carusoam]

Great follow-up Tom!

Thanks for sharing the details.

Best regards,

-a-

[ZuluZulu]

On 6/15/2021 at 11:18 AM, PT20J said:

It may not be the same problem. In complex systems, there are often multiple issues that can precipitate the same result. The standard response for any autopilot when it gets confused is to disconnect. This is a safety measure to prevent the autopilot for driving the aircraft outside the safe envelope. 

By the way, this is why it is a good idea to keep your hand lightly on the yoke when the autopilot is flying in any critical situation such as low altitude or during an approach. If it does something wonky or disconnects you are "in the loop" to take control immediately and prevent an excursion.

Skip

I have the YD and was having issues with NAV mode disconnecting, sometimes frequently, and always unpredictably.  The only way to tell was to closely monitor the G5 or the GMC 507 for the GPS/indicator light to go out.  With Garmin's help, the shop traced it to a bad data port on the GTN 750.  No similar disconnections since.

My new issue is that the HDG indication on the G5 sometimes turns yellow, unsure of the cause but it seems to happen most often close to the ground, which kicks off the AP if in HDG mode.

[ArtVandelay]

I have this problem as well, 3 times in the last 4 months, avionics shop already recalibrated G5/G3X and I just completed a vibration test, results to be sent back to Garmin.  Curious if anyone who had this problem and found the problem.

[PT20J]

I had one time where it disconnected when I commanded a climb from cruise flight and it disconnected again twice when I reactivated the AP. It's never done it again. I sent the logs to Garmin and it was a miscompare between the G3X (GSU 25D) ADAHRS and the AHRS in the GMC 507 which is used for error checking.

In addition to the logs that get saved on the SD card, the G3X also stores an internal error log that you can find in Config mode.

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