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GFC 500 - AFCS preflight test failed

After installing a brand new GFC 500 autopilot with a GMC 507 controller and 3 servos on my Socata TB20, we are receiving the following message immediately after AP power on:

AFCS preflight test failed

And nothing works after that. Does anyone have any idea what may be the issue? All the components are brand new and all the connections seem to be ok.

Under G5’s system diagnostics all the 3 servos and the GMC 507 are marked with a red cross and with the above error message. There are no can bus errors or other obvious issues.

The installer has no clue about what could cause this.

LRIA, Romania

What did Garmin say (assuming your installer is in touch with them)?

always learning
LO__, Austria

They haven’t said anything, so far. I’ve heard rumors there are some issues with the GSA 28 servos, but they are all new, I wouldn’t expect any issues so soon.

I still hope it’s something that can be solved via a software configuration, maybe…

LRIA, Romania

Red cross against a LRU usually means the G5 (or G3X etc.) can’t communicate with it.

Are you sure the Canbus is correctly wired and terminated?

Last Edited by Jacko at 24 Jul 09:20
Glenswinton, SW Scotland, United Kingdom

We have two airplanes with Garmin a/p systems at Glenswinton. Fabulous piece of kit. Absolutely no problem with any of the LRUs.

Glenswinton, SW Scotland, United Kingdom

Well, the issue was the AP disconnect wires were not connected to the yoke button!

As strange as it sounds, if the GMC 507 part of the AP disconnect wire is not connected to the servos AP disconnect wire, the AP cannot initialize properly.

The GFC 500 system should generate a readable and user friedly error message, instead it just shows a red cross for any issue, just like1970s consumer electronics.

Everything seems to work fine. I cannot find the specific servos torque settings for Socata TB20 (maybe @Peter knows them) but it seems pretty snappy and powerful enough. Tomorrow I will perform some flight tests, hopefully without any new error messages. Fingers (red) crossed. Pun intended :)

LRIA, Romania

There may be a guide to autopilot tuning flight test procedure in your installation manual.

If not, you could follow Appendix A of Garmin doc 190-01115-01. That’s for the G3X system, but the procedure should work for yours.

Glenswinton, SW Scotland, United Kingdom

Great to hear it’s fixed. You have an awesome kit in a great plane now.

As strange as it sounds, if the GMC 507 part of the AP disconnect wire is not connected to the servos AP disconnect wire, the AP cannot initialize properly.

Rightfully so and sounds like a well designed autopilot test cycle. Imagine pushing the AP disconnect button when breaking out at minimum and nothing happens. That would be a startling moment.

always learning
LO__, Austria

This shows that someone in Romania gets even less help from “the industry” than someone “more central”.

Administrator
Shoreham EGKA, United Kingdom
9 Posts
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