Last weekend I couldn't get the autopilot to stay engaged on the ground, and I was getting the logged error message of "Attitude Comparator". I knew something wasn't setup, because in the Garmin G5's Device Information, the GMC507 showed up on the CAN bus, but it did not have the green check mark next to it. When I looked at the AP Controller information, it indicated the Attitude Calibration was not complete? I was certain I leveled out the fuselage and leveled the unit, but maybe I needed to do it again?
So I calibrated the pitch/roll again, but that didn't seem to fix it.
Googling this GMC507 calibration error led me to the GFC 500 maintenance manual (http://www.rvplane.com/pdf/Garmin/190-02291-01_06.pdf). Looks like its a separate attitude calibration in the Mode Control Panel.
Sure enough, there it is. I clicked "Calibrate Pitch/Roll.." and then....
BOOM! The GMC was showing with a healthy status indicated by the green checkmark. I was able to engage the autopilot now and make sure it moved in the expected directions, the disengage button worked, and I could override the servos if needed.
The neoprene intake adapter for my filtered airbox (FAB) had started to fail on the top (closest to the engine). I attempted to stitch it together with some thin 040 safety wire, but that didn't work well at all. Time to rebuild.
The neoprene adhesive is quite amazing. Once you set it up and let it get tacky, it instantly bonds.
With that setup, I put the cowl back on the engine and went for a test flight. The autopilot is a little different than my GRT, so there were some things to get used to. For example, you just can't hit the ALT button and select an altitude - you also have to set a VS or IAS to climb/descend to that altitude with. I will say it is very very nice to have a stand-alone controller for the autopilot. The GRT worked fine, but it was a lot of clicks and knob rotations to get things setup.
Great to be in the air again! It's been nearly two months since I have been up.
The approach functionality worked perfectly on the first try. I flew the RNAV 16 for KDMW and the needles stayed perfectly centered.
It also flew the procedure turn perfectly before I got on the glideslope. I have much more playing to do with this autopilot, but so far I am very happy with its performance and simplicity of use. I still have some tuning to do of settings and familiarizing myself more with the features and functions. I also have another G5 to install to be dedicated as the CDI.
My only disappointment with the autopilot is I was hoping it would understand the ARINC output from my Grand Rapid ARINC like the TruTrak autopilot did. Unfortunately it didn't appear as a valid NAV source, and I think I know why. Digging through the GRT manuals, it looks like the only commands the GRT sends is a roll and pitch angle/command. I think the Garmin G5 is expecting much more than these two commands, as when it is tied to my Garmin gtn650, I get distance to next waypoint and track to next waypoint in the arinc signal displayed on the PFD, which clearly isn't in the GRT stream. Not the end of the world, I just need to duplicate a little bit of work.
It's great to be near the end of this installation! I was totally unprepared for the amount of work that it took to install the GMC500 autopilot - my tally of time comes up to 48 hours! I can see now how the avionics shops charge as much for the labor as they do for the equipment!
Last Modified: August 13, 2023