So I'm trying to test my Garmin autopilot system and the boot-up AFCS preflight test fails every time. I am beginning to think it is a problem with the GMC 507 autopilot mode controller. To start, let me say the system consists of a non-certified G5, the GMC 507 mode controller, 2 GSA 28 servos and a GMU 11 magnetometer. Here is what I have done/found:

  1. The wiring has been checked about a dozen times with an ohm meter and the pins are correct and there are no shorts, opens or otherwise.
  2. The configuration menu shows CAN bus communication with all units with 0% error rate.
  3. The servos have LEDs that are blinking green indicating that normal communication is occurring.
  4. The GMU 11 which is at the end of the CAN bus shows up fine on the G5, which is the other end of the bus. Both of these have the CAN termination block installed and no other device has a CAN termination.
  5. On boot, it enters the preflight AFCS test and after a few seconds shows a message that AFCS preflight failed.
  6. After #5 and going into config it shows the GMC 507, and the 2 GSA 28s with red Xs indicating a problem.
  7. On the configuration screen for the GMC 507, it shows the "Attitude Calibration" as "Invalid"
  8. After #7 I again performed the attitude calibration for both the G5 and the GMC 507 with the same results. Note it says they have to match for the AFCS to work. The results from this I think should match but with the fuselage level, the G5 shows a pitch offset of +7.9 deg (Instrument panel angled back 8 deg measured with a digital protractor), but the offset for the GMC 507 shows -10.5 deg for the pitch offset. I would think they should be the same.
  9. I then tried it with the panel as near vertical as I could get it rather than having the fuselage level. This time the G5 offset was +0.9 (A change of -7 deg), but the GMC 507 was -2.7 (a change of +7.8 deg). I measured the panel tilt with the digital level and the G5 is within 0.1 deg in both cases and the change in tilt from one test to the other was exactly 7 deg, not 7.8 like the GMC 50 calibration showed.


Does anyone with a Garmin system know if their mode controller offset matches their EFIS offset. I have the G5, but I would think a G3 would be the same. I have been working with Tech support but its slow because I have to wait several hours for a response usually, or like right ow until tomorrow. Trying to work this out as I don't have much else before covering the fuselage. Would like to ground test it successfully while access is good.

Thanks,