Interesting G3X / GFC 500 audio issue

[PT20J]

Testing on my new panel continues. I am trying to understand what happens when things fail so I won't be surprised by the indications if something untoward happens for real. Ran into an interesting one today.

With autopilot engaged and flying off the G3X Touch, I pulled the AP circuit breaker as one might to disable an aberrant autopilot. The autopilot disengaged as expected. But the autopilot disconnect aural annunciation ran continuously. The red button on the pilot's yoke did nothing. The only way I could silence the noise was to cycle power on the G3X. Think about that for a moment: You are IMC, the autopilot goes nuts and you pull the breaker and the only way to make the noise stop is to disable your primary flight instruments and hope they come back including a AHRS realighment which may be problematic if in turbulence. The only other possibility is to pull the breaker for the audio panel in which case you will only have Com 1.

The problem appears to be that the STC requires connecting the G3X audio to the audio panel and not connecting the GMC 507 to the audio panel. So, the sound is coming from the G3X and not the GMC. The red yoke disconnect button connects to the GMC (which is powered down) and not to the G3X. So a state machine is set in the G3X that apparently cannot be reset without powering the GMC or cycling power on the G3X.

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[N231BN]

Feels good to be a beta tester after spending all of that money right?

[N201MKTurbo]

I put a switch on my unswitched audio inputs. Mostly to stop the annoying traffic and terrain alerts when I’m in the pattern. It would stop your problem too. You just need to remember to turn it back on. But then again, I flew for 35 years without any bitching Betty.

Edited December 11, 2021 by N201MKTurbo

[N201MKTurbo]

I haven't labeled that switch yet. I should so if anybody else flies my plane they know what it is. I was thinking of labeling it "STFU".

[N231BN]

What other alerts does the G3X give? Does it have an option for a silence button?

[Ragsf15e]

Audio like that can be super annoying/disorienting too.  I’d definitely be looking for a workaround like @N201MKTurbo suggested.

[EricJ]

Wouldn't connecting the GMC back to the audio panel be a minor mod? 

[N201MKTurbo]

4 minutes ago, EricJ said:

Wouldn't connecting the GMC back to the audio panel be a minor mod? 

Who would ever know? Do you think your IA would be thorough enough to find it? Do you think the accident investigators would determine the cause of the crash was an improperly wired autopilot audio?

But the issue isn't having the GMC connected to the audio panel, it is having the G3X connected to the audio panel. If you disconnect the G3X, you lose all the alerts. 

Just move two pins on the connector and connect the G3X to the ADF input. Now you have a button. Audio Distraction Function.

[PT20J]

Well, there is a way around this. The emergency procedure in the AFMS states to press and hold the yoke disconnect button first, and while holding it, pull the A/P CB. This should disconnect the autopilot and silence the warning before the GMC loses power and hangs the G3X in alerting mode. It pays to follow the published procedures because there may be reasons for the specific order that are not obvious as appears to be the case here.

I pulled the CB with the autopilot on because I was attempting to simulate failures to see what happens. Because of the distributed nature of the GFC 500 design (the flight director software resides in the PFD, the controls and monitoring are in the GMC, the autopilot software is in the servos and the ADAHRS is in the GSU 25D) it is not clear if any failure other than pulling power will cause such a hang (the A/P CB feeds the GMC and the GSA 28 servos, so pulling it simultaneously kills everything but the FD).

I have always thought it best to pull the CB anytime an autopilot acts up because I don't know if the disconnect switch directly controls anything or just pulls an interrupt on a microprocessor that may already be misbehaving. But in this case, it is clearly best to follow the written procedure.

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[PT20J]

I made a similar post on Beechtalk that attracted the attention of Trek Lawler who responded that the hung disconnect alert on the G3X Touch can be cancelled by touching the AP annunciation in the autopilot status box at the top of the PFD or by pressing the BACK button. I searched the Pilot's Guide and touching the annunciation is listed  as an alternate means of silencing the alert. The BACK button is mentioned as the means to acknowledge an automatic disconnect due to a autopilot or sensor failure. I tried both methods today and they did silence the alert.

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[Ragsf15e]

Those Beech folks must spend a lot more than us or maybe they just smell better.  Either way, Trek hangs out with them a lot more than us!

[PT20J]

2 hours ago, Ragsf15e said:

Those Beech folks must spend a lot more than us or maybe they just smell better.  Either way, Trek hangs out with them a lot more than us!

I noticed that. Perhaps a side effect of proudly proclaiming how cheap we are and complaining about the cost of Garmin repairs.