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GFC 500 Service Alert - Not sure if this affects any Mooney owners


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I saw this on Beechtalk (https://www.beechtalk.com/forums/viewtopic.php?f=21&t=213785) - not sure if this affects anyone here:

https://atlaske-content.garmin.com/filestorage//email/outbound/attachments/22109A_Time1669064630332.pdf

 

EDIT: It affects all GFC500 installations where a GSA28 pitch trim servo is installed.

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Would have been nice of Garmin to describe the condition. Understanding the failure mode shades some light on inner workings which could come in handy in other emergencies that "shouldn't happen".

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12 minutes ago, PT20J said:

Must not happen very often. I read a lot of complaints about pitch oscillations and failing servos, but haven’t read about trim runaways. 

The former are less likely to cause High Anxiety than the latter.  ;)

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I just checked the logbook from our GFC500 install, and we have the GSA-28 pitch servo described in the Service Alert / Service Bulletin.  So, it seems to affect at least one Mooney owner.

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I’ve posted under a different thread regarding GFC500 pitch oscillation. I have not updated that thread, but I will in detail.
 

In short, it is not been fixed in spite of 4 Garmin guys flying down to inspect the installation with nothing of relevance found. In my case, I’d give Garmin an “A” for their responsiveness and support. Trek has been awesome!

Maybe this software update will address other issues.  Like another poster noted , this cannot be a frequent problem or wouldn’t it be an AD?

Happy Thanksgiving my fellow MooneySpacers! Be safe! 

 

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I believe the Electric Trim would be inop if you follow the SB. I talked to our Garmin Dealer yesterday. He had not even heard of the SB yet, sounds like Garmin didn’t give them any heads up this was coming. Not required for pt91 obviously.

Perfect timing, in the middle of replacing the KFC150. Should have the airplane back soon, probably without a fix for this issue…

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1 hour ago, Scottknoll said:

I believe the Electric Trim would be inop if you follow the SB. I talked to our Garmin Dealer yesterday. He had not even heard of the SB yet, sounds like Garmin didn’t give them any heads up this was coming. Not required for pt91 obviously.

Perfect timing, in the middle of replacing the KFC150. Should have the airplane back soon, probably without a fix for this issue… emoji58.png

Not sure if it still works this way or not, but my dealer told me a year ago that Garmin sends out an email blast to its dealers on Fridays with a summary of new service issues.

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Just got a call from my installer who installed my gfc 500 this year. Just going to pull the breaker and do some extra hand flying practice rather than just disable the trim.

Hopefully they fix the software soon.

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Good evening everyone,

   I'm hoping I can address all the questions on this thread in regards to the recent service alert for the GFC 500 we had to issue.

 

the problem very rarely happens, but we've had a couple of reports of it from the field and did verify there is an issue with the system where the pitch trim can go into a runaway condition when the autopilot is first engaged. this can be quite uncomfortable with the plane trimmed out and on a flight plan and then engaging the A/P and it could do this. We've been working closely with the FAA on it and as it has been mentioned is able to be corrected with a softrware update for the G3X, GI 275 and G5 systems. we're diligently working on this as you can imagine to get this all completed, submitted to the FAA for approval and then to the field. the plan is to have this completed by the end of the year.

   in the meantime the recommendation is to pull the breaker on the GFC 500 or have the Garmin dealer disable the pitch trim function in the configuration of the GMC 507.

 

as for how the dealers are alerted to problems and bulletins like this, no we do not bundle all of the bulletins and send them on one given day. when these are posted to the dealer resource center website for our service centers, it is also sent to the email address we have on file in our system. unfortunately if this email address has not been verified it may not get to the right person(s) at the dealership. but we do our best to re-iterate this when the dealers call into us as well to get the word out to the field.

 

   I know I've been working on a couple of things for some Mooneyspace pilots and as you can imagine when this hit a head we had to put our undivided attention on it, but I can assure you I've not forgotten and will get with you as soon as I can on the issues we're working on.

 

   Please let me know if there are any questions on this issue and I'll do what I can to get any details out to the group.

Edited by TrekLawler
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The last conversation I had with Ron Blum before his untimely passing was regarding trim runaways (this was earlier this month and well before, and unrelated to, the current GFC 500 issue). Ron pointed out that the design requirement is usually some maximum stick force after 3 seconds of continuous trim operation which places a design limit on the trim servo speed. The 3 seconds is supposed to allow for the time it takes an average pilot to recognize the problem and disable the electric trim.

I did a test in my M20J with nose down trim (because it was easier to use a spring scale to measure the stick force in that direction). Trimmed for cruise, 3 seconds of down trim with a GFC 500 runs the trim to the down limit and requires a constant 40 lb pull to maintain level flight. If you don't catch it and let the airspeed build it takes much more than 40 lbs to regain control. I didn't attempt to measure the stick force with 3 seconds of up trim but it seemed about the same. However, it is possible to run the trim for longer than 3 seconds before hitting the up limit and the airplane will stall at that trim setting unless very high stick forces are applied. If the airplane stalls with full up trim, it will most probably enter a spin.

My point is that a trim runaway can create very high stick forces very rapidly. Best to follow Trek's recommendations until they get this sorted out.

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More than once in my career I have seen an attempt to fix a hardware problem with software, and it usually introduced other problems because the fix treated the symptom rather than the cause. But it was cheap to implement.

However, the GFC 500 Is almost all software, so I would expect a software solution to be the appropriate remedy.

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