MORE GFC 500 problems - has anyone else seen this?

[Rick Junkin]

THE PROBLEM:

My GFC 500 disconnects intermittently and the G3X A/P scoreboard displays a flashing red A/P and flashing yellow HDG and PIT. The airspeed turns yellow, and the airspeed trend bar (magenta bar on the right side of the airspeed tape) is pegged at the top but the airspeed is not changing. Here's a pic from a friend's Bo that has the same anomaly. His system will also intermittently flash the yellow HDG and PIT and give the same airspeed/airspeed trend indications even with A/P disengaged. The pic is of that case. You need to zoom in to see the magenta airspeed trend bar.

Has anyone else seen this, or heard of anyone who has?

 

I'm thinking it's an intermittent air data problem. I think the runaway airspeed trend input is tripping the GSU 25 or GFC 500 fault monitors and knocking the A/P offline and showing the airspeed, HDG and PIT as unreliable. My friend's avionics shop contacted Garmin and they said they've seen this in experimental installations but not in a certified installation. They said they've seen it, but offered no diagnosis of what causes it. They said it would be addressed in a future software release, but gave no details as to when or with what level of urgency.

My next troubleshooting step is to pull the GSU 25 circuit breaker and fly with the G5 ADAHRS providing input to the GFC 500 and see if the behavior persists.

It's interesting that the G3X pilot guide talks about yellow/amber indications, but makes no mention of flashing indications or their meaning.

WHY IT'S A BIG DEAL TO ME

I sent this anomaly to Garmin when it first started happening right after my installation last year and was told they already had an open engineering ticket for the issue and they would add my flight data files to that ticket. There have been two software releases since then and the problem persists. I generally avoid using the A/P in "hard" IFR because of my lack of confidence in it. Which of course defeats the whole purpose of having the autopilot in the first place. I've reached the point where I'm ready to devote the time, energy, travel and money to aggressively engage Garmin in the interest of a fix for this issue. I don't want to go through the same ringer we went through with the pitch oscillation issue.

I think if there was a legal accountability approach for resolving this someone else would have already initiated it. I have no idea how many airplanes exhibit this anomaly. But I know for sure of two, and we're at the same home field with brand B and brand M airplanes with nearly identical avionics suites installed by two different, reputable shops.

Anyone have insight on this one?

 

[Ragsf15e]

Yikes, that’s not good.  I agree with your assessment of the problem being in something other than the autopilot.  Maybe ADC, maybe pitot system, maybe g3x?  Have you ever seen the airspeed trend do that when the AP is not engaged?  What does the g5 do when this happens?  Do you have data logging on both (g5 needs a micro sd card).

Im sorry this is happening to you.  Id be pretty mad at garmin too if they just left it hanging for this long…

[TCC]

Since the GFC500 is dependent on a GPS signal in NAV mode, I’m curious if there was any GPS degradation at the time of these errors.

[ArtVandelay]

I would check the log (on sdcard) and look for disconnect and see what errors if any.

[Rick Junkin]

1 hour ago, TCC said:

Since the GFC500 is dependent on a GPS signal in NAV mode, I’m curious if there was any GPS degradation at the time of these errors.

 

2 minutes ago, ArtVandelay said:

I would check the log (on sdcard) and look for disconnect and see what errors if any.

 

1 hour ago, Ragsf15e said:

Yikes, that’s not good.  I agree with your assessment of the problem being in something other than the autopilot.  Maybe ADC, maybe pitot system, maybe g3x?  Have you ever seen the airspeed trend do that when the AP is not engaged?  What does the g5 do when this happens?  Do you have data logging on both (g5 needs a micro sd card).

Im sorry this is happening to you.  Id be pretty mad at garmin too if they just left it hanging for this long…

Sorry, I should have mentioned I’ve combed the data on the G3X data card after every flight and all that is there is the A/P fail messages. No other data aberrations that would have contributed to the failure. No indications of GPS faults either. I haven’t looked at the G5 data but I’ll do that tomorrow. I do have an SD card in the G5 but I never look at it. As for the airspeed trend indicator, Barry has seen it without the autopilot engaged (the pic in my first post) but I have not.

Also, both airplanes here have had recent pitot static checks and are good.

We’re both going to concentrate on watching what the G5 is doing on our next flights. Barry is going up tomorrow, and I have a trip on Monday.

[PT20J]

What does the airspeed tape do on the standby instrument when the G3X is acting up? If it’s not doing the same thing, I would suspect a GSU 25D issue.

You could try pulling the GSU CB the next time it happens which will disconnect the GFC 500 and cause the G3X to revert to the standby ADAHRS (G5 or GI 275) to see if everything then operates normally. Be aware that if your installation is wired per the STC you will lose the magnetometer and the G3X HDG indication will drift or may revert to TRK. This is because the STC has both the magnetometer and the GSU 25D on the same CB. (I talked my installer into a minor mod to put them on separate breakers).

This may not be a bug - it may be an intermittent GSU. If it works on the standby ADAHRS, I would just replace the GSU 25D.

The GFC 500 AFMS describes the flashing annunciations here:

 

[EricJ]

The more I fly airplanes with Garmin autopilot systems the quirkier they seem.   I just flew a C182 with an NXi G1000 with ESP and it did some really weird stuff, and I'm used to C182s with the older G1000, non-NXi, systems (and they're quirky enough on their own).  The guy I was flying with owns an Arrow with a GFC500 and ESP and says it behaves differently in his airplane.   His does pitch oscillations just like the Mooneys do, too.

I'm sure it's an engineering problem at Garmin to try to mix and match all of the possible different box configurations that the various systems have to deal with to try to still integrate successfully, but it does seem like they aren't sufficiently hitting the corner cases in the regression testing.   If an issue is hard to reproduce or the fix in one application will interfere in another, it may just get deprioritized.   This stuff just comes up often enough that I really wonder about how smoothly the product integration and update gears mesh at Garmin.

[Rick Junkin]

39 minutes ago, PT20J said:

What does the airspeed tape do on the standby instrument when the G3X is acting up? If it’s not doing the same thing, I would suspect a GSU 25D issue.

You could try pulling the GSU CB the next time it happens which will disconnect the GFC 500 and cause the G3X to revert to the standby ADAHRS (G5 or GI 275) to see if everything then operates normally. Be aware that if your installation is wired per the STC you will lose the magnetometer and the G3X HDG indication will drift or may revert to TRK. This is because the STC has both the magnetometer and the GSU 25D on the same CB. (I talked my installer into a minor mod to put them on separate breakers).

This may not be a bug - it may be an intermittent GSU. If it works on the standby ADAHRS, I would just replace the GSU 25D.

The GFC 500 AFMS describes the flashing annunciations here:

 

Thanks Skip, I missed the paragraph in the AFMS. The GSU 25 is my number one suspect for both airplanes. My trip Monday is to my avionics shop for some other minor stuff so I may ask him if he’ll do a warranty swap on the GSU 25 as the most likely cause. Of course that will require a call to Garmin for approval, so who knows.

[Pinecone]

WRT to autopilot disconnect, Garmin is saying mine may be due to GPS issues.  My #1 is reporting 3D- (column H in log ), instead of the desired 3DDiff.

Avionics shop it thinking antenna issue.  One antenna is from 2017, GTN-650 install.

But, I had been running the Service Bulletin revised gains to deal with pitch oscillations.  So my shop thought we should try to go back to the original STC gains.  When they did this, they noticed (they always check the lasted revisions from Garmin's site) that they changed.  So now we have the Original Gains, the SB Gains, and the Current Revised STC Gains.

Putting in the Current Revised gains, I have slight pitch oscillation, that it acceptable, but my AP disconnects have pretty much gone.  I got on on climb out on my first trip after the change, but then flew almost 18 hours without a single hiccup.

[Fly Boomer]

On 11/23/2024 at 6:07 PM, EricJ said:

but it does seem like they aren't sufficiently hitting the corner cases in the regression testing

I haven't counted them, but it feels like I have read a hundred topics on this forum about the GFC-500 misbehaving in some fashion.  I wonder if the 600s and 700s are plagued with similar issues.

[Rick Junkin]

On 11/24/2024 at 7:00 PM, Pinecone said:

WRT to autopilot disconnect, Garmin is saying mine may be due to GPS issues.  My #1 is reporting 3D- (column H in log ), instead of the desired 3DDiff.

Avionics shop it thinking antenna issue.  One antenna is from 2017, GTN-650 install.

But, I had been running the Service Bulletin revised gains to deal with pitch oscillations.  So my shop thought we should try to go back to the original STC gains.  When they did this, they noticed (they always check the lasted revisions from Garmin's site) that they changed.  So now we have the Original Gains, the SB Gains, and the Current Revised STC Gains.

Putting in the Current Revised gains, I have slight pitch oscillation, that it acceptable, but my AP disconnects have pretty much gone.  I got on on climb out on my first trip after the change, but then flew almost 18 hours without a single hiccup.

What I want to see is something from Garmin describing what they did to address the problem, rather than an apparent stealth update to the STC gains with no information about what changes they made or why they made them.

My shop is a Platinum Garmin dealer/installer and I’m going to be visiting them today and tomorrow. I’ll report back with anything I learn while I’m there.

EDIT: The shop has no experience with the issues I'm having but they agree its most likely an intermittent air data problem in the GSU 25. So they're swapping in a new one for me under warranty. We'll see if that does the trick.

Oh, and of course the A/P was rock solid through hard IFR and moderate turbulence all the way here, a 1.3 hour flight.

[Pinecone]

Remember, you only hear about issues, not from those without any issues.

[Ryan ORL]

I have had a handful of GFC500 uncommanded disconnects in the last 2 years since I had it installed, on average this happens like... once every 50 flight hours?  It's pretty rare but does happen.  (I just re-engage and it doesn't happen again)  But when these happen, I have never seen the HDG PIT annunciations you're showing there.

I also did have a GSU25 failure (under warranty) right when I first got my G3X, but it didn't behave like this.  It was more like a total failure, the attitude went absolutely wacky for a few seconds and then (if I recall correctly) I got some AHRS failure messages and it went to the G5 standby AHRS.

[hubcap]

I have ~200 hrs on my GFC 500. It has never disconnected unintentionally.

[ArtVandelay]

I have ~200 hrs on my GFC 500. It has never disconnected unintentionally.

I did, it was always in an aggressive attitude, but that was a few years ago. First thing I would do is have all the software updated.

[Marc_B]

3 hours ago, hubcap said:

I have ~200 hrs on my GFC 500. It has never disconnected unintentionally.

+1.  I've flown 260 hrs on mine in almost 2 years with original servos, original gain settings, and haven't had any issues at this point.  My shop usually does a good job of keeping my software updated, for what that's worth, so I'm likely on the most current SW version.

[Rick Junkin]

I keep my software up to date. I’m running v9.18 in the G3X along with all of the associated component software updated with the release of 9.18.

I learned today that there are several different part numbers for the GSU 25D. My shop today swapped my original GSU 25 part number 010-01071-56 for the most recent GSU 25 part number 011-02929-56. I don’t know what was changed, but I remember reading about it when the new part came out. There was an SB for it I believe.

At any rate the GFC 500 was solid from departure all the way through a coupled RNAV approach I let go almost to the runway. VFR of course. But it was a short 1.5 hour flight. I’ll see how it does on my next 2+ hour trip.

[PT20J]

3 hours ago, Rick Junkin said:

I keep my software up to date. I’m running v9.18 in the G3X along with all of the associated component software updated with the release of 9.18.

I learned today that there are several different part numbers for the GSU 25D. My shop today swapped my original GSU 25 part number 010-01071-56 for the most recent GSU 25 part number 011-02929-56. I don’t know what was changed, but I remember reading about it when the new part came out. There was an SB for it I believe.

At any rate the GFC 500 was solid from departure all the way through a coupled RNAV approach I let go almost to the runway. VFR of course. But it was a short 1.5 hour flight. I’ll see how it does on my next 2+ hour trip.

I’ve never quite figured out Garmin’s part numbering system. My GSU 25D is listed on the invoice and in the logbook entry as a 011-02929-51. But, in the warranty records, it’s listed as a 010-01071-51. In most configuration management systems, the first digits denote the level of assembly. So I assume that the 010-number is the basic part and the 011-number includes the basic part plus whatever ancillary components are necessary to complete the installation, but I’m not certain. Also, the last part of the number would likely be the version. The 011-02929-56 was supported beginning with G3X version 9.00. I have no idea what the difference is between a -51 and a -56 but it must have required a software change. 

[Rick Junkin]

7 hours ago, PT20J said:

I have no idea what the difference is between a -51 and a -56 but it must have required a software change. 

I ran across something that led me to believe the -56 vs -51 has to do with altitude/environmental capability but that didn’t make much sense to me. I was surfing specs across multiple sites and unfortunately don’t remember where I saw that.

So basically this is a useless post 

[Pinecone]

I just checked, my plane, which is also having some AP issues does have a 011-0292-56.

[PT20J]

3 hours ago, Rick Junkin said:

I ran across something that led me to believe the -56 vs -51 has to do with altitude/environmental capability but that didn’t make much sense to me. I was surfing specs across multiple sites and unfortunately don’t remember where I saw that.

So basically this is a useless post 

Maybe not useless. It caused me to look in the G3X Experimental Installation Manual. -51 is rated to 30,000 ft, and -56 is rated to 55,000 ft.

[Rick Junkin]

3 hours ago, Pinecone said:

I just checked, my plane, which is also having some AP issues does have a 011-0292-56.

My hangar neighbor Barry with the Bo that's having the same issue also has the 011-02929-56 installed. His installer told him this morning that the Garmin rep he works with is adamant that they are working on a software fix for the exact issue he and I are having. So it could be that my new GSU 25D won't make any difference, and I just haven't exercised it enough to precipitate the failure. However if my airplane doesn't act up again, Barry's installer has agreed to replace his on warranty too.

It's really puzzling how the majority of installations are trouble-free but the installations with issues have the same or very similar issues. And it really surprised me that Barry's Bo and my Mooney have exactly the same issue. I'm guessing the Garmin engineers are scratching their heads as well. From my work experience with a major aerospace company, I'd surmise the head scratching is either because they can't determine a root cause or because management won't allow them to address the root cause for these one-off cases. There, that's my conspiracy theorizing for the day. Besides, the Garmin field rep says they are working on a software fix. Should be any day now. Yup, any day. 

[PT20J]

Garmin engineers have supposedly been looking for over a year at an issue I sent them (with a lot of data) where the G3X does not display all TFRs that are active and displayed on my GTN. Both the GTN and G3X receive ADS-B IN from the GTX 345. I suspect it is related to an earlier problem where multi-day TFRs were only displayed on the first day on the GTN which required software updates for the GTX and GTN. 

[jamesm]

Not sure If this helps... Nor am I familiar with the relationship between G5 and G3x display (other than I am guessing it's some CAN interface) to GFC500 autopilot connection. I have '67C 2 G5's and GNC255&355/GNX375 GFC500. I  use to and quite regularly get the yellow "HDG" display indication this what would happen to me before the GFC 500 was installed.  I had the 2 G5 configuration. where the HSI  on take off on it's own  it would revert to  ADI display. you could manually change it back but this was a new failure to me. This told me that something is wrong and at the time I was planning on having the  GFC500 installed. I had been getting the Yellow  high lighted "HDG" indication since it was installed 2018. I had tried what Garmin  prescribed to me in Late 2020  below before the A/P was installed  with no avail. So I figured that during the A/P install that they would be  going through the wiring catch what ever was wrong.  As turn out after the GFC500 was installed  the A/P would disconnect on it's own. So I took back to Avionics place they swapped the ADI with HSI A/P functioned correctly no A/P disconnects. So my original G5 ADI had intermittently failed.  I could see failure  in the G5 SD card log files.  The avionics installer had the G5 ADI exchanged for me and I reconfigured the ADI/ HSI back to original configuration but the "new" G5 was failing as well. So Garmin  sent me a reconditioned G5 unit that finally fixed it.  until about 3 months ago the  HSI was reverting to ADI on it's own again.  This time no obvious  trace in the G5 SD log file of the failure. The avionics installer updated the software but still no avail. the Avionics installer  claimed that they open all the connectors reassembled them and re-calibrated magnetometer. No yellow "HDG" indication and  no A/P disconnects  so far all is good.

So it seems like are there similar failures from the Pilot/human interface prospective but at the avionics end different issues causing the problem(s). A bit suspicious of Garmin's avionics spares inventory tracking and quality control ability. Having gone through it with G5 and  I had similar go around with GNC355 TX gain  setting  issue that would dump when it was powered off.  Once powered the GNC355 back on and then no one could hear me transmit. you wouldn't necessarily catch this issue depending on the airspace you fly in. I spoke with one of the engineer's he acknowledge that this was a known issue with the GNC355's but only "few" of the early S/N  units. My dumb luck I had gone through two of them before it was finally resolved. I believe that there was a software fixed this. 

It sucks paying out all this money a not having trust and  having reliability issues in our A/P's and avionics.

I hope they find the source of them problem and find a solid fix for it.

James'67C

 

 

[Rick Junkin]

Wow. Makes me wonder how many other folks have the same/similar issues with the dual G5 lash-up. Sorry to hear of your trials. All of these issues are safety of flight issues. I’m wondering why nothing has been released to restrict using this gear for IFR. Not that I want a formal restriction. But they did put out the restrictive SB (AD?) for the runaway trim problem a year or two ago. What’s the threshold?

I forgot to pull the G5 data card Tuesday  so I’ll have to wait until tomorrow when I’m at the hangar to see what that data reveals. With the G3X and GSU25 operational I don’t believe the GFC 500 is polling the G5 for any data but that’s a guess on my part.