GFC500 problem

[rbp]

Sent to @TrekLawler today:

 

Hi Trek —

My plane is going in to SureFlight this week, where Chris is going to be looking at the GFC oscillations in IAS and VNAV modes. These modes are UNUSUABLE for me.

Note that I have tried alternate static and the controls/yoke, etc were lubed at the last annual.

There are still a lot of people on MooneySpace ( https://mooneyspace.com/topic/42115-gfc500-problem  )having problems, and folks are cross-referencing similar issues on BeechTalk viz vibration ( https://youtu.be/WEf73kRPOLE ) and the fact that there are different servos on the 600.

I’m wondering where all of this is going, and what Garmin’s plan is to get to track all of these issues and get to the bottom of them

—Bob

 

[rbp]

Update from avionics shop on my GFC500:

There was a big leak in the static system back at the port at 8000 feet, leak is now under 100 feet from 2400. This is what fixed the last Mooney that has the same issues. We are only required to leak check at 1000ft, but Garmin has now said make it good to 8000 ft or issues could occur.

Hopefully this will fix the problem.

 

 

[ArtVandelay]

Update from avionics shop on my GFC500:
There was a big leak in the static system back at the port at 8000 feet, leak is now under 100 feet from 2400. This is what fixed the last Mooney that has the same issues. We are only required to leak check at 1000ft, but Garmin has now said make it good to 8000 ft or issues could occur.
Hopefully this will fix the problem.
 
 

How does pressing on the panel stop the leak if that’s the problem?

[rbp]

On 12/5/2022 at 9:06 PM, rbp said:

Update from avionics shop on my GFC500:

There was a big leak in the static system back at the port at 8000 feet, leak is now under 100 feet from 2400. This is what fixed the last Mooney that has the same issues. We are only required to leak check at 1000ft, but Garmin has now said make it good to 8000 ft or issues could occur.

Hopefully this will fix the problem.

 

 

So I visited the avionics shop today and did a test flight after they had fixed the static port leak mentioned above.

IAS oscillations are still occurring. 

Here are two videos I made of IAS and VS modes

IAS mode @120KIAS 

 

VS mode @800FPM 

 

 

[PeytonM]

Do you observe oscillations in ALT mode?

[rbp]

1 hour ago, PeytonM said:

Do you observe oscillations in ALT mode?

Just IAS.
 

Since they have fixed the static put leak,  I’m now wondering if there’s a problem with the pitot,

[PT20J]

There is a pitot leak test in the service manual. Basically, you pressurize the pitot by some means (rolled up rubber tube, or I used a large syringe with a short piece of tubing attached -- just make sure your apparatus doesn't leak) to 150 KIAS and make sure it doesn't leak more than 10 kts in one minute. But, I doubt that's your problem.

I notice that your video begins with airspeed about 117 KIAS but the set airspeed is 120 KIAS. I have noticed that my GFC 500 tends to hunt a bit in IAS, but in smooth air it will eventually settle down when it wearies of chasing the phugoid. I would try setting up a steady climb in PIT and when the airspeed is stable then engage IAS and see if it holds the set speed or begins to oscillate. If it is steady, put the gear down which will excite the phugoid and see how well it tracks IAS. In my M20J the phugoid damps out within three cycles and the period is about 30 seconds.

I notice a couple of interesting things in the video. First the flight director commands appear to be reacting primarily to the rate of change of airspeed leading to some pretty aggressive pitch commands, and second the pitch sometimes lags the command bars significantly. There might be a clue here. I would send the video to Trek.

Skip

 

 

 

[ArtVandelay]

I had a pinched pitot tube that caused issues with IAS, definitely need to check this.

[LANCECASPER]

On 12/14/2022 at 5:08 PM, ArtVandelay said:

I had a pinched pitot tube that caused issues with IAS, definitely need to check this.

that sounds painful

[rbp]

On 12/13/2022 at 9:46 PM, rbp said:

So I visited the avionics shop today and did a test flight after they had fixed the static port leak mentioned above.

IAS oscillations are still occurring. 

Here are two videos I made of IAS and VS modes

IAS mode @120KIAS

VS mode @800FPM 

Here's the graph of the EIS data collected during the flight 

[rbp]

I don’t have any improvement to report, but I do have some encouraging news

1.  I have finally accepted that the installer is never going to expend the energy to fix this. They have dragged their feet, refused to engage resources at Garmin, and are silent on what troubleshooting steps they have taken.  Last time I spoke with them, they blamed the trim servo SB.  Sean at C&W is going work on it and he is already engaged.

2. Garmin has said that they have seen the issue in numerous mooneys, and that airframe issues (lubrication/friction, tension, mounting, and pitot/static) and miscalibration have been the culprits, and some shops have not been sufficiently thorough frustrating owners and requiring multiple trips to the shop  

3. The GFC experts have analyzed my G3X logs, and can clearly see the issue. They have sent me and Sean a troubleshooting procedure that covers all the items above and have made themselves available to help.

based on this, I think there’s a gremlin in the install, not a systemic or cerification   (gain) issue 

Plane goes to C&W ~Jan 16

i am once again optimistic 

if it gets fixed in the field, it means that anyone wanting a GFC500 should be very selective in who does the install, and to make sure the shop is committed to following the procedures exactly and working closely with Garmin 

[rbp]

From Garmin based on G3X logs 

 

[rbp]

On 12/14/2022 at 10:56 AM, PeytonM said:

Do you observe oscillations in ALT mode?

Curiously, Garmin found that ALT mode has oscillations that I didnt detect 

 

[PeytonM]

As I indicated in my previous posts, I have the alt oscillations. They are small, 5-10 feet. I too have sent logs to Garmin and they have verified the issue. (Btw, if I take the A/P off of Alt, which puts the A/P in Pitch mode, it immediately smoothes out! You might try that as an experiment.)

Garmin sent 4 gents down to look at the installation and my airframe and determined everything was fine. I am confident that Garmin will get to the bottom of this. Both Garmin and my installer have been responsive and supportive (and are equally frustrated.)

[Fly Boomer]

2 hours ago, rbp said:

I don’t have any improvement to report, but I do have some encouraging news

1.  I have finally accepted that Sureflight (in Coatesville PA) is never going to expend the energy to fix this. They have dragged their feet, refused to engage resources at Garmin, and are silent on what troubleshooting steps they have taken.  Last time I spoke with Sureflight, they blamed the trim servo SB.  Sean at C&W is going work on it and he is already engaged.

2. Garmin has said that they have seen the issue in numerous mooneys, and that airframe issues (lubrication/friction, tension, mounting, and pitot/static) and miscalibration have been the culprits, and some shops have not been sufficiently thorough frustrating owners and requiring multiple trips to the shop  (which seems to be my  issue at Sureflight),  

3. The GFC experts have analyzed my G3X logs, and can clearly see the issue. They have sent me and Sean a troubleshooting procedure that covers all the items above and have made themselves available to help.

based on this, I think there’s a gremlin in the install, not a systemic or cerification   (gain) issue

Plane goes to C&W ~Jan 16

i am once again optimistic 

if it gets fixed in the field, it means that anyone wanting a GFC500 should be very selective in who does the install, and to make sure the shop is committed to following the procedures exactly and working closely with Garmin 

I wonder if anyone had ongoing issues like these with a KFC-150 when they were newer -- even 20 years ago?  Now, the KFC-150 is old and tired, but all these Garmin issues are on fairly new equipment.
 

[LANCECASPER]

1 hour ago, Fly Boomer said:

I wonder if anyone had ongoing issues like these with a KFC-150 when they were newer -- even 20 years ago?  Now, the KFC-150 is old and tired, but all these Garmin issues are on fairly new equipment.
 

In 1996 I bought a Bravo from Mooney. Soon thereafter the altitude hold on my KFC150 wouldn’t hold but the course would. Bendix King overnighted a KC192 control unit down for me to use as a loaner while they fixed mine. Thankfully it was under warranty. The loaner worked perfectly. When I got mine back on the first flight it would fail. I went through this three times before I wrote to Bendix King explaining that I wouldn’t be returning their loaner and that they could keep mine and to please change the serial number in my records and that my mechanic would do the same in my logbooks. I never heard another word and it worked perfectly from that point on. Other than that the KFC150s that I had were rock solid - others have had problems with theirs’. But in its day that was the top of the line for GA. I felt like I was flying an airliner when I’d set the pre-select and later watch it level off. If it’s only worked on by experts, and there are just a few now left in the country, they were great and had a long service life.

[whiskytango]

5 hours ago, rbp said:

3. The GFC experts have analyzed my G3X logs, and can clearly see the issue. They have sent me and Sean a troubleshooting procedure that covers all the items above and have made themselves available to help.

@rbp is the Garmin troubleshooting procedure available to any Mooney owner experiencing pitch oscillation in their new GFC500 installation?  

[rbp]

There doesn’t seem to be any proprietary notice on it, so here goes. 
 

im also copyin here the notes specific to my airframe 

———-

IAS Mode issues are more related to pitot issues instead of static pressure. We’re hoping this was checked as well however It wouldn’t hurt to have the pitot tube checked for blockages or a rough or damaged leading edge. As you can see from the first graph below this is varying quite a bit.

There is almost a constant motion on the pitch servo…as if it is hunting through a dead spot caused by loose cable tension or excess friction.

We need to have the cable tension checked and would like to have these findings sent to us using an appropriate tensiometer, not just “they are good” by feel. The reason we really hound on this is we recently looked at a plane that the dealer indicated they had checked only to look at it ourselves and find that the tensions were way off using our calibrated meter.

We recommend also that all Config settings get verified and are set to what the latest Gains addendum states.

AP Troubleshooting Checklist.rtf.pdf

[rbp]

I brought 54x into C&W and they started working on it yesterday. Even after multiple visits to the installer didn't fix all the problems. C&W has found pitot and static leaks that they are going to fix before moving on to item 8 in the checklist: "Pitot/static excessive leak rates (perform hi-level leak test @ 15K’)". C&W (unlike the installer) are collaborating with the folks at Garmin.

Stay tuned!

[carusoam]

Nice work rbp!

Your data collection skills are top notch!

Best regards,

-a-

[rbp]

So more data -- it turns out that the bridle cable tensions are either out of spec or at the bottom. Garmin is recommending that they be tightened to near the top of the range because the cables will stretch and be affected by temperature changes at altitude. 

At one point in time I believed that there might be a problem with the settings (ie gain) or some software problem, but I have come full circle and believe the issues to be directly attributable to workmanship in the installation

 

[rbp]

The pitot leak was fixed and the bridle tensions were tightened, so I did a short test flight today, and the IAS oscillations  remain.

here's a climb from 2500 to 5500'. you can see how the IAS varies from about 113 to 126. the pitch up and down was quite dramatic and I had my finger on the AP disconnect the whole time

next step is to send the logs to @TrekLawler

[LANCECASPER]

45 minutes ago, rbp said:

The pitot leak was fixed and the bridle tensions were tightened, so I did a short test flight today, and the IAS oscillations  remain.

here's a climb from 2500 to 5500'. you can see how the IAS varies from about 113 to 126. the pitch up and down was quite dramatic and I had my finger on the AP disconnect the whole time

next step is to send the logs to @TrekLawler

How does it do when you climb based on vertical speed, i.e. 500 fpm?

[rbp]

2 minutes ago, LANCECASPER said:

How does it do when you climb based on vertical speed, i.e. 500 fpm?

solid as a rock

[LANCECASPER]

5 minutes ago, rbp said:

solid as a rock

I think you're chasing something you won't catch. I'm new to the G1000 with a GFC700 (a little over a year) - everyone I talked to before I bought the airplane said that its great at VS climbs but you won't like IAS climbs. I believed them and I climb based on VS.