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My pitch oscillation problem has still not been resolved, although Garmin is working on the problem.  They are pretty certain that it is something related to the installation because they have always found that to be the case in the past with installations in other types of aircraft.  I asked them about Mooney installations and they said that they have sold quite a few Mooney GFC 500s.  When I asked them if they know of any that had been completed other than mine they didn't know, but said people don't complain if things are working.  So I am asking if anyone here has done the installation in an M20M (other than Andy, whose plane was used to get the G500 certified in the M20M), and whether their's works perfectly--especially in the pitch axis.

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31 minutes ago, Jesse Saint said:

I hate to say his, but Garmin has been known to say they’ve never heard of this problem before while they are working on a fix from other reports of the same problem. 

After sending them all my data and their having reviewed it, they want me to stop by Olathe next week on my way to Oshkosh to see if they can locate the problem.  One way or other this problem is going to get fixed.

Again, let me say, having flown the GFC 500 for 20 hours, it really is a fantastic autopilot with so many more features than the KFC 150.  Obviously it's made to interface with all the other Garmin products, and the way it interfaces with the G500 TXi and it with the G5 cuts pilot workload tremendously.  I especially like the yaw damper and, once you figure it out, the VNAV function. 

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1 hour ago, thinwing said:

Haven’t you had a pitch oscillation problem before ,even with old autopilot?

No.  With the KFC 150 it was a 1°-2° Roll problem that occurred anytime the plane was put into HDG, NAV or APR.  It was perfect in GPSS mode.

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On 7/5/2019 at 12:13 PM, donkaye said:

My pitch oscillation problem has still not been resolved, although Garmin is working on the problem.  They are pretty certain that it is something related to the installation because they have always found that to be the case in the past with installations in other types of aircraft.  I asked them about Mooney installations and they said that they have sold quite a few Mooney GFC 500s.  When I asked them if they know of any that had been completed other than mine they didn't know, but said people don't complain if things are working.  So I am asking if anyone here has done the installation in an M20M (other than Andy, whose plane was used to get the G500 certified in the M20M), and whether their's works perfectly--especially in the pitch axis.

Garmin used my K for certification and I have no oscillation issues.  That said, when do you get pitch oscillations?  Not that you should have to, but for troubleshooting purposes, have you tried engaging the AP after you’re established in cruise and manually trimmed out?

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2 hours ago, 81X said:

Garmin used my K for certification and I have no oscillation issues.  That said, when do you get pitch oscillations?  Not that you should have to, but for troubleshooting purposes, have you tried engaging the AP after you’re established in cruise and manually trimmed out?

Does your plane roll out on heading or short of it and then takes some time to get to the set heading?  That is one of my problems.  The other, the pitch oscillation, can easily be demonstrated by doing a turn greater than about 20°.  In level flight it happens randomly.  I'm looking forward to my stop in Olathe at Garmin on the way to Oshkosh this coming week to have them analyze the problems and come up with a fix for me.

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6 hours ago, donkaye said:

Does your plane roll out on heading or short of it and then takes some time to get to the set heading?  That is one of my problems.  The other, the pitch oscillation, can easily be demonstrated by doing a turn greater than about 20°.  In level flight it happens randomly.  I'm looking forward to my stop in Olathe at Garmin on the way to Oshkosh this coming week to have them analyze the problems and come up with a fix for me.

I’m going to go out and fly it today so I’ll check those flight regimes, but I’m pretty sure that there are no pitch oscillations on large turns.  As for the roll out, I usually get a roll out within a degree or two of bugged heading and I haven’t noticed excessive time to nail the exact number but I will report back. 

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16 hours ago, donkaye said:

Does your plane roll out on heading or short of it and then takes some time to get to the set heading?  That is one of my problems.  The other, the pitch oscillation, can easily be demonstrated by doing a turn greater than about 20°.  In level flight it happens randomly.  I'm looking forward to my stop in Olathe at Garmin on the way to Oshkosh this coming week to have them analyze the problems and come up with a fix for me.

Do you have some short, clear videos ready to show them so they can see the pitch and roll/heading issues? If a picture is worth a thousand words, a video is priceless.

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37 minutes ago, Ragsf15e said:

Do you have some short, clear videos ready to show them so they can see the pitch and roll/heading issues? If a picture is worth a thousand words, a video is priceless.

These videos that I sent them are the reason they want to see me. There is a 6 minute video showing the heading and pitch issue.  It was a little bumpy when I did the video.

https://drive.google.com/file/d/10Siqaby2krDABL6ehE3Irdj8IoQ0BEid/view?usp=sharing

Here is another one showing the pitch oscillations.

https://drive.google.com/file/d/1-CIaywxdDvwiy_RGqkOGoysPc8VlNZ0X/view?usp=sharing

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Don I know you have all new servos etc with the new a/p. When my J was new I had a KFC 150 I think, anyway I had pitch issues like you depicted, after numerous attempts to fix the issue including changing the computer a few times, my avionics shop changed the pitch servos and the issue resolved, I had similar issues with the Bravo Stec55X and it was also the servos. Hopefully the company in Olaithe with figure it out. 

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12 hours ago, 81X said:

I’m going to go out and fly it today so I’ll check those flight regimes, but I’m pretty sure that there are no pitch oscillations on large turns.  As for the roll out, I usually get a roll out within a degree or two of bugged heading and I haven’t noticed excessive time to nail the exact number but I will report back. 

Unfortunately I didn’t get to mess with it today as I had to skip town.  What I do know is that the Olathe and Salem crews are top shelf.  

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52 minutes ago, carqwik said:

The second video is kind of scary...do the pitch oscillations get worse at higher altitudes?

Once it gets started it seems about the same at any altitude.  Notice that the autopilot was on ALT when all of this happens.

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How does it do in vertical nav modes? Still have oscillations during a VNAV path (I think your setup can do that mode) or IAS mode?  What happens if you set VS to say, 20?. 

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On 7/13/2019 at 9:42 PM, donkaye said:

Does your plane roll out on heading or short of it and then takes some time to get to the set heading?  That is one of my problems.  The other, the pitch oscillation, can easily be demonstrated by doing a turn greater than about 20°.  In level flight it happens randomly.  I'm looking forward to my stop in Olathe at Garmin on the way to Oshkosh this coming week to have them analyze the problems and come up with a fix for me.

Check the magnetometer installation and/or the AHRS.  Usually that is the issue with these.  It is imperative that they be installed correctly.  However, pitch oscillations are generated generally from the AHRS as there  is no VG in these systems.  Would love to help Don

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For any early M20J owners out there (serial numbers 24-0001 through 24-1037, Garmin this morning approved Installation Bulletin 1954 Rev A which describes how to modify and install the roll servo lower bracket and roll servo plate so it will fit properly in those aircraft as they have internally mounted access panels.  This is what I was waiting for to get my GFC-500 install completed.  Can't wait to fly it!

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  • 2 weeks later...
On 7/15/2019 at 8:30 AM, donkaye said:

Sometimes it oscillates during Approach and VNAV modes and sometimes it doesn't.

Don, you have my number, give me a call and let me know what you find out please and if you need a hand, I will gladly help out with the repair/solution for nothing just to get this right for you.  I am not saying your support is not good, just wanting to help out the situation.  

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Thank you, Greg, I'll let you all know the results after my 8 hour flight back to the Bay Area over the next few days.  The problem may be resolved.  The next 8 hours will tell.

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Well not a long body like Don's but the install in my M20J is complete and I picked the plane up on Friday and it works flawlessly.  I've flown 7.5 hours with it since and I'm incredibly impressed.  It flies the plane very smoothly and accurately.  I have flown 6 approaches now and they were all perfect, even with strong winds and bumpy air.  While I still have a lot to learn about how to use it to it's fullest, I am thrilled with everything I've experienced so far.  It is worlds better than the 55x it replaced.  Also, I have nothing but great things to say about Garmin's support given the issues the shop had with the roll servo brackets that needed to be modified and approved.  Garmin got it all done in 2.5 weeks and came by the shop to fit the modified bracket and test it in place in order to expedite the approval.

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Not a GFC and not sure how it does altitude hold but certainly looks like a pressure transducer issue you would see in a S-TEC when they go bad (or there is water in the static lines). 

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I've waited until I had put some time on the GFC 500 after my problem was analyzed and corrected before I posted.  I now have 6 hours with it and am able to confirm that my pitch oscillation problem is apparently and thankfully resolved.

I can't say enough about the fabulous support given this issue by Garmin and their support team.  While there were many people involved whose names I don't know, two that were absolutely integral to defining and implementing the solution were Trek Lawler and Aaron Newman.  From the beginning Trek said from his experience this type of problem was usually an installation issue.  He was right once again.  For whatever reason, the pitch trim servo was not properly braced per the STC, and three setting were not correct.  Once these items were corrected, I have an autopilot that both meets and exceeds my expectations.

In the last six hours there has been no oscillations, and the flights have been mixed with smooth and bumpy air.  Shirley really notices the difference, especially in turbulence.  In the past with the KFC 150 it has been necessary to turn off the autopilot in rough air.  Not so so far with the GFC 500.  Where the KFC 150 would overshoot the level off after altitude capture, the GFC 500 smoothly captures right on the altitude preselected.  It's like I'm flying a different airplane.

Many threads have been talking about many different new autopilots from different manufactures.  Some have been approved, and some are awaiting approval.  I read many of the reports and am not impressed.  Notwithstanding the GFC 700, the GFC 500 is now the best autopilot I have flown.  The only item I wish Garmin had included was CWS, but its lack of implementation has not be a hardship.

Yes, I went all in for nearly every Garmin Aviation product on the market.  This autopilot on my airplane confirms that decision.

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