GFC500 Oscillation Poll

[mike_elliott]

In speaking with 3 Mooney owners at the Florida Mooney Lunch Group today that had GFC500 Installed in their planes, It came to light all 3 were experiencing pitch oscillations with their AP. Some have tried to adjust gain out of STC spec to resolve with a small degree of improvement, others are at loss saying their shop has basically said its out of their hands. Is this problem a pattern for Mooneys or an issue of 3 different shops installing incorrectly? The time I have had behind the GFC500 has not displayed the issue, but admittedly, that time is far less extensive compared to what I have behind the best in class GFC 700. From what I can gleen, it is probably more of a software thing with sensors, perhaps timing of trim actuation than that of hardware failure, but admittedly, just really beginning to dive into the reported issue. If anyone has had this issue and has a definitive fix, please post.

[PT20J]

Mike, you left out the J

Also, voting in the first question requires an answer to the second which I don’t believe is what you intended.

[mike_elliott]

opps, I am a student at this poll thingie...fixed the J issue caused by old age THanks Skip

 

[rbp]

@Tom 4536 @thomas1142 @Evan @Mooney in Oz @PeytonM @TrekLawler

Hey J + K folks -- Mooney is looking to bring a J/K model into Garmin to work on the GFC500 oscillations. Are any of you willing to consider? 
 

[Tom 4536]

My plane is going in for an annual at Chandler Aviation (MSC) if Garmin wants to look at the plane while it is apart.

[rbp]

3 minutes ago, Tom 4536 said:

My plane is going in for an annual at Chandler Aviation (MSC) if Garmin wants to look at the plane while it is apart.

I think they want one at the factory. Did you get Garmin's GFC500 troubleshooting checklist? 

[Tom 4536]

I think I did but can you provide a link so that I can review it. A family emergency has kept me from even thinking about flying or anything airplane.

[rbp]

18 minutes ago, Tom 4536 said:

I think I did but can you provide a link so that I can review it. A family emergency has kept me from even thinking about flying or anything airplane.

There's no Garmin link, just a PDF. It's from Dec. Not sure if they're a later one.  

 Troubleshooting Checklist.pdf

[Mooney in Oz]

18 hours ago, rbp said:

@Tom 4536 @thomas1142 @Evan @Mooney in Oz @PeytonM @TrekLawler

Hey J + K folks -- Mooney is looking to bring a J/K model into Garmin to work on the GFC500 oscillations. Are any of you willing to consider? 
 

I’d love to, but I’m in Australia 

[rbp]

1 hour ago, Mooney in Oz said:

I’d love to, but I’m in Australia 

how did your plane get there?

 

[rbp]

1 hour ago, Evan said:

I'd be willing to bring mine. It doesn't nearly have the bad oscillations that some here do but would be great if they looked at it. They clearly are noticing there is an issue. 

excellent! can you DM me your email address and I will make the connection 

[81X]

For me- it depends on the vertical mode- 

Alt hold- rarely oscillates but I have noticed a little oscillation in very smooth air.  Funny things is I never noticed this for the 2-3 years when it was driven by the G5, I only noticed it after I got a G3X. Maybe I just didn’t notice visually earlier looking outside or at the smaller G5 screen.  
 

VS mode- nothing noticeable 

 

IAS climb- seems to hunt for the airspeed which materializes as annoying pitch oscillations.  
 

M20K 231. 

[PT20J]

40 minutes ago, 81X said:

IAS climb- seems to hunt for the airspeed which materializes as annoying pitch oscillations.  

Does it hunt continuously, or just when changing airspeeds?

Mine wasn’t bad and only in IAS and only when engaging with the speed bug different than current speed or changing the bug rapidly away from current speed. Tightening the pitch bridle fixed it. Discussed with Trek and Garmin recommends setting tension to the max during installation and rechecking after a year as the cables can stretch a bit as the strands take a final set in service. 

[rbp]

they tighened mine up. I will bring it to C&W and ask them to give it another 1/2 turn and do a test flight

[81X]

2 hours ago, PT20J said:

Does it hunt continuously, or just when changing airspeeds?

Mine wasn’t bad and only in IAS and only when engaging with the speed bug different than current speed or changing the bug rapidly away from current speed. Tightening the pitch bridle fixed it. Discussed with Trek and Garmin recommends setting tension to the max during installation and rechecking after a year as the cables can stretch a bit as the strands take a final set in service. 

More or less continuously if in turbulence, but it’s not as continuous in smooth air.  

[rbp]

4 hours ago, 81X said:

More or less continuously if in turbulence, but it’s not as continuous in smooth air.  

Even when you adjust the target airspeed with the wheel?

[PeytonM]

The threads on porpoising have quieted. I wonder if folks have found a solution or just given up. Reports on BT persist. 

[hubcap]

I have ~70 hours with my GFC500 since getting Myrtle back at the end of April. I have not experienced any porpoising. It has been rock solid. 

[Rick Junkin]

During my research into this oscillation issue I came across this Garmin service bulletin for gain adjustments on SR22 GFC500 installations, the details of which can only be accessed by an authorized Garmin dealer/installer. Cirrus pilots were reporting oscillations similar to what we're seeing and this SB addresses pitch performance. While it wouldn't be legal within the STC specifications to use this data for our Mooney installations it may be enlightening to know what fix Garmin put in place for the SR22. You can ask your installer if they'll take a look at it for you and share what's in it.

December 08, 2022 :  (2022) Service Bulletin 22113 Rev A: Approval of an updated maximum autopilot engagement speed and new gains for Cirrus SR22 aircraft

 

Cheers,
Rick