Electric trim intermittent failures

[ReconMax]

My 1998 J loses the electric trim almost every flight at some point. It causes the AP to kick off. We replaced the trim servo hoping that would resolve the issue but it persists. 
When it fails, it stays failed for the rest of the flight. 
There is no tripped breaker. Fiddling with the electric trim rocker switch does not help.

After shutdown, and turning master and radio switch back on does not fix it.

If I walk away and call the mechanic to look at it, its always working for him when he gets to it the next day.

When i return to fly again, its working again until sometime during the flight.

What could it be? I don’t think its the yoke switch because if it were the yoke switch the AP would probably keep working.

Any help would be appreciated. It stopped working and kicked off the AP just as i entered IMC. Took me a few seconds to realize what was happening. 
 

 

[carusoam]

13 minutes ago, ReconMax said:

My 1998 J loses the electric trim almost every flight at some point. It causes the AP to kick off. We replaced the trim servo hoping that would resolve the issue but it persists. 
When it fails, it stays failed for the rest of the flight. 
There is no tripped breaker. Fiddling with the electric trim rocker switch does not help.

After shutdown, and turning master and radio switch back on does not fix it.

If I walk away and call the mechanic to look at it, its always working for him when he gets to it the next day.

When i return to fly again, its working again until sometime during the flight.

What could it be? I don’t think its the yoke switch because if it were the yoke switch the AP would probably keep working.

Any help would be appreciated. It stopped working and kicked off the AP just as i entered IMC. Took me a few seconds to realize what was happening. 
 

 

I would invite @Jake@BevanAviation, but before I do… Let’s leave a note of what AP we are discussing… is it a BK KAP150?

 

If it is electric trim, independent of the AP…

Know that these things are susceptible to old grease issues…

Clean off the old… replace with new.  Should be butter smooth….

For real old grease… open the gearbox properly… clean and replace.  Gearboxes add challenge because they have certain spacers to contend with…

PP thoughts only, not a mechanic…

Best regards,

-a-

 

[N201MKTurbo]

What kind of electric trim is it?

[PT20J]

Trim is usually part of the autopilot. Which autopilot do you have?

[ReconMax]

2 hours ago, PT20J said:

Trim is usually part of the autopilot. Which autopilot do you have?

The autopilot is a KFC150 and interfaces to the G600 with the GAD64E. Im not sure about what kind of electric trim it is. 
 

We had the servo fail 18 months ago. I bought and installed a used one while i sent my original off to be rebuilt. After the unit was returned, we decided there was no need to put it in since the used one was functioning fine. But now 18 months later, with the constant failures that just started recently, we put the rebuilt unit in hoping it would solve the problem but it didn’t.

Thanks everyone for helping me think about it.

 

[PT20J]

@Jake@BevanAviation is the King autopilot expert here. Perhaps he can help.

[mooney_flyer]

Hi,
I’ve heard of cases where the wrong grease was used. The grease freezed.

That would explain your behaviour very well.

Good luck!


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[Jake@BevanAviation]

KFC 150 system has a trim monitor circuit that looks at the regulated trim voltage.  If for some reason the regulated trim voltage is dropping out or the trim servo is loosing power/ground the regulator will stop functioning.  When this happens the system will not pass pft and have a constant flashing trim light.  If you could get a video of the failure that might help a little.  Weak return springs in the MET (manual electric trim) switch have been known to cause intermittent issues especially the left side of the split rocker.

[ReconMax]

7 hours ago, Jake@BevanAviation said:

KFC 150 system has a trim monitor circuit that looks at the regulated trim voltage.  If for some reason the regulated trim voltage is dropping out or the trim servo is loosing power/ground the regulator will stop functioning.  When this happens the system will not pass pft and have a constant flashing trim light.  If you could get a video of the failure that might help a little.  Weak return springs in the MET (manual electric trim) switch have been known to cause intermittent issues especially the left side of the split rocker.

What trim light is flashing? Where? What would I video?

thanks

[PT20J]

[ReconMax]

Doh! Yeah. Okay. When the elec trim fails the AP kicks off. So no light then. But after, turning the AP back on, and selecting the Test, the Trim light does indeed flash constantly. 
 

I will get a video on Monday when i am going to be returning from our weekend trip.

Thanks for the help.

[Jake@BevanAviation]

Record the state of the failure, any flashing lights, what part of the system is INOP.  There is a trim fail light in the bezel of the flight computer.  During PFT test the trim light will flash 4 times.  If the regulated trim voltage is missing you will not get any flashes during PFT and it will have constant flash at the end of the test.  KC192 manufactured from 1991-1998 have issues with capacitor leakage and can cause some weird intermittent issues.   They tend to fail when they are thermal cycled, they will work when cold but tend to fail when the unit has been running.

m20 j kfc 150 interconnect.pdf

[ReconMax]

Okay, first, thanks everyone for the help. 

So yesterday we were prepping to depart Springdale, AR. My wife was videoing the electric trim issue. However, there was really nothing to see. It behaved exactly the way it was supposed to. I switched on the Master Power, then the Master Radio, then the Electric Trim Rocker Switch on the panel. When I engaged the rocker switches on the yoke, it moved fine. When I pressed the Test button on the KFC150, the Trim light blinked 4 times. 

Video Link

Since we were passing right by Don Maxwell, we decided to stop and talk to them. While on approach to GGG the electric trim failed again. After discussing it with Don, he decided the problem must be a faulty AP disconnect switch. We got in the plane, I showed him the electric trim wasn't working. Then, after fiddling with the AP disconnect switch, we got it to work, clearly implicating the switch. He had one of his guys replace it right then and there.

I feel confident that was the issue and everything worked fine for the next two legs of our flight. 

So, the switch was apparently breaking electrical contact potentially due to movement from turbulence or me bumping the yoke. They disassembled the old switch and burn marks were clearly visible inside.

I also got to see this cool experimental Mooney "Predator" built for the Air Force by Mooney. It has a canopy and a stick rather than a yoke and is fully aerobatic. So, the stop really worked out for me.

 

 

 

[carusoam]

Great follow up! ReconMax.

Fantastic pirep for DMax and co.

Great pics of the Predator!

I think the wing may have been swapped for a more docile, less aerobatic wing…. Standard Mooney issue…  (?)

Best regards,

-a-

 

[ReconMax]

Also, one more thing. I was advised by the Maxwells to stop using the big red AP disconnect switch to disengage my AP. They said use the trim switch or the button on the KFC150 instead. It's hard to stop but I'm slowly getting it done. A quick touch of the trim switch does it. It sounds like the failure of that switch is a thing they see commonly. 

I don't know how long my plane had that switch or if it was ever replaced in the past. 

I wish I could repurpose it to fire missiles.

[Fly Boomer]

4 hours ago, ReconMax said:

Also, one more thing. I was advised by the Maxwells to stop using the big red AP disconnect switch to disengage my AP. They said use the trim switch or the button on the KFC150 instead. It's hard to stop but I'm slowly getting it done. A quick touch of the trim switch does it. It sounds like the failure of that switch is a thing they see commonly. 

I think I read somewhere that it's kind of a wimpy switch for the task at hand.  I also recall reading that they are fairly cheap to buy {not from Mooney}.

[0TreeLemur]

On 4/18/2023 at 3:04 PM, ReconMax said:

I wish I could repurpose it to fire missiles.

I'd suggest that you turn it into an "EASY" button.

[Alan Maurer]

Hi...Flying Mooney Ovation with G1000 avionics and AP, my electric trim has quit several times. If I fiddle with the manual control wheel between the seats I can

usually get it working again. Sarasota Avionics got into the back and lubricated the gears or whatever and found nothing to repair but it still happens. 

So far it always starts working again! Annual soon...sure we will check all the possibilities again.

Cheers

Alan

[ReconMax]

On 4/27/2023 at 10:17 AM, 0TreeLemur said:

I'd suggest that you turn it into an "EASY" button.

What is an "EASY" button?

[Frank]

I have a similar issue in my Ovation. Of course it always works perfectly in the shop. It's probably the same disconnect button as the J, maybe I'll just replace that and see if the issue goes away. 

[ReconMax]

Let us know if that fixes your issue.