M20k 231 - KFC 200 autopilot nasty behavior

[fatalflaw]

Hi all

The KFC 200 autopilot in my M20K has developed a very nasty habit. While in the cruise, once in a while it commands and maintains a very large and sudden up-trim. I now am on top of it but the first couple of times it happened I was in hard IMC, turbulence, and I wasn't quick enough to prevent the situation getting out of hand, 1000 ft off alt and the controller asking me if I needed assistance (not sure what he was going to offer to do except take my license away). Fortunately I was high and in a lonely place.

Anyway, this happened twice on a flight across the Mediterranean today with my family on board and it needs to get fixed.

Anyone had a similar experience?

Disengaging the autopilot, controlling the attitude and altitude by hand and re-engaging seems to fix the problem, until the next time it happens. It seems to happen more when there is a lot of turbulence, but it has happened in clear still air as well. It has happens straight and level and also in descent, not during climb so far fortunately. The 'alt' light remains lit and the ap remains engaged till I disengage it. Trying to correct the tendency by hand with ap engaged requires huge forces, and isn't a solution.

Ideally I would like to understand and fix the problem rather than rip out the entire system and replace it, so suggestions along those lines would be the most welcome.

Best wishes to all

Jim

[jlunseth]

I had the same problem with my KFC 200 in my 231. It happened in turbulence, and I once had a 600 foot excursion before I got on top of it.  I never had it happen spontaneously in level flight though.  I wish I could tell you what the fix was.  I took it to our local avionics shop and the problem was gone, they fixed it and as I recall it was not very expensive.  All I can add is that forcing the nose down against the AP is only a very short term solution.  The trim runs harder to overcome what it thinks is an attitude that is too nose down.  The best solution is to hit the Disconnect button (big red button on the right side of the yoke) and hand fly. 

 

A similar but related problem can occur if the AP couples to the glideslope prematurely from below the GS.  The plane then tries to pitch up to make the GS and you either need to add quite alot of power, or again, simply disconnect and hand fly.

[BorealOne]

These are complex systems. I'd take it to the shop and let them diagnose it. It's not like most of us have the training or the tools to do anything useful to an autopilot anyway.

As a mere pilot, however, I can say with certainty that you don't want to be flying hard IMC with an autopilot that no longer performs reliably.

[Jack Burson]

Had this issue in my first Mooney years ago. Wound up having to replace an electronic "board". May have been the "mother board"

Jack

N4035H

M20K

[Danb]

I had runaway trim problems in my 1988 J model once in Ifr almost stalled the plane before I pulled the breaker I first tried stupidly to push the yoke in and it went harder up. Mine was a Kap 150 .had to have the board and trim servo changed before it was fixed completely

[manu damaschin]

...you will have to call Straubing (as I guess you are from europe), most likely you will need to overhaul the AP. I am having this problem as well and I think they are very relaible in fixing the KFC200...

[carusoam]

Consider getting the colored pieces that fit on the AP circuit breakers... Easier to find when this challenge occurs.

Best regards,

-a-

[cliffy]

One thing to check on a KFC 200 is to check and clean all the electrical grounds around the system. Servos, boxes, any where there is a ground wire, its connection to the airframe needs to be removed, cleaned and reattached. Solves many issues.

[fatalflaw]

Thanks guys! I think the consensus is:

 

1. Clean all contacts between autopilot and connected components to ground/earth

2. If that doesn't fix it, contact Straubing in Frankfurt.

 

That's what I'll go for for now.

Thanks again!

[PTK]

How dos it behave on the preflight test on the ground? Does it auto trim on the ground?

It may be as simple as replacing the contact switches in the trim servo. They wear.

[CoachTom]

Sometimes, running the autopilot through full range of operations will get it to run through the normal static locations on the servos where it usually is operated.  While on the ground, set heading on teh control panel and engage autopilot, then full left deflection and let the servos track, then full right deflection. For the vertical operation, set your altitude hold while the A/P is engaged and then do the same thing as you did with the altimeter which will cycle the trim servo as well.  Up and down/ left and right a few times...

 

Good luck! 

[Piloto]

It maybe a connector problem like others said. Disconnect all the related A/P and attitude gyro connectors and clean the contacts with contact cleaner. Reconnect the connectors.

 

José

[davidsguerra]

it is likely a bearing failure in the king  Attitude indicator.  clean or overhaul the attitude indicator .  i had the same problem and it was finally diagnosed after 3 trips to triumph avionics after being serviced 6 mos prior

[flyboy0681]

Consider getting the colored pieces that fit on the AP circuit breakers... Easier to find when this challenge occurs.

Best regards,

-a-

 

Which is the first thing I did when I had runaway trim problems.

[aviatoreb]

Which is the first thing I did when I had runaway trim problems.

 

My AP breaker cover is red.

[carusoam]

When I first saw these covers installed. I had mis guided thoughts...

Why would anyone want or need them?

Wouldn't it be obvious which breaker popped?

Then I realized...

When the AP is doing it's best to throw you for a loop, or into a loop in a misguided way...

It may be best to remove it's power to do so. It may take removing its power supply.

There are so many circuits in a modern mooney... Time may not be on your side.

So for you guys adding this thin layer of safety... I say (in modern mooney parlance) Bravo!

Best regards,

-a-

FB, thanks for supplying the documentary photo to support the discussion!

[bonal]

Not sure about the different systems I'm curious can the pitch control be deactivated while maintaining heading or NAV control. My Stek is only one axis. If you could turn off pitch you could at least trim out manually until problem fixed.

[DonMuncy]

I think we need to have a long thread on whether red or yellow is the preferred color for the circuit breaker marker.

[DAVIDWH]

My vote is for yellow,  for as any state trooper knows, yellow is a sign of unpredictability.

 

To this day I give yellow cars a wide berth.

[aviatoreb]

I think we need to have a long thread on whether red or yellow is the preferred color for the circuit breaker marker.

 

Life in black and white - or red and yellow:  Red is better.  It is obviously significantly much safer to mark your AP breaker with red than yellow.  In fact an airplane with a yellow plastic cover over the AP breaker should be considered unairworthy and grounded.  I would never fly even as a passenger in an airplane with a yellow breaker.