M20K with KFC-200 Problems

[MooneyMuscle]

Hello Mooney Experts

My buddy has a M20K with the KFC-200 autopilot that feels like you are riding on waves when the Alt hold is on.  He thought it was so slow to response so at annual he had roll and pitch sent off for overhaul at mid continent.  Now this issue...Any Advice? Shop wants to sell him the GFC500 and G5s.... I doesn't want to get deeper into the plane. 

Thanks

Edited November 11, 2020 by MooneyMuscle

[spistora]

I've had pretty good luck talking to Jake at Bevan Aviation @Jake@BevanAviation with KFC200 issues in my M20K.

[PT20J]

Executive Autopilots and Mid-Continent are also good for consulting. I had this problem years ago and it turned out that water had intruded into the static lines and into the pressure transducer. I pulled the circuit board out of the computer and shook out all the water and it worked fine after that.

Skip

[jlunseth]

The first thing you should have him do is check under the trim wheel, between the wheel and the floor, for debris, like bits of food or the like. There is not much clearance there, sometimes things get under the wheel and affect the performance of the trim. After that, have the servos and chain lubricated. Then on to the avionics shop. Its a very good AP, I would not replace it unless it were truly toast.

[LANCECASPER]

Time to call @Bob Weber

https://webairconsulting.com/

[Jake@BevanAviation]

Having a better description of the issue might help narrow down where to start looking.  Some good questions to ask would be.

• What are the flight bars doing?
• Is the issue only related to alt hold?
• How large is the change from target altitude?
• Has the bridal cable tension been checked?
• Can the system hold a 5 deg climb or descent?
• If the static line is removed from the KC-295 is the issue still present?
• Has the attitude source (KI-256) been changed recently?

If your friend has a video of the issue that might help as well.  Just be sure to have the ADI and annunciator in the shot. Also, knowing what series of pitch servo would help.  Depending on the serial of the aircraft it could have the KS-270 or KS-177 pitch servo.  If your friend would like to chat about the issue they can always give me a call.

[tmo]

Allow me to throw in a few KFC200 questions in here instead of starting a separate thread.

How many times is the "trim" annunciator supposed to blink during the self test on a M20K KFC200? The AFMS says "four or more" - mine does five every time - good or bad? Also, is it supposed to beep at the end of the self test - AFMS says so, but mine never does; it does beep when the AP disconnects.

Last year My KFC200 worked like it was on rails, even if I skipped the pre-flight test and just engaged it in flight. This year it started pitching down when in altitude hold mode. Now, during the self-test on the ground, it not only pitches down, but also turns to the left. While the AFMS cautions that autotrim may run on the ground due to lack of aerodynamic forces on the elevator, it doesn't explain the left aileron. FD bars look "straight and level" to me.

Weather isn't allowing for any in-flight testing, so I'd like to solicit suggestions for when it does, as well as for tests that can be run on the ground, preferably without engine running - if anything can be tested that way.

[carusoam]

Thanks to Jake!

Great to have your input.

Best regards,

-a-

[Jake@BevanAviation]

@tmo What I could find in the flight line MM is that trim should flash 4 times for a successful test along with all mode annunciations illuminated.  Observations on the bench are.  With no modes selected, holding the TEST button will light all mode annunciations as long as the TEST switch is depressed and trim will flash 4 times for a successful test.  The computer will send a up trim command and then a down trim command for approximately 1 second for each direction.  Up is always first, there is a small delay then down.  When releasing the TEST button it will do the same test again as the caps are discharging on the adaptor card but, the time is drastically reduced. 

Attached is the POH for the KFC 200,  page 27 outlines a ground and PFT test with results you should see in the aircraft.  I could not find any mention of a beep as the system should be disengaged during the test.  Disconnecting the system should give a alert pending you have the updated control head.  A good rule of thumb is on the ground you should always test the system as much as possible.  Modes like G/S capture or NAV/APPR ARM might be difficult to test unless you really know the equipment in the aircraft.  However, the basic functions should always be checked like those mentioned in the POH.  Those ground checks should be a very quick and easy test.

For the ALT hold issue,  does the aircraft ever level out after the descent or is it just a slow constant descent?  There is a pot on the pitch card inside the KC-295 that might help with a alignment issue for alt hold but, it will not fix it if there is a constant descent with no level out.  Alt hold cards are known to fail from time to time but, when they do it's normally a constant up or down drive that is fairly aggressive and they will never level out.  A shop with the KTS 150 flight line test kit should be able to quickly tell you if it was a alt hold card issue.

KFC 200 POH.pdf

[jlunseth]

That is helpful Jake but my experience is that the test does not indicate the issue that the OP is talking about. The trim is making small changes in flight and then reacting back the other way, they are not very big changes, but it creates the "wave" feeling. 

[tmo]

@Jake@BevanAviation - thank you; both the Mooney AFMS and the POH you posted do say "four or more" flashes - so I am wondering if the fifth one is at all significant. FWIW, mine never moves the trim during the self-test; I will try to hold the button in longer - perhaps I am just too impatient. The Mooney AFMS (page 8) mentions an "audible warning" which the King publication does not, and which I am not getting. I'll go with "that's ok" for now. And hope for a chance to do an in-flight test at a safe altitude. Thanks in advance for any further troubleshooting suggestions.

@jlunseth - I hijacked the thread, apologies; my AP does a constant trim down, to the stops a short time after ALT mode is engaged; the OP's AP oscillates in ALT mode.

[MooneyMuscle]

Thank you for all the info, ill pass it on.

[jlunseth]

@tmo - for whatever reason, it seems to take forever for the trim to start to move when you do the self-test, but eventually it does move. It is not an immediate move as it is when the aircraft is flying.

[carusoam]

For comparison...
 

The newer (yet less capable) KAP 150 has audible beeps at the end of a successful test...

I once thought these beeps were meaningful to what step was successfully completed.... but it seems that I may have made that up... 

It is the same tone when the AP gets disconnected...

Best regards,

-a-

[tmo]

Thanks guys; the forecast for Sunday looks somewhat promising, will attempt some testing (including an extra long self-test to get the trim moving) and update here.

[bgpilot1]

I second the opinion to call Bob Weber at webairconsulting.com.  He really knows the analog autopilots and helped me fix a trim servo issue with my KAP150 that Duncan Avionics overhauled twice without fixing the issue.  He is really good at working with you or your avionics technician to isolate the issue and identify the proper fix.

[carusoam]

Great pirep for Bob Weber....  @Bob Weber

Thanks for sharing...

Best regards,

-a-