King KFC 225 autopilot

[M20R]

My KFC 225 autopilot is in need of repair. Can anyone recommend a repair station that works on the KFC 225 that is in or near north FLorida?

 

[KSMooniac]

You might call Bob Weber/WebAir consulting as a first step. He's active on beechtalk and helps a lot of folks with legacy systems.

Sent from my LM-V405 using Tapatalk

[carusoam]

Or have @Bob Weber find you….   (KFC 225 )

Best regards,

-a-

[LANCECASPER]

4 hours ago, M20R said:

My KFC 225 autopilot is in need of repair. Can anyone recommend a repair station that works on the KFC 225 that is in or near north FLorida?

 

A lot of people will dive right in there and start throwing parts at it by changing things out but they are not autopilot experts. They usually make things worse and harder to diagnose.  Talk to @Jake@BevanAviation OR @Bob Weber first. A lot can be done over the phone with the right person to steer you in the right direction. 

[carusoam]

M20R,

You might want to start the conversation with what you know is working and what you know isn’t behaving properly…
 

PP thoughts only,

-a-

[Jake@BevanAviation]

Best way to start troubleshooting the KFC225 system is to pull the error codes via the diagnostic port with a special cable and laptop.  Find a shop that has this ability and have them pull the codes.  In the flight line maintenance manual is all the error codes and the meaning.  That should isolate the issue down to a individual component.  Normally the problem is not the computer, it is some other component in the system.   

For repair you are going to be limited to Mid-Continent Instruments, Duncan Aviation and South-East Aerospace for bench repair.  Honeywell changed the dealer service agreement years ago and limited the service on KAP140 and the KFC 225.  You might reach out to Paul at Bragg Avionics in Jacksonville , they might have the capabilities to pull the error codes.

Edited April 29, 2022 by Jake@BevanAviation

[M20R]

I connected my laptop to the KFC computer and it showed "No error codes stored." I then went through and checked all the values and switches which we all ok.

When in flight in only the Flight Director mode, every thing works fine. It will show altitude and heading/nav perfectly. But when you turn on the AP mode the aircraft after several minutes start a climb followed by the electric trim operating in the opposite direction which results in a nose down and so begins a roller coaster ride.

[Jake@BevanAviation]

@M20R What was the value of the trim sense in the analog inputs screen?  It is not uncommon for the strain gauge in the pitch servo to get covered in dirt, grim, and get stuck causing the aircraft to auto trim more than needed.  Are you getting any audible messages of check pitch trim? Also, in the analog outputs screen you can command the servos to run to see if you have a servo drive issue.

[FlyingScot]

15 hours ago, M20R said:

My KFC 225 autopilot is in need of repair. Can anyone recommend a repair station that works on the KFC 225 that is in or near north FLorida?

 

I just pulled (last month) a complete KFC 225 system out of my 2000 O2 when I upgraded to a GFC500. I have all three servos as well as the controller box + cable harnesses. etc. All were working perfectly when removed - let me know if you need parts. Best - Bob

 

[Fly Boomer]

21 minutes ago, Jake@BevanAviation said:

What was the value of the trim sense in the analog inputs screen?  It is not uncommon for the strain gauge in the pitch servo to get covered in dirt, grim, and get stuck causing the aircraft to auto trim more than needed.  Are you getting any audible messages of check pitch trim? Also, in the analog outputs screen you can command the servos to run to see if you have a servo drive issue.

This is PhD-level knowledge!

[LANCECASPER]

1 hour ago, M20R said:

I connected my laptop to the KFC computer and it showed "No error codes stored." I then went through and checked all the values and switches which we all ok.

When in flight in only the Flight Director mode, every thing works fine. It will show altitude and heading/nav perfectly. But when you turn on the AP mode the aircraft after several minutes start a climb followed by the electric trim operating in the opposite direction which results in a nose down and so begins a roller coaster ride.

Did you try alternate static and see if it makes a difference?

[thinwing]

this reminds me of an pitch servo fault (not the strain guage )of the position sensor provided by a small moter but wired as an rpm sensor....mid continent provided rebuilt 272 \274 servos rebuilt for about 1200..Im sur e its much higher...but last servo maintance /repair was to a roll servo...that ended up as a cold solder joint that executive autopilots did in house as a board level repair...300 bucks....I have been hearing reports of servo failures on brand new Garmins that were supposed to put and end to ap problems....so im keeping my kfc 225 for now...two servo repairs (1 occurred when i first bought the plane) in 10 years ...I have found it to be smoothest most reliable ap ive flown behind

[ilovecornfields]

7 hours ago, FlyingScot said:

I just pulled (last month) a complete KFC 225 system out of my 2000 O2 when I upgraded to a GFC500. I have all three servos as well as the controller box + cable harnesses. etc. All were working perfectly when removed - let me know if you need parts. Best - Bob

 

^^^^ This. Probably cheaper to buy Bob’s old autopilot than to spend a bunch of money trying to troubleshoot yours. The servos will eventually die on you so it doesn’t hurt to have a backup.

[rbp]

4 hours ago, ilovecornfields said:

^^^^ This. Probably cheaper to buy Bob’s old autopilot than to spend a bunch of money trying to troubleshoot yours. The servos will eventually die on you so it doesn’t hurt to have a backup.

Yep! Pm me 

[M20R]

Trim sense value: -036.

[LANCECASPER]

4 hours ago, M20R said:

Trim sense value: -036.

Good idea to ping Jake so he sees this @Jake@BevanAviation

[Jake@BevanAviation]

@M20R  I would have expected the value to be closer to a null.  Might be worth a look at the sensor inside the pitch servo.

[M20R]

After lots of investigation I managed to diagnose the problem. It was the trim servo. I was able to borrow a pitch and a trim servo. When I changed the pitch servo, no improvement. When I swapped out the trim servo then everything works. 

[carusoam]

Nice follow-up R!

What’s next? OH the trim servo?

Best regards,

-a-

[LANCECASPER]

1 hour ago, M20R said:

After lots of investigation I managed to diagnose the problem. It was the trim servo. I was able to borrow a pitch and a trim servo. When I changed the pitch servo, no improvement. When I swapped out the trim servo then everything works. 

Not sure whether to take that literally or not that you swapped this out yourself. If you did I'm assuming that you're well trained and certified. There are a lot of things that owners can do (preventive maintenance) and even a few things that hangar elves do, but autopilot servos, tensions, adjustments, etc are way beyond my pay grade.

[M20R]

All work was done in accordance with the Bendix/King KFC 225 INSTALLATION AND MAINTENCE MANUAL, AUTOMATIC FLIGHT CONTROL SYSTEM FOR MOONEY MODELS M20M, M20R AND M20S 

All work was done by fully certified personal with proper log book entries.

Edited May 10, 2022 by M20R