KAP 140 Check Pitch Trim

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GarthC182

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Jun 10, 2021
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GarthC182
My KAP140 Autopilot began annunciating "Check Pitch Trim" in mid-flight. Over the last 8 months we have serviced or exchanged the Flight Computer 3 times, serviced the Pitch servo, and ran multiple Hyper-Terminal diagnostic reports to no avail. I have been in multiple communications with Mid-Continental, and Ducey, and have been making the changes and providing the diagnostics at their direction, but they seem incapable of resolving the problem. Has anyone encountered this problem or know of a shop tech with experience at the firmware level with KAP 140's?
 
There are two servos in the pitch system of the KAP140 - Pitch servo and Pitch Trim servo. Did they check both of them? The other thing that can lead to Pitch trim faults is excessive friction in the (manual) pitch trim system. Can you run your pitch trim to the limits both ways without undue effort?
 
Even though the error says "check pitch trim" Mid-Con advises the problem is with the pitch servo and not the pitch trim servo. I had the pitch servo serviced by SouthEast Aerospace and they replaced the cantilever arm and strain gage and certified the servo. Upon re-installation the problem is now that the Autopilot computer will not complete its self check. Normally on startup the FCC would cycle through PFT 1 to PFT 9, lights all digits, and then go to normal operating mode. With the replaced pitch servo, the FCC gets to PFT 3, jumps to all digits light, and then to what looks like normal operation mode. However, there is no trim operation and "check pitch trim" then gets annunciated. Operating pitch trim manually to both limits is no problem and no additional load from past normal operation is detected. The baffling thought is why does it fail at PFT 3 which Mid Con does not seem to be able to answer. They think it is the FCC but we have received an exchange unit from them, and the same problem persists.
 
The other thing that can cause the computer to PT fail at PFT 3 is an open AP disconnect switch circuit (red button) - ask me how I know this :rolleyes:. You should be able to spot this with the diagnostic terminal plugged in, or if you want to try yourself, just short the switch (both of them, actually) with a clip lead jumper. If the autopilot completes the preflight test, you have found your problem.
 
The AP Disconnect appears to function properly. The diagnostic information displays correct function, and the limited function of the FCC after initial test failure allows the autopilot to engage (without pitch control or operation) and the AP Disconnect press then properly disconnects the autopilot.
 
That is a weird situation. You have already switched out a (presumably) known good FCC, and that didn't fix the problem. The last thing that was worked on was the Pitch servo, and the failure mode changed after this. I would check all of the wiring between the FCC and Pitch servo including the connectors, and if that checks out good, try to obtain a known good (new or BK rebuilt) Pitch servo.
 
Yes, we exchanged a FCC from Ducey when the "check pitch trim" happened with the same result, and then another FCC from Mid-Con to troubleshoot the PFT 3 failure, again with the same result. At least the problem replicates! Exchanging out the pitch servo is the point we are at now. What is missing is the technical explanation of the inputs that cause the FCC to generate the "check pitch trim" annunciation, and, more recently, what the software/firmware is checking when it then jumps out of its PFT 3 self-test? Do you know where technical knowledge at this level can be sourced?
 
There is a KAP 140 Field Maintenance Manual that has a lot of good info for troubleshooting. I found it somewhere on the internet for download as a .pdf some years ago. I could email you a copy if you send me your email address...
 
If you are referring to the Honeywell Flightline Maintenance Manual then I have a copy. Mine is Rev 2 Dec 2002. It makes reference to PFT's and "check pitch trim" messages but is not detailed enough to say how to then troubleshoot the problem. I also have wiring schematics and pin-outs for the connector harnesses which allow continuity checks, but again, without knowing the firmware I/O it could be any number of things. That is the level of technical expertise I am trying to find to say "this is the incorrect input that is causing that output". Without that expertise, we are left with exchanging this and that until the problem hopefully goes away. Expensive, time consuming, and not owner satisfactory; nor would I think for the vendor.
 
I am a new member here after finding this discussion about the KAP-140 “Check Pitch Trim” warning. I am having the same issue. Mine started immediately after disconnecting the A/P on approach. I had to pull the CB and continue the approach. My A/P is 20 years old, almost to the day.

On the ground, I ran some checks:
1) Power on self test completed without errors or lights for “P” or “T”.
2) I could here the Pitch Solenoid activate in the back of the plane during POST.
3) Almost 10 seconds after the POST completed, the aural warning started up again.
4) I can use the manual electric trim, both UP and DOWN.
5) Even though the A/P is not engaged, pressing the A/P disengage on the control wheel disables the audio warning for about 10 seconds.
6) I have access to a Flight Control Computer and swapped out with mine. Same aural warning after POST.
7) On the ground I tuned a VOR and engaged the A/P.
Adjusting the course the control wheel followed the required back to intercept.
The trim UP was engaged since the altitude selected was higher than the current altitude.

At this point I am out of trouble shooting options and no avionics shop in my region will touch the KAP-140 since B/K no longer supports it. I may have access to some servos removed from another 182. One thought was to just plug in the spare servo without mounting it or rigging it and run a test. Would this actually work or does the servo need a load?
 
NavAir,
Is it possible to get a copy of the KAP-140 Flightline Maintenance Manual you offered to send someone on your post dated June 15, 2021 above?
Thank you!
 
Here you go...
 

Attachments

  • KAP140FMM.pdf
    1 MB · Views: 32
NavAir,
Thank you Sir! I appreciate your help. Got a heading mode offset issue with my KAP-140 and this will help me resolve it.
Thanks again,
Garry
 
LARRY HINTON said:
I am a new member here after finding this discussion about the KAP-140 “Check Pitch Trim” warning. I am having the same issue. Mine started immediately after disconnecting the A/P on approach. I had to pull the CB and continue the approach. My A/P is 20 years old, almost to the day.

On the ground, I ran some checks:
1) Power on self test completed without errors or lights for “P” or “T”.
2) I could here the Pitch Solenoid activate in the back of the plane during POST.
3) Almost 10 seconds after the POST completed, the aural warning started up again.
4) I can use the manual electric trim, both UP and DOWN.
5) Even though the A/P is not engaged, pressing the A/P disengage on the control wheel disables the audio warning for about 10 seconds.
6) I have access to a Flight Control Computer and swapped out with mine. Same aural warning after POST.
7) On the ground I tuned a VOR and engaged the A/P.
Adjusting the course the control wheel followed the required back to intercept.
The trim UP was engaged since the altitude selected was higher than the current altitude.

At this point I am out of trouble shooting options and no avionics shop in my region will touch the KAP-140 since B/K no longer supports it. I may have access to some servos removed from another 182. One thought was to just plug in the spare servo without mounting it or rigging it and run a test. Would this actually work or does the servo need a load?
Click to expand...
 
Good day, I’m also new to the site. I’m have the same problem with the pitch trim in mid flight. What did you guy find with yours?
 
When was the last time the servo clutches were checked for correct friction?
 
I have not checked it yet , but sounds like a good place to start. Thanks
 
Has anyone on this thread found a solution to this “check pitch trim” issue?
 
This issue was resolved on my plane by swapping the pitch servo. The load sensor within the servo was sending a signal that indicated an constant out of trim condition. Regardless, have a good avionics shop troubleshoot the issue before spending money on a pitch servo exchange.
 
GarthC182 said:
My KAP140 Autopilot began annunciating "Check Pitch Trim" in mid-flight. Over the last 8 months we have serviced or exchanged the Flight Computer 3 times, serviced the Pitch servo, and ran multiple Hyper-Terminal diagnostic reports to no avail. I have been in multiple communications with Mid-Continental, and Ducey, and have been making the changes and providing the diagnostics at their direction, but they seem incapable of resolving the problem. Has anyone encountered this problem or know of a shop tech with experience at the firmware level with KAP 140's?
Click to expand...
I have experienced the exact same problem and unable to resolve in the past 9 months. We’re you able to resolve?
 
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