KAP140 Autopilot Pitch Fault

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Rick
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Re: KAP140 Autopilot Pitch Fault

Post by Rick »

Victor wrote:Happy to report that cleaning tensioner rod as instructed few posts ago fixed the pitch fault problem! Trim wheel turns much smoother and had 10 out of 10 no error A/P startups! Will report on effects of colder weather in about a week.
That's great news, Victor! I just returned in the DA40 I've been flying after fighting all week with this same AP problem again and again, so I'm happy to hear of a possible solution. This DA40 goes in for its annual next week, so I will make sure they know about and check this out. Thanks for the good suggestion, Trey!
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Re: KAP140 Autopilot Pitch Fault

Post by blsewardjr »

My KAP140 has stopped working. Basically, it gets to PFT 3 in the test then stops and lines appear on the right side (which I believe indicates a vertical issue) and the P (and R) illuminate. The baro and altitude alert still function, however. In addition the electric trim is not working. The KC140 flight computer and roll servos were replaced less than three years ago. I've read through all the KAP 140 discussions and based on them the answer appears to be to clean the tensioner component at the back of the elevator and if that doesn't work look at replacing the pitch trim servo and/or updating its firmware. Does this seem like a reasonable approach? Thanks
Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

Bernie: Funny (not) that you should mention it. My KAP 140 just recently started exhibiting similar behavior. Today I cleaned the trim tension bar. Before I cleaned it it took >35 pounds to move it! After cleaning, I set it to 5.5 pounds, and the trim was much smoother. But it still failed the PFT test. Next week I'll plug in my laptop and download the error codes, but I am not optimistic that it is anything that can be fixed without several AMUs of new parts. The entire system is 2001 vintage (except for the KC 140, which was replaced under warranty in 2003).

It would be nice to have a description of what each of the 12 or so PFT tests checks, but I cannot find any document that describes them. I have the KAP 140 Flightline Maintenance Manual and the KC 140 Maintenance Manual (online).

To add to the misery, my KG-102A gyro is becoming intermittent as well. At least that unit I can pull myself and send off to be overhauled...

Steve
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Re: KAP140 Autopilot Pitch Fault

Post by blsewardjr »

Steve - Sorry to hear that. Thanks for the information. My KG-102A gyro is also making a lot of noise, but so far still holding on. I'm supposed to meet with the avionics guy this week to discuss where we begin.
Bernie Seward, IR, AGI
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KCHO Charlottesville, VA
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Re: KAP140 Autopilot Pitch Fault

Post by Karl »

blsewardjr wrote:My KAP140 has stopped working. Basically, it gets to PFT 3 in the test then stops and lines appear on the right side (which I believe indicates a vertical issue) and the P (and R) illuminate. The baro and altitude alert still function, however. In addition the electric trim is not working. The KC140 flight computer and roll servos were replaced less than three years ago. I've read through all the KAP 140 discussions and based on them the answer appears to be to clean the tensioner component at the back of the elevator and if that doesn't work look at replacing the pitch trim servo and/or updating its firmware. Does this seem like a reasonable approach? Thanks
Usually the first and usually cheapest thing to check/change is the AP disconnect switch.
Hopefully I managed to attach fault diagnosis chart which should help.
Attachments
KAP Fault Diagnosis.pdf
(32.41 KiB) Downloaded 161 times
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Re: KAP140 Autopilot Pitch Fault

Post by blsewardjr »

Karl- Thanks, much! This will be a great help. Bernie
Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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Re: KAP140 Autopilot Pitch Fault

Post by wolfvoador »

Hello, yes, same problem here. When starting in cold weather, getting the red P, and no altitude on the KAP140. Once out of clouds, and the sun shines on the fuselage in flight, I reset it,and it starts working. Last week, in North Carolina, 40 deg.F, I was in a hangar and we blew the hairdryer on the servo, for 2-3 minutes, and the pitch started to work.... maybe a solution for me here in Caribbean where I never encounter the issue, only if occasionally flying north.
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Re: KAP140 Autopilot Pitch Fault

Post by creativewebz »

hookem80 wrote:The trim wheel in the DA40 can be a BIG for the KAP140 A/P. Run the manual trim all the way up and down several times. If it sticks and is not smooth then it will cause the A/P to have pitch faults.
The trim wheel has a tensioner component at the back of the elevator in the tail of the DA40, it is a metal rod inserted into a Teflon block. The setup gets dirty over time and can stick, causing the A/P to show pitch fault. Cleaning this is easy and cheap compared to the AP repair, which still won't fix the trim tensioner problem!

Can someone please describe the cleaning (what exactly is it that you are cleaning, what is getting "dunked up")? My trim wheel seems to be slipping (some times not all the time or even in the same position). sometimes i am moving the wheel and the trim is not moving but the wheel spins.
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

Grant: What people are describing as getting "gunked-up" is the elevator trim Friction Damper rod, under the horizontal stabilizer:
DSCN5004.jpg
In the photo above it is the 6" long shiny metal rod going through the split Teflon block. It is there so that if the elevator trim cable breaks or detaches, the trim tab won't flutter. In order to set the tension on it, it must be detached from the trim tab. I then use an electronic fish scale to measure the breakout force. I usually clean it every Annual, but since it looked clean, I didn't in January. When I measured it last week, the breakout pull was >35 pounds! (It should be set 3.4-6.7 pounds according to the AMM). After cleaning, I set mine to 5.5 pounds. The elevator trim wheel was much easier and smoother afterwards...

Steve
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Re: KAP140 Autopilot Pitch Fault

Post by Rich »

Grant, if you can move the trim wheel (independent of the A/P trim) and the trim tab doesn't move you've got a problem with your trim control linkage. A gunked-up damper rod alone makes the trim inordinately stiff.

(BTW, I looked up N414DS and the FAA shows it as the registered number for a Cessna 414 owned by someone in Clackamas, OR. - you might want to look into that.)
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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