KAP140 Autopilot Pitch Fault

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Bartek
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Re: KAP140 Autopilot Pitch Fault

Post by Bartek »

I think I am seeing something similar to that with mine KAP. Last few months it was becoming less and less reliable. First Heading Bug mode was out, latter NAV, eventually even ROL is dead most of the time (some six horizontal bars displayed on AP). Had it checked a week ago and neither KAP or HSI was found faulty. The avionic workshop suspects some loose connectors or some wiring issues, wanted airplane to stay for two days for more thorough inspection. Had no time that moment, we are scheduled again coming Monday, will let you know if they find something.
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Re: KAP140 Autopilot Pitch Fault

Post by Victor »

Performed the experiment with taking KAP140 out few times. No luck here, still 33 and red "p". hope Rick comes back with some results of his investigation.
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Re: KAP140 Autopilot Pitch Fault

Post by Tim »

I had a bunch of 'PT' annunciations on the KAP140 today during my six approaches for currency. 'Pitch Error' on the G1000 and even 'Pitch Trim' voiced annunciations with a helpful arrow on the unit to show which way to (manually) move the trim wheel. The trim control on the joystick did not appear to be working.
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Rick
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Re: KAP140 Autopilot Pitch Fault

Post by Rick »

Victor wrote:Performed the experiment with taking KAP140 out few times. No luck here, still 33 and red "p". hope Rick comes back with some results of his investigation.
I've kind of been waiting for something concrete to report! My problem went away when the weather warmed up. I do now believe it is temperature-related because I had one additional "P" fault on powerup one (rare) cold morning back in June, after the "re-seating" incident. I now think the re-seating seemed to "fix" the problem only because it also got much warmer about the same time. Not a single fault since that one back in June.

I guess we'll know for sure if the problem reappears this fall. :scratch:
Tim wrote:I had a bunch of 'PT' annunciations on the KAP140 today during my six approaches for currency. 'Pitch Error' on the G1000 and even 'Pitch Trim' voiced annunciations with a helpful arrow on the unit to show which way to (manually) move the trim wheel. The trim control on the joystick did not appear to be working.
If the red "PT" light was lit on the KC140 unit when this happened, then you should be able to pull the error log from the unit and find out what caused the error(s). The G1000 annunciations were probably just caused by the AP fault. First suspect is the Electric Trim switches on the joystick - one of them may have been stuck. Were you using your iPad at the time, Tim, maybe laying it on the trim switches? ;)

Do the trim switches work now? Were they working ok before this incident? If it happens again, try moving the trim switches back and forth a couple times to see if one of them was stuck.
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Re: KAP140 Autopilot Pitch Fault

Post by Tim »

I went back to the plane today, to do a couple of things including refueling. I played around with the electric trim and it does work via the joystick switch but it's quite noisy with a big click when I release the joystick switch that I don't remember hearing before. I was on the ground, so couldn't test with the AP but will this weekend. The trim wheel worked normally and smoothly by hand.
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Re: KAP140 Autopilot Pitch Fault

Post by hookem80 »

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!
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Re: KAP140 Autopilot Pitch Fault

Post by Tim »

Thanks. I will take a look at this during next maintenance. I have not had the AP pitch fault in the two flights since my post above. I did notice some gentle porpoising yesterday climbing to 15.5KFT, mainly above 10K. It happened both in the climb and a descent to 14.5K. I chose to disengage the AP and hand fly. In cruise, no porpoising at all. Perfect.
PS. some interesting data from the flight.

13,100 (DA 15,200) Fuel pressure low annunciation. Switched to electric fuel pump.

14,500 Freezing level

15,500 (DA 17,136) Top of climb. 30 minutes from 400 feet. . Average 500fpm.
118TAS, 91 IAS, 16.8", 2230rpm

14,500 (DA 16,000) Descent. AP caused porpoising.
117TAS, 90IAS, 17.5", 2220rpm, 6.1gph
As above but 2000rpm, 5.6gph, 112TAS, range = 730

As above but 2300rpm, 6.6gph, 125TAS, range = 604
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Rick
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Re: KAP140 Autopilot Pitch Fault

Post by Rick »

Well... the Pitch Fault problem, which had been absent all summer, returned over the weekend. Can't really say why, or pin it directly on temperature. When I left Friday morning, OAT was in the mid 70's - a bit cooler than it has been, but nothing like last spring when we were having this problem all the time. Could not get the AP past self-test #3 again, and no satisfying thunk of the servo kicking in like it normally does, so I'm leaning toward a servo problem now. But after probably 12-15 power resets, it finally passed the tests and then worked fine all trip. Go figure... :scratch:
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!
Good point, Trey. I had this problem with my previous DA40, and cleaning and resetting the tourque on the Teflon block fixed that problem!

With this current problem, I do not believe elevator trim is involved, though. In my case, the AP fails with a pitch fault maybe 5 -10 seconds after turning the avionics on - won't pass self-test #3. I'm thinking the other version of the pitch fault you are referring to (or is it a pitch trim fault?) only happens in flight, when the AP is trying to adjust the trim. It seems there are many ways to upset the KC140...
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Re: KAP140 Autopilot Pitch Fault

Post by Doug »

It appears to be the same issue that I had with the KAP 140 in my 42. The servo was fubar'd, it was also discovered that the servo was an old rev mod. Worked fine after OH'd unit was installed. Mine as was warranty so can't advise on amu's.
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Re: KAP140 Autopilot Pitch Fault

Post by Victor »

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.
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