KAP140 Autopilot Pitch Fault

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Rick
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KAP140 Autopilot Pitch Fault

Post by Rick »

We are having some issues with the KAP140. A least half the time, it works fine. But sometimes after a powerup, it will complete its selftest ok, but display the red "P" symbol - denoting a "pitch fault". When it is in this state, the ALT mode will not arm or engage, and the altitude knobs have no affect. Cycling the AP circuit breaker produces the same result after the next selftest. I have flown trips in this state - NAV works fine, just no altitude hold. Next trip, maybe no problems at all, or maybe the same problem.

Dumping the error log file in the KAP140, I see the following message a number of times:

Error in Encoding Altimeter Input
The parallel altitude information from the altimeter is not a valid Gilham code. The altimeter may be powered off or there may be a broken wire in the harness. The Altitude ARM mode will be disconnected if this occurs.

I guess I am looking for somebody to help me understand where the KAP is getting its altitude information from. There is a red static-type tube connected to the back of the KAP140 - not tied into either the blue or green pitot-static lines, but I can't tell where it goes. Apparently there is some sort of pressure sensor somewhere for altitude, and then maybe also some altitude signal from the G1000? The error message seems to indicate the G1000 connection may be bad (or intermittent)?

Has anyone ever had a problem like this before?
2007 DA40 XL - Roanoke, VA (KROA)
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Victor
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Re: KAP140 Autopilot Pitch Fault

Post by Victor »

Rick,
I have the same problem. After doing some research and some trial and error I concluded that servos are very temperature sensitive and error out on startup if they are below 50F. (for some reason only pitch servo errors out). KAP140 has its own altitude encoder so if you see that error, the setting for external input must be set to on.
v
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Charles K
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Re: KAP140 Autopilot Pitch Fault

Post by Charles K »

How did you get an error log from the KAP 140 ???
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Re: KAP140 Autopilot Pitch Fault

Post by Rick »

Victor wrote:Rick,
I have the same problem. After doing some research and some trial and error I concluded that servos are very temperature sensitive and error out on startup if they are below 50F. (for some reason only pitch servo errors out). KAP140 has its own altitude encoder so if you see that error, the setting for external input must be set to on.
Victor, interesting theory. I can't remember the temperatures corresponding to when it works or not, but I will check the MFD data logs and see if that makes sense. Did you ever find a solution for this problem?
Charles K wrote:How did you get an error log from the KAP 140 ???
Charles, you need to make up a special cable, and find a laptop with a serial port on it. PM me if you want more info. Or, any avionics shop that works on King products should be able to dump it.
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

My aircraft had recurring pitch trim failures when it was about 6 - 12 months old. Eventually, they replaced the computer with a refurbished one. Same problem reappeared about 3 months later! This time they replaced it with a new computer - no problems since then, 8 years, knock on wood.

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Re: KAP140 Autopilot Pitch Fault

Post by Tim H »

I had this occur one time on my DA40. It was cold (5 F) at altitude. I hope this is not a temperature related issue because I don't think 5 F at altitude is all that cold. Should be a more robust design.
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Re: KAP140 Autopilot Pitch Fault

Post by Rick »

Steve wrote:My aircraft had recurring pitch trim failures when it was about 6 - 12 months old. Eventually, they replaced the computer with a refurbished one. Same problem reappeared about 3 months later! This time they replaced it with a new computer - no problems since then, 8 years, knock on wood.
Steve, when you say they replaced "the computer", what exactly do you mean - the KAP140 unit itself?
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Re: KAP140 Autopilot Pitch Fault

Post by Victor »

Charles,
To get logs and for other diags you'll need to get cable from BK. Or you can make one out of serial cable and U-174/U Connector. If you need pinouts PM me. Then I used Serial-to-USB converter and regular terminal program set to 9600-N-8-1.

Rick,
So far no solution. I have read that some folks replaced the whole servo for $1800 plus labor. Also seen some mention of use of different grease, but not sure that would help.
Today I confirmed my hypothesis, in the morning after 45F night pitch refused to initialize failing at step 3. flying back in the afternoon with warm cabin, everything worked like a swiss watch.
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Re: KAP140 Autopilot Pitch Fault

Post by Rick »

Victor wrote:Today I confirmed my hypothesis, in the morning after 45F night pitch refused to initialize failing at step 3.
I will check again, but I don't think my AP selftest fails at step 3 - I think it completes succesfully, even when I have this failure. Now that it's warmer, though, maybe I won't see it again for a while... I'll have to pay closer attention!
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Re: KAP140 Autopilot Pitch Fault

Post by Charles K »

Victor - yes I would appreciate the pinouts and command set used to read out the logs.

Thanks !
Victor wrote:Charles,
To get logs and for other diags you'll need to get cable from BK. Or you can make one out of serial cable and U-174/U Connector. If you need pinouts PM me. Then I used Serial-to-USB converter and regular terminal program set to 9600-N-8-1.

Rick,
So far no solution. I have read that some folks replaced the whole servo for $1800 plus labor. Also seen some mention of use of different grease, but not sure that would help.
Today I confirmed my hypothesis, in the morning after 45F night pitch refused to initialize failing at step 3. flying back in the afternoon with warm cabin, everything worked like a swiss watch.
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