Kap140 trim fail and other AP anomolies

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Cschobel
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Re: Kap140 trim fail and other AP anomolies

Post by Cschobel »

I have a 2005. I have replaced both servos. My A&P avionics guy 7 or 8 years is good for. Servo. I got a lot more then that.
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Diamond_Dan
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Re: Kap140 trim fail and other AP anomolies

Post by Diamond_Dan »

michael.g.miller wrote: Sat Nov 06, 2021 4:26 am
Colin wrote: Mon Aug 17, 2015 6:39 pm I would bet that is it a bad trim servo. I replaced two so far in 1,600 hours. Maybe it's been three.
What was the process to replace the servo? Did you replace entirely or try to overhaul? Was it expensive?
If you are anywhere near KHYA I highly recommend working with Bob Griffin at Griffin Avionics. He is the New England Sensei of the KAP. I just got my 2004 back from him today and he did a phenomenal job. My A/P probably had never been serviced so I had him check everything while it was in his shop: clean, bench test, re-calibrate the whole system. Had all needed parts in stock and updated the firmware too. Very happy with the rates, and no wasted time while troubleshooting.
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briankelly327
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Re: Kap140 trim fail and other AP anomolies

Post by briankelly327 »

My kap140 has failed multiple times on me over years. Pitch servo replaced. New computer (read refurbished old one). Only things I haven’t replaced are the roll servo which was replaced before I bought in 2016, and gyro.

Today the autopilot worked for the first 40 minutes of my 6.5hr flight to Florida and then veered the plane off course without correcting, far past a standard rate turn. Reset autopilot and it worked briefly, and then did it again. Waited. Recycled avionics completely. The kap ran its internal startup checklist ok. Tried again, this time it took me for a climb I didn’t initiate. Waited. Tried one more time and this time it worked for an hour or so, before it conked out again for the rest of the flight. One of these turns I allowed for a bit to see what it would do and I’m convinced it would have take me inverted. Pushing the pause button on the flight control and correcting course didn’t help. It almost felt like the autopilot servos turned on and then went static and didn’t adjust.

So - heads up for any pilots. This is dangerous if you’re not aware and in IMC. There were no red faults. No errors. When I recycled avionics the kap started up fine with no warnings, and then took me for a drunken ride.

If anyone has suggestions, I’m all ears.
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Steve
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Re: Kap140 trim fail and other AP anomolies

Post by Steve »

Brian:

The KAP140 stores an error log internally (some of these do not annunciate as errors). You can download this log (plus do a lot of additional troubleshooting) by connecting your laptop, as a serial terminal, to the port under the instrument panel using a special cable (which you can make for a few dollars worth of components). I have used it a couple of times to diagnose issues which allowed ridiculously inexpensive repairs without going to an avionics shop.

Shortly after I got the airplane, I did have an intermittent, recurrent issue similar to yours, except that the excursions were vertical (sudden uncommanded 700 fpm dive). That was corrected by a new computer. All of my servos are original, and continue to work well after 20 years.

There, now I've jinxed myself...
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