KAP140 HDG mode issue

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arksat
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KAP140 HDG mode issue

Post by arksat »

Last weekend I was flying from San Francisco Bay Area to San Diego and noticed that KAP140 autopilot's HDG mode flies 10 degree left from the heading bug in G1000 PFD.

Let's say I am in HDG mode, then I dialed the heading bug to 330, and the autopilot flies 320. Dial to 185 and fly 175. So there's always negative 10 degree gap, which is quite annoying.

Has anyone had this issue? I searched the forum but couldn't find relevant discussion threads.
My plane is 2005 DA40 (G1000 + KAP140).

I checked AHRS heading on my iPad (AHRS data from GTX345R) and it matches to the heading shown in G1000. So I guess KAP140 is doing something wrong... I had several flights in these days and had the same issues. NAV mode works fine.
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Steve
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Re: KAP140 HDG mode issue

Post by Steve »

There is an installation menu on the KFC140 which you can access from a laptop using a cable which plugs into the service jack. Both the course and heading datum offset can be adjusted to zero out the deviation. It is covered in detail in the Bendix/King KAP140 Flightline Maintenance Manual (available as a pdf on line). There may also be offset adjustments possible in the G1000 menus, but having a steam-gauge aircraft, I am woefully ignorant about the G1000...

Not sure why yours started doing this now, as the offset is usually set once, and unless you changed a box, shouldn't change over time. An avionics shop familiar with B/K autopilots should be able to help you if you don't wish to be an amateur avionics tech.

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Colin
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Re: KAP140 HDG mode issue

Post by Colin »

I had that happen to me. It was flying seven degrees right of heading, which was super annoying for a twenty hour flight from KHTO to KSMO. It took four visits to the avionics shop to fix it (along the way they replaced the gyro hidden behind the PFD). The field tech for King finally did the proper procedure to zero the datum.
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Kurt h
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Re: KAP140 HDG mode issue

Post by Kurt h »

I experienced the same problem on my G1000/KAP140. I don't recall the details but the avionics shop said the fix was within the KAP140, not G1000. The shop did mention the cable connection to a laptop that Steve mentions above. The first shop I called did not have this equipment so you may want to ask about their capability before you take it in.
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Rick
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Re: KAP140 HDG mode issue

Post by Rick »

I'm not aware of any adjustment within the G1000 either for this, but there definitely IS a heading offset value in the KAP140 maintenance menu. I would (have your avionics tech) start there. Not sure why it would have changed on its own though.
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Re: KAP140 HDG mode issue

Post by arksat »

Thanks for the info!! When I installed GTX345R I also asked avionics tech to turn down the volume of autopilot disconnect alert from KAP140 (the beep was piercing) so he has the cable and laptop.

We only changed the volume settings and didn't touch anything else, and the autopilot has been working fine after that. So I am not sure why this issue started just recently... :scratch:

Anyway I will need to visit avionics shop to re-calibrate GTX345R AHRS, so I will ask him to check the datum.
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Re: KAP140 HDG mode issue

Post by arksat »

Update- the issue has been fixed.

Went to avionics shop. Initially we tried to nullify the datum offset in config page, but we didn't see any changes. The mechanic called Bendix/King to find that null adjustment can be done by rotating the pot (accessible from front panel) in ROL (not HDG) mode. My autopilot was veering to the left even when the airplane is level on the ground with ROL mode selected, which should not happen. Rotating the pot until the veering stops nullified the offset in HDG mode too.
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Re: KAP140 HDG mode issue

Post by Nick H »

I just started having similar issue with my KAP140 (also in 2005 DA40 / G1000).
The info on the thread is very helpful. Question: how do I "rotate the pot (accessible from front panel) in ROL (not HDG) mode..."?
What does "pot" stand for?
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Re: KAP140 HDG mode issue

Post by arksat »

Nick-

"pot" stands for potentiometer. There's a small access hole above UP/DOWN key on KAP140 front panel. (not the one between NAV and APR button)
My mechanic used a small driver to carefully rotate the pot. Sorry I don't remember the screw's size.
If in doubt, let your mechanic call Bendix/King.
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Re: KAP140 HDG mode issue

Post by Rich »

As part of testing the recent Aspen installation I noted that my KAP140 still exhibits the right-of-course behavior when in HDG mode, with GPSS from the Aspen. This is the same behavior I saw with the original HSI. Behold, from the Aspen Installation guide in "troubleshooting":
Screen Shot 2021-03-20 at 11.23.19.jpg
But using this procedure requires removing the back seat to get at the connector and adjust the pot while the plane is stationary with the AP in ROL mode. :tap: So, thinks I, what if I just put it in ROL mode and guess at an adjustment, fly the plane and see what happens. So I did this and eureka! it works. I guessed at a bit of a turn CCW (~1/4 turn and it hit the stop.). The offset is still there, but it's less than the width of the lubber line. The KAP 140 process allows getting past the limit to get more adjustment, so I'll give it an extra bit of turn which ought to do it.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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