KAP-140 tracking error

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ahmebane
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KAP-140 tracking error

Post by ahmebane »

My somewhat-recently-purchased aircraft has the 525A HSI, 530W/430W, and KAP-140. Pretty standard 2003 plane (except for the WAAS).

I notice that when the GPS output is set to GPS, the autopilot tracks to a waypoint 100% as expected. CDI is centered.

When I'm tuned to either a localizer or a VOR, the autopilot steers the plane right of course - the CDI is about 1 dot to the left and stays that way. In addition, if the HDG mode is selected on the AP, the AP again steers the plane right of course; e.g., if I want to fly a heading of 180, I have to set the heading bug to 170.

Any theories as to what would cause this behavior? I'm going to have the shop fix it in my annual coming up, but I'd like to have an understanding of the issue before I turn it over to them.

TIA.
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Rich
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Re: KAP-140 tracking error

Post by Rich »

My ‘02 has had the same behavior. The heading deal can be alleviated by a qualified shop. The problem with localizer/RNAV, probably. I’m in the process of replacing my HSI with an Aspen so won’t be able to comment directly.
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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Rick
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Re: KAP-140 tracking error

Post by Rick »

I believe there is an adjustment for this in the KAP140 to center the LOC signal. I remember doing this in my first DA40 many years ago. You need a laptop and a special cable - your avionics shop should be able to do this.
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Rich
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Re: KAP-140 tracking error

Post by Rich »

Years ago I had the heading bug problem resolved by an instrument shop. It was the 525 HSI not sending a signal to the AP consistent with the mechanically-linked bug on the face. They told me it was a common thing to have to remedy. Also on the service report was a notation that they found several screws loose inside.

Current problem behavior is somewhat analogous: Example: Flying a coupled LP+V into my home airport in CAVU conditions, the AP was happily flying the proper bearing but off to the right and the CDI was correctly displaying that the proper course was parallel one dot to the left. Flying enroute does not exhibit any problems.

So is it the HSI or the AP? Good question. I would say a trip to an experienced shop is in order.
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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Davestation
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Re: KAP-140 tracking error

Post by Davestation »

There is a simple calibration setting for the heading, IIRC you just tell them how many degrees it is consistently off and they trim for it. Weird that it would randomly go out of calibration but it happens.
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