KAP140 sudden turns

[LTek1]

In the 30 hours I've flown my plane since I got it, this has happened twice:

When flying along following the GPS as the NAV source, a get a sudden standard rate turn to the right. The first time it happened, I thought the AP had disconnected and realized it was still engaged when trying to turn us back onto course.

So, out of curiosity, the other day I let it go to see what it would do. I noted as soon as it hauled off to the right that we were a bit left of course, so I hoped it would intercept the NAV source and straighten out. But it powered past the course; I let it continue for 90 degrees before disconnecting and setting us back up in the right direction.

In both cases, the AP re-engaged and flew the rest of the flight with no issue.

Any ideas?

[carym]

I can't tell you why this happened except to say that it does. Last week I was flying thenGPS 18 approach and was on the final approach course when it decided to stop following the course and wanted to track left. Whenever on autopilot i always make sure I am ready to disconnect. I also have the autopilot circuit breaker marked so I can disconnect if needed in the dark.

Since the KAP140 is a rate based autopilot driven by a standard turn coordinator, it may be a signal that the turn coordinator is going out. I know of no way to check this out except at an avionics repair station.

[Rich]

Typically, a problem with the signal from the turn coordinator gives you a battle between a turn to the left and trying to get back on course.

Some years back I had a problem where the plane went bonkers as described here. It turned out to be a connector between the HSI and the FC had come loose at the HSI. It was quite obvious. There are a set of locking pins in the connector and one had come loose, with the result that the connector was partly engaged, at an angle. Fixing the locking pin (it had come unscrewed) and reconnecting cured the problem.

[nathanda40]

In the 30 hours I've flown my plane since I got it, this has happened twice:

When flying along following the GPS as the NAV source, a get a sudden standard rate turn to the right. The first time it happened, I thought the AP had disconnected and realized it was still engaged when trying to turn us back onto course.

So, out of curiosity, the other day I let it go to see what it would do. I noted as soon as it hauled off to the right that we were a bit left of course, so I hoped it would intercept the NAV source and straighten out. But it powered past the course; I let it continue for 90 degrees before disconnecting and setting us back up in the right direction.

In both cases, the AP re-engaged and flew the rest of the flight with no issue.

Any ideas?

I know I'm reviving an ancient thread here, but did you ever get it sorted out? Our 2002 DA40 is having this issue

[LTek1]

To be honest, I've flown so little in the last few years that I can't say definitively if anything has changed. I will say, I have not seen it do this in the few hours I have spent on the autopilot. We didn't do anything specifically to fix it, but we did replace the transponder a few years ago, which means the panel was apart. :shrug:

[Charles K]

Could also be the roll servo going bad. Thus far in my 2004 I have replaced one TC and one Roll Servo.

[nathanda40]

Could also be the roll servo going bad. Thus far in my 2004 I have replaced one TC and one Roll Servo.

What makes me think it's not one of the servos is that if you hit roll mode while it is making the un-commanded turn it stops and levels out.