KAP140 Autopilot problems

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Matt Todd

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Matt T
I have a 2003 Cessna T182T (non-G1000) that has a KAP140 AP.

The ongoing problem I have is that after a period (time varies) in flight using the AP the aircraft will start to drift left of course regardless of whether it is in HDG or NAV mode. It won't respond to the HDG bug. I have to disengage and then re-engage the AP to get it to respond.

There are never any errors logged, no find anything when we test it.

I had the HSI checked, then we swapped it out and eventually replaced it with a Garmin GI275.
We swapped out the TC, still a problem.

On that back of that, we figured the problem must be in the AP computer, so we got an exchange unit. Still a problem!!

So 12 months and many thousands of dollars later I still don't have an AP I can rely on.

Has anyone else had a similar problem and/or any idea how to fix it?

Regards

Matt
 
Have you talked to Autopilots Central in Tulsa?
 
Thanks, I am based in New Zealand and have been working with one of the local but reputable avionics shops here, but we just seem to have hit a wall in terms of diagnosing the fault.
TrueCourse said:
Have the servos been checked?
Click to expand...
 
Thanks.
We replaced the pitch servo a few months ago, but we haven't looked at the roll servo. What would we test for to try and diagnose a fault.
 
Hi Matt,

Interested to know if roll servo maintenance was required and if it resolved the problem. I'm seeing the exact same problem recently in my 2003 182T.

Thanks,

Jason
 
Hi Jason,

They did check the roll-servo and in particular the clutch, but couldn't fin anything wrong with it.
Most recently the GI275 faulted (heading) and so it went back to the shop. They fixed the GI275 and reset all the nulls, My friend Rayden flew it home (just over 1 hour) and said there were no AP problems. I need to get a few flights logged before I would be comfortable to say we have resolved the fault. I am trying to do final consolidation for my instrument flight test which has made these problems doubly annoying.
So far we have swapped out the AI and TC, the refitted originals (as the fault was still present). Replaced the pitch servo (seperate fault). Swapped out the HSI then replaced it with the GI275, checked the roll servo. Redone the nulls on almost every occasion.

Hopefully it is sorted, but if I knew then what I know now I would have thought very seriously about replacing the KAP140 with Garmin GFC500.

Regards

Matt
 
Hi Matt,

Curious to see if the issue was resolved and what the fix was.. Having a similar issue with a 182T.
 
Hi, I fly a nice 182T G1000 bedeviled with KAP 140 autopilot problems. The latest maintenance attempt was to swap the "autopilot controller" with to no avail. Not sure what that is exactly. What about just throwing out the KAP 140 and buying another used unit? Or is the problem in the G1000 in how it talks to the King? Based near Toronto, Canada, suggestions welcome!!
 
Call Bob Weber autopilot consultant in Michigan.
 
Matt Todd said:
I have a 2003 Cessna T182T (non-G1000) that has a KAP140 AP.

The ongoing problem I have is that after a period (time varies) in flight using the AP the aircraft will start to drift left of course regardless of whether it is in HDG or NAV mode. It won't respond to the HDG bug. I have to disengage and then re-engage the AP to get it to respond.

There are never any errors logged, no find anything when we test it.

I had the HSI checked, then we swapped it out and eventually replaced it with a Garmin GI275.
We swapped out the TC, still a problem.

On that back of that, we figured the problem must be in the AP computer, so we got an exchange unit. Still a problem!!

So 12 months and many thousands of dollars later I still don't have an AP I can rely on.

Has anyone else had a similar problem and/or any idea how to fix it?

Regards

Matt
Click to expand...
When you swapped out the TC, was it for a new or overhauled unit? though it's been a decade, I know that my KAP140 needed to have correct turn rate information. When the TC got slow it would waver about the course line unreliably. Replacing the TC with a brand new one, each time after about 1000 hours of use, fixed it.

Since you don't sound like you are wavering about a mean course line, but rather are stuck on one side, the HSI bit is interesting. I know that I once had to have my KX55 aligned so that the course it was spitting out was in fact the one shown on the face. Sort of like trimming it. Was this checked when it was checked? I assume there's something similar for the 275 but don't know as it seems all electronic and "auto-calibrating."

The fact that it takes some time to fail course tracking could be related to heat as circuits warm up. Maybe something in the roll servo PCB is acting up. (Doesn't sound like it's in the computer itself since swapping did not change the event). In theory the servos are to be overhauled around 1000 hours but never had issues with any of mine (-271 and -270 I think). But if they have way more than 1000 hours, something to look at.

There was a wing walk issue a long time ago that was fixed with updated rate (gain) files, but this does not sound like it's your issue. Cable tensions are of course important to check with any autopilot.

Bob Weber is a good resource. If you are near to CA there's a very good shop in NorCal can recommend. And of course the GFC500 is AML'd for the restart 182s... At least the steam gage ones. Don't know about G1000 which is a more "closed" system since it's on the TCDS I believe.
 
A neighbor hanger club has a working when removed KAP 140 system available for sale. It was factory installed in a Cessna 182T, so should work for spare parts. If you are interested, contact me at n7083n@att.net.
 
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