Kap140 trim fail and other AP anomolies

[Gearle]

So I now have a 2003 da40 Kap140 garmin non WAAS 530/430, 330. On cross country trips I have had trim failures, where I cancelled the AP (without pulling the circuit breaker) and reengaged it.

I read a few of the previous posting here, with some concerned about their actual AP and servos. I then ran across this article that reflects my experience so far, indicating it is the sensitiveness of the self testing and self monitoring of the KAP, and not necessarily mechanical failures of the AP system.

http://poweredbylycoming.blogspot.com/2 ... rt-of.html

Excerpts:
The KAP140 can be finicky...
Pitch trim fails during self test...
Doesn't like cold weather...

Including a good idea about autopilot driven porpoising (adding a second static port)...

So finicky maybe the design intent...

[Colin]

I would bet that is it a bad trim servo. I replaced two so far in 1,600 hours. Maybe it's been three.

[Tim H]

Something you might consider is adjusting the trim mechanism and making sure that it is serviced to the AMM limits / specs. I think there is a self-lubricating friction block in the tail near the trim tab. It should be clear of dirt and debris and not lubricated. I had similar issues and all it took was a good cleaning to fix the issue.

[BlackMammoth]

Definitely clean the friction block under the elevator.

This made a significant difference in trim effort (using wheel to gauge resistance) on our aircraft.

[BlackMammoth]

I replaced two so far in 1,600 hours. Maybe it's been three.

Ouch! We are still on the original servo with almost 1800 hrs. The autopilot is used on just about every flight, for the majority of the flight.

Anyone else experience autopilot servo failures?

[Cschobel]

I had one of the trim actuators burn up on a flight last year. Circuit board fried.

[creativewebz]

Definitely clean the friction block under the elevator.

This made a significant difference in trim effort (using wheel to gauge resistance) on our aircraft.

Can someone please describe the cleaning of the friction block under the elevator? My trim wheel seems to be slipping...not all the time or in the same position. sometimes i am moving the wheel and the trim is not moving but the wheel spins.

[michael.g.miller]

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?

[Cschobel]

I bought an overhauled unit and got a trade in of the old unit. Easy for A&P to replace.

[Gearle]

I ended up after all this time needing to replace 2 servos In 2021.