KAP 140 autopilot pitch trim servo clutch slipping?
Posted: Sat Jan 25, 2020 1:09 am
Hello all - Happy Friday
(2004 G1000 DA40 WAAS KAP 140 A/P with altitude pre-select)
Was working on my instrument proficiency today with an instructor and encountered a problem with the autopilot trim. On a coupled approach, the autopilot would not descend quickly enough with a reasonable power setting leading me to be above glide slope. I somehow figured out that the autopilot was not moving the trim wheel forward. I disengaged the A/P and could not move the trim wheel forward with the pitch trim switch. When I move the trim wheel forward and backward by hand, it moves brilliantly with low friction, no stickiness, and it doesn't slip or creep during flight. For these reasons I am reluctant to adjust the pitch trim friction in any way (e. g. loosening it). I re-engaged the autopilot and found that I could move the trim wheel up and down with no complaining or corrections from the autopilot.
I had an a-ha moment:
When I disengage the autopilot, the aircraft will often climb. I think it has been more pronounced lately.
I have been flying the airplane for over three years now, and the autopilot has never held glide slope aggressively. I have to carefully manage the power setting or else it will leave the glide slope - reducing power usually fixes the problem tho I may end up slower than ideal. This is my first sophisticated airplane so I thought this was either normal or the KAP 140 is junk.
There has always been a tremendous amount of backlash on the trim wheel when I pitch trim down with the servo.
The autopilot never gave any error or "trim in motion" today.
I am thinking that the pitch trim servo clutch needs adjusting. I found the section in the manual but the instructions call for a slip clutch test stand and they aren't very clear to me with no diagrams. I am guessing we (my mechanic and I) should use the IPC? I would appreciate any insight into my diagnosis and experience making this repair (should I take it to a specialist)?
(2004 G1000 DA40 WAAS KAP 140 A/P with altitude pre-select)
Was working on my instrument proficiency today with an instructor and encountered a problem with the autopilot trim. On a coupled approach, the autopilot would not descend quickly enough with a reasonable power setting leading me to be above glide slope. I somehow figured out that the autopilot was not moving the trim wheel forward. I disengaged the A/P and could not move the trim wheel forward with the pitch trim switch. When I move the trim wheel forward and backward by hand, it moves brilliantly with low friction, no stickiness, and it doesn't slip or creep during flight. For these reasons I am reluctant to adjust the pitch trim friction in any way (e. g. loosening it). I re-engaged the autopilot and found that I could move the trim wheel up and down with no complaining or corrections from the autopilot.
I had an a-ha moment:
When I disengage the autopilot, the aircraft will often climb. I think it has been more pronounced lately.
I have been flying the airplane for over three years now, and the autopilot has never held glide slope aggressively. I have to carefully manage the power setting or else it will leave the glide slope - reducing power usually fixes the problem tho I may end up slower than ideal. This is my first sophisticated airplane so I thought this was either normal or the KAP 140 is junk.
There has always been a tremendous amount of backlash on the trim wheel when I pitch trim down with the servo.
The autopilot never gave any error or "trim in motion" today.
I am thinking that the pitch trim servo clutch needs adjusting. I found the section in the manual but the instructions call for a slip clutch test stand and they aren't very clear to me with no diagrams. I am guessing we (my mechanic and I) should use the IPC? I would appreciate any insight into my diagnosis and experience making this repair (should I take it to a specialist)?