KAP140 Autopilot Pitch Fault

[Steve]

Rich:

You have all of the stigmata of a chronic seat remover-installer. Reading your instructions had me breaking out in a cold sweat, since I suffer from the same condition (slightly worse, since I've done mine 1.12 billion times). I think that I suffer from PTSD (Post-Traumatic Seat Disorder).



Steve

[Rich]

Try one other thing, Jehan. With the trim wheel in its stuck state, try pushing the stick all the way forward when trying to move the trim wheel. I've noted that the trim starts to get somewhat sticky with the stick vertical or fully back, particularly if the trim friction block is a bit contaminated.

[jehan]

Thanks Rich,

I will test the "trim wheel in stuck state, try pushing the stick all the way forward when trying to move the trim wheel."

Here is the image of the mechanism from IPC. Just wanted to confirm if the "gear segment" is referring to the chain-sprocket piece of hardware.

thanks,

Jehan

[jehan]

One question with regards to the functioning of KAP140. As I understand there are all together 3 servos i.e. Roll servo, Pitch servo and Pitch Trim servo. When we are doing autopilot test on the ground, for Roll servo (since it is only one) it is clear that the heading bug will help move this one and as a result the stick will appear to move laterally. When it comes to pitch test... we have two servos. If memory serves, before this problem that I reported the whole stick was moving i.e. the pitch servo was in motion. However, on this particular day, I noticed instead of the stick, the pitch trim servo was in motion, i.e. the trim wheel started moving. So the question is: have I done something that demanded the pitch trim servo to move instead of the pitch servo to act? I understand pitch servo is coarse control as compared to pitch trim servo. I will appreciate if you can shed some light on this topic. Thanks

[Rich]

Thanks Rich,

I will test the "trim wheel in stuck state, try pushing the stick all the way forward when trying to move the trim wheel."

Here is the image of the mechanism from IPC. Just wanted to confirm if the "gear segment" is referring to the chain-sprocket piece of hardware.
pitch trim assembly.png
thanks,

Jehan

No, it's the part on the opposite side. Get rev 8 (current) of the AMM and check out section 27-38-00, especially page 7, paragraph 3, where there is a really excellent description of this operation.

[Rich]

One question with regards to the functioning of KAP140. As I understand there are all together 3 servos i.e. Roll servo, Pitch servo and Pitch Trim servo. When we are doing autopilot test on the ground, for Roll servo (since it is only one) it is clear that the heading bug will help move this one and as a result the stick will appear to move laterally. When it comes to pitch test... we have two servos. If memory serves, before this problem that I reported the whole stick was moving i.e. the pitch servo was in motion. However, on this particular day, I noticed instead of the stick, the pitch trim servo was in motion, i.e. the trim wheel started moving. So the question is: have I done something that demanded the pitch trim servo to move instead of the pitch servo to act? I understand pitch servo is coarse control as compared to pitch trim servo. I will appreciate if you can shed some light on this topic. Thanks

Hard to say. Basically the pitch and pitch-trim servos work together with the FC and try to maintain VS or ALT. When on the ground and the plane really can not react to the desired commands it's anybody's guess what the the AP decides what is necessary. I have observed this myself when checking the AP on the ground.

[jehan]

Thanks Rich,

I will test the "trim wheel in stuck state, try pushing the stick all the way forward when trying to move the trim wheel."

Here is the image of the mechanism from IPC. Just wanted to confirm if the "gear segment" is referring to the chain-sprocket piece of hardware.
pitch trim assembly.png
thanks,

Jehan

No, it's the part on the opposite side. Get rev 8 (current) of the AMM and check out section 27-38-00, especially page 7, paragraph 3, where there is a really excellent description of this operation.

Thanks,

Please see if this drawing makes sense in light of page 7 paragraph 3.

Thanks,

Jehan

[Rich]

Thanks Rich,

I will test the "trim wheel in stuck state, try pushing the stick all the way forward when trying to move the trim wheel."

Here is the image of the mechanism from IPC. Just wanted to confirm if the "gear segment" is referring to the chain-sprocket piece of hardware.
pitch trim assembly.png
thanks,

Jehan

No, it's the part on the opposite side. Get rev 8 (current) of the AMM and check out section 27-38-00, especially page 7, paragraph 3, where there is a really excellent description of this operation.

Thanks,

Please see if this drawing makes sense in light of page 7 paragraph 3.

pitch trim assembly v2.png

Thanks,

Jehan

It's correct for nose-down trim. Remember, trim-tab movement is opposite to what it causes in the elevator.