KAP140 Autopilot Pitch Fault

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Rich
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Re: KAP140 Autopilot Pitch Fault

Post by Rich »

nrenno wrote: Sun Apr 05, 2020 5:15 pm The KAP 140 of my 2005 DA40 started giving a pitch trim error when booted. After reading the excellent comments in this post and trying some of the simpler steps unsucessfully, I asked my mechanic to remove the pitch trim servo. The servo was sent to Duncan Aviation for repair. They discovered that the servo's strain gauge had failed. The strain gauge was replaced and the service was shipped back me and installed in the plane by my mechanic.

After installation the KAP pilots completes the diagnostics without any error. Everything appears to be working correctly, but when the autopilot is turned on in flight, it pitches the plan down instead of holding the attitude. Does anyone know if this issue can be easily corrected via a laptop connected to the KAP 140?

Thanks!!!
Maybe. There are NULL adjustments for pitch and roll that do not even require the laptop (i.e. terminal) connection. Also, if the flight computer was removed and reinstalled during this process there are these admonitions:

FOR TWO AXIS INSTALLATIONS REMOVAL OF THE KC 140
FROM ITS MOUNTING RACK IN THE AIRCRAFT PANEL OPENS
THE STATIC AIR SYSTEM TO THE AIRCRAFT CABIN. AFTER
REINSTALLATION OF THE KC140, VERIFY THAT THE STATIC
AIR SYSTEM COMPLIES WITH F.A.R. 91.411.

NOTE
The following information is provided in the event that the o--ring on
the KC140 static port requires replacement. The o--ring is 70
durometer EPDMmaterial, AS568A--006 size. The AlliedSignal part
number is 187--01004--0013. The o--ring should be greased with
AlliedSignal part number 016--01210--0000, Dow Corning 55 o--ring
Lubricant (Mil--G--4343) or equivalent grease.

If you can lay your hands on the installation manual you'll see this and other interesting information in section 2.3 regarding setting stuff at initial and re-installation.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Steve
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

nrenno wrote: Sun Apr 05, 2020 5:15 pmDoes anyone know if this issue can be easily corrected via a laptop connected to the KAP 140?
Corrected? Probably not. Diagnosed? Quite possibly. The laptop terminal can read out the error log which is stored in the KAP-140, which can give you a good idea as to what is going wrong.

My KAP-140 exhibited similar behavior (pitching down when engaged) about 18 years ago. This was before I had the capability of connecting with my laptop, but the Avionics shop replaced the KC-140 computer under warranty, which fixed the issue. Good luck,

Steve
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Re: KAP140 Autopilot Pitch Fault

Post by nrenno »

Thank you, Steve! The flight computer was removed. Only the pitch trim servo was removed and serviced.
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Re: KAP140 Autopilot Pitch Fault

Post by Rich »

nrenno wrote: Sun Apr 05, 2020 6:20 pm Thank you, Steve! The flight computer was removed. Only the pitch trim servo was removed and serviced.
The installation manual Section 2.3.3.2 System Offset Adjustments describes, among other items, setting the NULL points for the Pitch and Roll servos. It also includes this paragraph:

This procedure is required whenever the FCC and/or KCM 100 configuration module is/are
removed from the aircraft for servicing and reinstalled, or whenever either component is
replaced.


The pitch and roll servo null point settings are adjusted using the potentiometer in the face of the FCC. One sets the voltage across a couple of the pins in the connectors to zero while the AP is in the appropriate mode.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: KAP140 Autopilot Pitch Fault

Post by nrenno »

Thank you, Steve!
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Re: KAP140 Autopilot Pitch Fault

Post by jehan »

Hi,
This morning, I was doing the ramp checks and while doing the usual autopilot checks with VS plus and minus to see if the stick is properly moving, I noticed that the trim wheel started moving. The trim wheel was all the way back. After disconnecting form A/P, I tried to bring the trim wheel back to T/O position but it was not working. It was continuously slipping. I even tried to move the trim back by using the push buttons on the stick but it was continuously slipping. What might have gone wrong and how one can fix it. thanks
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Re: KAP140 Autopilot Pitch Fault

Post by Rich »

jehan wrote: Mon Dec 27, 2021 7:43 pm Hi,
This morning, I was doing the ramp checks and while doing the usual autopilot checks with VS plus and minus to see if the stick is properly moving, I noticed that the trim wheel started moving. The trim wheel was all the way back. After disconnecting form A/P, I tried to bring the trim wheel back to T/O position but it was not working. It was continuously slipping. I even tried to move the trim back by using the push buttons on the stick but it was continuously slipping. What might have gone wrong and how one can fix it. thanks
It sounds like maybe the gearing/cable linkage in the trim wheel assembly may have gone "over center". I would remove the pilot seat so you can get at the linkage and try to simultaneously push downward on the cable fitting while working the trim wheel. All manually, of course. The AMM describes how to properly set the limits of travel to prevent this. Yours may be off.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: KAP140 Autopilot Pitch Fault

Post by Rich »

Rich wrote: Mon Dec 27, 2021 9:58 pm
jehan wrote: Mon Dec 27, 2021 7:43 pm Hi,
This morning, I was doing the ramp checks and while doing the usual autopilot checks with VS plus and minus to see if the stick is properly moving, I noticed that the trim wheel started moving. The trim wheel was all the way back. After disconnecting form A/P, I tried to bring the trim wheel back to T/O position but it was not working. It was continuously slipping. I even tried to move the trim back by using the push buttons on the stick but it was continuously slipping. What might have gone wrong and how one can fix it. thanks
It sounds like maybe the gearing/cable linkage in the trim wheel assembly may have gone "over center". I would remove the pilot seat so you can get at the linkage and try to simultaneously push downward on the cable fitting while working the trim wheel. All manually, of course. The AMM describes how to properly set the limits of travel to prevent this. Yours may be off.
Upon further review - it doesn't look like an over-center condition is reasonable. But it does seem possible that the "gear segment" could be jammed against a stop.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: KAP140 Autopilot Pitch Fault

Post by jehan »

Thanks Rich,
Later in the afternoon, I gathered some more facts. When I parked the plane I visually inspected the trim tab and elevator. While doing so I inadvertently moved the elevator with the trim tab (just like we do in pre-flight). When I returned back in the afternoon, I noticed that I was able to move the trim wheel back to the T/O position without any major effort. However, at this stage I was not able to connect the dots. Thereafter, I rolled the trim wheel manually back to the most after position and then I was anticipating that I will be able to rotate it back with no effort (assuming as if the problem is somehow fixed and may be the trim actuator might have caused the issue). But no I was again at the same point i.e. the wheel was not moving. Then I walked back to the tail section to see if there anything I can see and my hands as usual reached out to the elevator plus trim tab. When I came back to the cockpit and tried the wheel this time, it was again freely moving.
Hence, it appear that what do described: the gear segment could be jammed against a stop
is a strong possibility. I am believe I need to remove the seat and the center console to reach this particular section and see if that is the case. I wish there was a video of this task. I am going to make one and post it.
Once gain thank you.
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Re: KAP140 Autopilot Pitch Fault

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jehan wrote: Tue Dec 28, 2021 8:06 pm is a strong possibility. I am believe I need to remove the seat and the center console to reach this particular section and see if that is the case. I wish there was a video of this task. I am going to make one and post it.
Once gain thank you.
Having done this a billion times (slight exaggeration) I can get a front seat out in about 5 minutes. Some hints:
- 4 bolts (10mm heads) along the front. Mine used to be hidden behind the front flap of the front seat leather. I don't know if yours is like that, but it's definitely an obstruction. I finally cut this section free so the cushion and these 4 bolts can be easily removed.
- 2 bolts (13 mm heads) hold the rear brackets for each seat in place, facing horizontal. You have to wrestle the carpet-enclosure for the rear seat heat vents out of the way.
- After removing the rear bolts rotate each of the two brackets inward a couple of inches, toward each other.
- Before removing either seat I fasten its seat belt into the latch. This is to help to avoid problem with reinstalling.
- Note: To remove the copilot seat push the mixture control forward. (Be sure not to rotate the prop while this is the case or you will wind up with fuel on the floor.)
- When removing a seat tilt it toward the center a bit.
- I find that the seat belts are long enough that you can set the seat on the floor of the hangar with the belt still attached.

When reinserting, you reverse the procedure somewhat.
- Wrestle the seat back into position. Tilt inward as with removal.
- Push the rear brackets back into position (the heat vent will want to get into the way) and get each of those large bolts well started. Getting these lined up can be a chore. It is helpful that these brackets have slots rather than round holes. Moving the seat around while doing this is helpful. Typically I use a shoulder to kind of lift up the rear of the seat.
- With the rear seat bolts started, reinstall the 4 front seat bolts. Get them all started before snugging down. Getting these lined up is also a challenge. Wriggling the front of the seat helps. Once they're all properly started, tighten them all down.
- Finish tightening the rear seat bolts and push the vent back into position.
- If the copilot seat was removed, set the mixture back to idle cutoff.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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