KAP140 Autopilot Pitch Fault

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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: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

nrenno wrote:
Sun Apr 05, 2020 5:15 pm
Does 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,

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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: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: KAP140 Autopilot Pitch Fault

Post by nrenno »

Thank you, Steve!
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