Need KFC 200 Help

[Geoff]

My KFC 200 is making uncommanded turns intermitently while coupled in any mode (NAV, HDG, LOC).  I had the AI overhauled (it needed to be done for other reasons as well) and this did not solve the issue.

My next thought was to go through all the connections and clean them.  Has anyone else had this experience?

[Piloto]

Quote: Geoff

My next thought was to go through all the connections and clean them.  Has anyone else had this experience?

[jlunseth]

Not with my KFC 200, but the flight school where I got my instrument had this problem with the AP in a Skyhawk.  It was not a King at all, don't remember the manufacturer.  I don't remember the issue very well, but I think the cause was actually in the HSI.  I believe the AP relies on the HSI for directional information, i.e. what direction am I going and which way do I want to go.  So if the HSI suddenly precesses too much, it confuses the AP.  That seemed to be what was going on with the Skyhawk.  Periodic, sudden large precesses.

[Geoff]

You are right about the HSI providing directional information to the AP, However, the HSI is functioning just fine and does not precess, otherwise I would suspect the flux gate.

[N201MKTurbo]

Even if the gyro is solid, the electrical pickup could be intermittent.

[FlyDave]

A few months ago I had the AI on my KFC-200 rebuilt and the autopilot turned right of course after the AI was re-installed.

It turns out that you have to have the autopilot re-calibrated to the AI when it's rebuilt. They also found that the HSI needed to be adjusted when re-calibrating the AP.

My cost was $1600 to re-build the AI and $950 for the AP calibration HSI adjustment. My AP works just fine now.

[carusoam]

Geoff,

What is driving the nav function....?  GPS, VOR or both.

Does the uncommanded roll occur on nav source or both?

I had a nav radio send enough data to the HSI to not flag the nav, CDI was centered (always) but the A/P was not tracking anything.  Just wings level and drifting.

[Geoff]

Thanks everybody for your thoughts, I really appreciate it...

The uncommanded roll occurs on both GPS and VOR/ILS sources.  The GPS/VOR source for both is a 430W.  The strange thing is that this only happens intermittently.  It will track VOR/GPS/ILS great for hours and then suddenly make a turn left or right.  If I'm awake, I catch it, press the CWS button on the yoke and point the plane back in the right direction and then release the CWS button and the AP gets it right again.  Its like the AP is having a "senior moment" and needs a reminder of what it was doing.

This makes flying approaches in low IFR um... interesting and I'd like to get it fixed.  The side benefit is my instrument cross scan hasn't been this good since my last IPC.

Interesting that the AP has to be recalibrated.  I was having the same problem prior to the rebuild of the AI.  I'll ask the avionics guys about that.

[roundout]

I've seen 200 series do stuff like this before. It's annoying. Cleaning the connections certainly might get you on track but it might not. i'd try that first because it's easy and cheap. If it doesn't work, move on to other options. 

[rogerl]

Quote: Geoff

Thanks everybody for your thoughts, I really appreciate it...

The uncommanded roll occurs on both GPS and VOR/ILS sources.  The GPS/VOR source for both is a 430W.  The strange thing is that this only happens intermittently.  It will track VOR/GPS/ILS great for hours and then suddenly make a turn left or right.  If I'm awake, I catch it, press the CWS button on the yoke and point the plane back in the right direction and then release the CWS button and the AP gets it right again.  Its like the AP is having a "senior moment" and needs a reminder of what it was doing.

This makes flying approaches in low IFR um... interesting and I'd like to get it fixed.  The side benefit is my instrument cross scan hasn't been this good since my last IPC.

Interesting that the AP has to be recalibrated.  I was having the same problem prior to the rebuild of the AI.  I'll ask the avionics guys about that.

[jlunseth]

The flux gate drives the HSI, which drives the AP.  There is a connector to the flux gate in the wing that seems to need periodic cleaning, or the signal from the flux gate gets interrupted.  Sorry, I do not know where in the wing it is because I had it cleaned, did not clean it myself.  From what I was told, it is a not uncommon issue with the HSI.