KFC200 diving on alt hold

[Pierre07]

Hi all,

I have a 1981 231 with a KFC200 in that always worked good since I bought it last year. Last flight, I was climbing with A/P on tracking NAV and everything was fine until I hit the alt hold button and then it instantly started diving so I turned everything off and tried it again, did the same exact thing. Even when I’m already all trimmed and flying level, as soon as I hit the Alt Hold, the FD is going straight down and the A/P is chasing is so diving really fast.

Anyone on here had that problem before and could help??

Thanks in advance!!

 

 

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[Alan Fox]

usually the horizon KI258

[anthonydesmet]

@Pierre07i know on my 80 231 with KFC 200 I have to deselect and reselect Alt Hold at my new altitude before I select autopilot back ON.  If I don’t the autopilot will dive back down to preceding altitude and the FD will show it.  
This might be a what you are already doing but I couldn’t tell from your description above so thought I would offer this up.

[Pierre07]

Thanks Anthony!
Yeah I didn’t say that in the description, I have to do the same on mine once you go from one altitude to another. But in this case, it’s doing it on the first time I select altitude hold.
Right after my initial climb once I get to cruising altitude. Even if I trim it so it’s flying level and then hit alt hold, it dives.


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[Jake@BevanAviation]

@Pierre07Sounds like the alt hold board has some issues, possible transducer failure.  Normally when they fail they drive hard up or hard down but always the same direction, fast and aggressive.  There is a slight possibility the static line to the transducer could be plugged.  You can unhook the line and try selecting alt hold on the ground with the gyro close to level and FD mode active.  If the bars drop rapidly my guess is there is a fault in the flight computer.  If you can use the vertical modifier in the control head to set a climb or descent and the aircraft maintains that attitude most of the system is working.  If using CWS to establish level flight with everything in trim and then you add in ALT hold the FD bars deviate and the computer chases, everything points to the alt hold board.

Edited October 14, 2021 by Jake@BevanAviation