Century 31 altitude hold issue

[bnicolette]

Hello all,

I have a Century 31 A/P and flying back from Wilmington, De today the altitude hold feature started to act up.  It attempted to hold altitude, but it was very twitchy (for lack of a better word).  It also seemed to be twitchy in the pitch mode?  Does anybody or has anybody had this issue with this autopilot that would be willing to point me in the right direction?  It started about an hour into the flight and I didn't let it continue very long then I just hand flew it.  I engaged it again later in the flight with the same results.

[Piloto]

I had the same problem and here is what I found:

After 10 years or more the attitude gyro contacts needs to be cleaned. On the back of the attitude gyro there is a small cover held by three screws. Remove the cover. You will see a shaft in contact with four hair contacts. Spray contact cleaner into the shaft to clean the contacts. Do not touch the shaft or the hair contatcts. Re attach the cover and screws. This job is better done with the gyro removed from the panel but it can be done in the panel, just make shure you put a rag underneath the gyro to catch the inevitable falling screws. After cleaning the contatcts fly the plane performing rolling maneuvers to wipe the contacts.

José

  

 

[bnicolette]

Jose,

Thank you for the suggestion.  As luck would have it, I took the plane out this morning and everything was working well????  I will keep that in mind if it should happen again though.  I'm not sure if that was what was going on as I just put a brand new (well newly overhauled) attitude indicator in two weeks ago, but that doesn't mean that it should be trouble free, I would just hope it would.

[John Pleisse]

Jose is dead on. I also found Mooney panel vibration caused the AI contacts to literally come loose. My avionics guy mod'ed his crimping to keep it from happening again. My C3-C eventually needed a new altitude can. I went with stec and never had an issue. Also, have the mother board opened and checked. I have heard stories of mother board corrosion from moist environment or corrosive battery gasses nearby in the tail cone. Corrosion in my mother board instigated the Stec 55X upgrade.