I had a failure like this. It wasn't the computer but one of two
transistors in the location of the servo. The avionics guy told me they
each process (?) turning signals and sort of balance each other out for
level flight. If one goes, the other is free to bank the plane without a
signal from the broken one to bring it back. Now his explaination wasn't
the best and this was many years ago.....but that was my experience. In
my situation, it would bank and never level out, I imagine I punched it
off about 30 degrees or so, but it would have kept going. On the ground
you can demonstrate the failure with the heading bug.

But I have a seneca with a king autopilot and the parts were under the
seats, computer in the tailcone.

In case it helps..

John

William Snow wrote:
I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would like
to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow