On Tue, 16 Dec 2008 11:44:19 -0800, Andy wrote:

Thanks for the tip but this is a PA28-180 with an alternator. Problem
was intermittent last winter, gone in the summer, and back again now
winter is here. I'm in the middle of some cold soak testing but results
so far point to the encoder (ACK A-30).

I have no experience with aircraft with engines. But it seems these
encoders can put out nonsense flight level data. Your experience -
Winter, mine - dying battery, seem to indicate that it does this when it
is not warm enough.

Whatever the fix, it is worth knowing that this can happen. Does yours
come right once it has been running a while?

Ian