"Al" wrote in
:

Some autopilot failures are very subtle. I was shooting a coupled ILS
to minimums with a King autopilot in a Mooney. After capturing the
glideslope, I noticed the rate was about 75'/min more than I was used
to. As we got closer to DH, the DME was still showing about 2 miles to
the airport. I leveled at DH, and while motoring along 200' above the
houses, I tapped the Vor/loc. The GS needle snapped to the top of the
case. It was "stuck" centered, and the autopilot
was literally flying the needle. Iron Mike, indeed.

Technically speaking, that wasn't an autopilot failure, it was a GS needle
failure. The results would have been nearly identical if you were hand-
flying. Although you might have noticed inconcistencies in airplane
response more quickly and fixed it earlier. Then again, you might have been
so busy keeping the needle centered that it would have gone unnoticed until
you flew your plane right through someone's living room.

Hard to say.