How true. My KFC225 has failed about a dozen times in 4 years, most of
them without any indication.

Yuck. I knew they were unreliable. I didn't know they were THAT
unreliable.

On one occassion the red Disconnect button failed (this was after the
AP drove the ailerons to full deflection) so the master disconnect had
to be used.

This is the sort of thing I worry about when it comes to autopilots.
Ailerons go hard over at the wrong time, and that's all she wrote.

All this makes a complete joke of TSO-129 certification, which
obviously has no concept of software/hardware quality or reliability.

Eventually, you will come to accept that FAA certification only adds
cost, not value or safety. It's only obvious in those areas where you
know what's going on. In areas where you are ignorant, FAA rules can
seem like a good idea. They never are.

I also hand fly a proportion of approaches, but not all because flying
them (especially an ILS) with the AP is also something that needs to
be done with the correct procedure and that needs practice too.

You know, I've shot a lot of approaches in IMC, including more than one
ILS to real mins (less than 300 ft and less than a mile vis) including
one in a plane I only got into that morning, with an HSI that had
failed and a compass that was unreadable due to a bad light. But the
ILS approach that scared me most was in VMC - with a Century 2000 A/P
flying it. It never seriously occurred to me that I would roll the
plane over just because I was flying with a partial panel at night in
low IMC in an unfamiliar airplane - I always had confidence that it
might not be pretty, but I would either put it on the runway right side
up or make a passable miss. But I knew for a fact that uncommanded
hard rolls are part of life with an autopilot - and frankly my
enthusiasm for low altitude aerobatics on instruments is very low, even
in good VMC. I certainly did not have confidence that I would
successfully recover from such an uncommanded roll - especially if the
disconnect were to fail as well, necessitating fumbling for the rarely
used master disconnect. At 300 AGL my fear got the best of me, I
switched off the AP, and completed the approach by hand - and again,
this was VMC. Risking an uncommanded hard roll at 300 AGL in IMC
strikes me as a last-resort kind of option.

I know the airlines do it - but they're doing it with substantially
better equipment that is maintained far more meticulously.

I have to ask - what was your altitude loss when the ailerons went hard
over and the A/P disconnect failed? What is your logic behind having
it engaged when you are lower than that (assuming you do have it
engaged then)?

Personally, you can't pay me enough to have the autopilot engaged on an
actual IMC approach. I quite agree with you that the procedures
involved require practice, and I do practice with it - under the hood
with a safety pilot I can really trust, and never below 800 AGL.

Michael