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It may be that an electrical malfunction sort of
"runaway trim" situation is unlikely but I think there is more to the
story. Here are a few disconcerting issues I've found on my
airplane:
0) HPAT made me fly with max pitch up trim at
speed. I don't think I would like this at all IMC at 25000 and
needing to get down. For that condition you want lower
airspeed which would mean losing pressurization, prolonged descent time,
etc. I didn't try max pitch down but according to my test pilot
report that looks like it would be even more challenging on
approach.
1) I have dual trim control (pilot and copilot)
with a disable on the copilot. I had a condition early on that
turning OFF the copilot trim cause d the auto-pilot to do weird
things. It turned out the copilot auto-pilot disable was stuck
ON. since the sorcerer is looking for a transition (bad idea IMO) it saw
the transition to OFF as a toggle. ...which could mean a/p off, a/p
on, or cws depending. I sanded the parts and
decided to live with it. but generally that copilot disable only moves on
the ground.
2) the RAC system wants 12V so I run it from my 12V
power converter. That makes my power converter part of my safety of
flight. I don't like that in the first place. ...but one day
the 12V supply CB popped, killing my trim. It's never done it
before or since. I really don't like the fact that RAC doesn't
make a 28V part. I've considered dual redundant and dedicated power
supplies just for the trim.
3) My pitch trim servo installation was customized
to use a shorter lever so as to be aerodynamically cleaner. This results
in it having more travel that it needs. I've purchased parts to
reduce travel.
4) RAC relays don't seem to last very
long.
5) I have a/p auto-trim on my airplane.
Although I haven't experienced it on this airplane, I have experienced the a/p
dialing in a heap of trim and then disconnecting. This is attention
getting in a cessna. Right now my a/p auto-trim is always on
disable.
So although there may not be a likely runaway
situation with RAC components alone, there are still lots of ways for the trim
to end up where you don't want it, and possibly without the ability to fix
it. dual redundant 28V trim servos, or manual trim would be
nice.
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