Hello All,

The STEC 55 autopilot on my IVP is not responding to treatment and I'm
wondering if others have had the same symptoms or can add some light to this
murky (to me) subject.  Its problems are that the Nav function is
alternatively lazy or totally nonfunctional above 14,000 feet.  Also, as the
altitude increases, the Heading function gets progressively less able to
manage the control forces that the Heading bug says are needed.  This
doesn't happen until the Flight Levels.  One obvious conclusion is that the
servos are not able to exert enough force to follow the control commands.
But I'm wondering whether there is more to it than that, or, if that is the
case, what the fix is.  I have had the computer and associated bits in the
"black box" checked and the software updated at STEC.  They  have also just
cleaned and serviced the servos.  Interestingly, both Altitude Hold and
Vertical Speed cfunctions seem to work properly.  I do not have Altitude
Preselect or GPSS features.  I remember reading that this type of problem
was one reason some IV pilots were selecting TruTrak instead of STEC, but I
can't find those postings.  Any information will be much appreciated.


Jack Cowell
N177ME, 1100 hours