On Apr 1, 6:31 am, "Viperdoc" wrote:
I went and did some LNAV/VNAV approaches yesterday with a King KFC 200
autopilot. Looking for some tips with these autopilots on GPS approaches.

1. In NAV or APP mode the commanded rate of turn appears slower than in
HEADING mode. Spinning the HSI to the desired heading (often 90 degree
turns) caused the plane to try to go in the wrong direction, or the rate of
turn (slightly less than standard) caused an overshoot and didn't capture
the new course.

It's true. The rate of turn is somewhat reduced. Shouldn't turn the
wrong
direction unless turning 180 degrees. If you start the turn as
commanded by
the GPS, it will make it. If it goes the wrong way on a 90, there is
something
wrong with it.

2. If flying in APP mode, and then making a step down in altitude, the AP
would not capture the glideslope (I've noticed this with ILS approaches as
well, even if intercepting the GS from below)

If it's working right, it should intercept the gs from either attitude
mode or
altitude mode. The gs must pass thru center in either case and it may
be
slightly misadjusted. Descending onto it from above requires a
serious rate
of descent and it could be argued as unsafe.

3. Of course, roll steering would be ideal, but barring this, is there a
better way to utilized the autopilot to fly these approaches?

Most of the dozens of KFC200s I've run into at BPPP clinics track just
fine
by turning the course arrow as commanded by the GPS. If you have a
sandel,
this is done automatically for you. Note that in strong winds, after
a 90
degree turn your ap will have to re-psych the wind; if you use APR
mode this will
be fairly rapid.

4. Would it be better to fly in heading mode, and then engage approach mode
just prior to the FAF?

That would work. There are a lot of features in the coupling modes of
the 200.
In some cases if something isn't working right it would be really hard
to detect.
It's all analog switches driven by combinational logic. I'm sure that
some I've
seen aren't working correctly because the vast majority of them do the
problem
correctly.

Bill Hale BPPP instructor