Pgbnh,

What is your favorite AP

S-TEC. Hard to find more cost-efficient retrofits. The 20/30 (if panel
space is an issue, those are completely contained in a turn
coordinator) or the 40/50 come to mind.

Thoughts on 2 v 3 axis

Let's properly define it first:
1 axis is wing levelling including possibly NAV and GPS tracking and
possibly intercepts of desired tracks/radials. This mostly includes
following localizers in an "approach mode".
2 axis includes altitude hold.
3 axis means an additional yaw damper for some, and altitude preselect
and capturing for others. THe latter mostly includes the ability to
follow glide slopes.

You probably don't want more than 2-axis

Features to look for

Well, with a 530, you'll want GPSS. That's GPS roll steering and means
that the GPS drives the autopilot in a more efficient way than just
like a CDI. That will give you turn anticipation and other neat stuff.

Also, you'll need to be aware of the difference between rate-based and
attitude-based autopilots. Most rate-based APs operate with electric
turn coordinators. This means they will continue working when your
vacuum system or your AI fail. Which some (myself included) consider an
important safety feature.


--
Thomas Borchert (EDDH)