Ron,

As Jim says, there's advice on that in the POH. Keep in mind that the
S-TEC 50 does not intercept/capture radials or localizers. You have to
get the plane onto the localizer (which can of course be done with the
AP in heading mode). Only after that you can engage the approach mode.
Main difference between approach and nav is the sensitivity. With the
S-TEC 50, you will still have to manage the altitude profile yourself.

I have seen vastly different accuracy on different installations in
different aircraft with the S-TEC 50. On our Tobago, it can be used
well on approaches down to 200 feet.

--
Thomas Borchert (EDDH)