scott moore wrote in news:-
:

Now that the WAAS minimums are going to be 200, same as
ILS, and the first WAAS approaches are going to be
overlaid over standard ILS approaches, the question
arises:

Which approach makes more sense to an ILS runway, use
of the ILS, or the WAAS?

Before you say "good ole ILS", consider: WAAS is going
to have many characteristics of an ideal precision system.
No false glideslopes, infinite range, no backcourse image,
etc.

One feature of the GPS approach that I like is that the sensitivity stays
the same all the way down; it doesn't increase as you get closer to the
runway. You have a chance to get used to a sensitivity, and use it
throughout the approach. GPS accuracy is better than a localizer anyway,
and if the vertical accuracy is sufficient using WAAS, then I'll take a
GPS approach every time.

I recently had a chance to fly GPS approaches with vertical guidance in
the S76C+ sim at Flight Safety in West Palm. It's just like flying an
ILS, with a glideslope indicator, and it's a really good idea. No dive
and drive, you set up a stabilized approach profile and when you break
out you just continue and land, no need to change anything. The lower
the DA/MDA, the more important this becomes. GPS, if the needles are
centered, brings you over the runway centerline, every time. A localizer
will bring you more or less over the runway, but not always. There can
be bends in it, especially if another aircraft gets into the wrong place.
I know of one ILS in south Louisiana that consistently brings you down
the right-hand edge of the runway. GPS will put you on the center, every
time, and that's important if you're going to break out below 200'.
Remember, you can continue to 100' above the TDZE with only the approach
lights in sight, and that's common for us, using 1/4 mile vis minimums in
helicopters. You may actually get the runway in sight at 100', and you
really need to be over the runway center there, not out over the edge.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin