Fast forward to the future: WAAS 200 minimums

[scott moore]

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.

[Nathan Young]

On Fri, 10 Mar 2006 04:34:29 -0800, scott moore >
wrote:

>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.

Although my aircraft isn't so equipped (yet) - WAAS.

WAAS + a GPSS equipped A/P would have the ability to steer you from
cruise to the DH.

Question: When a WAAS and ILS approach co-exist for the same runway,
does the FAA make the WAAS approach so it is an exact overlay of the
ILS? It would be nice to run the WAAS approach on the GPS, and have
NAV2 tracking the ILS as a backup.

[Dave Butler]

scott moore wrote:
> 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.

....and seamless transition from enroute to approach environment, no tuning, no
identifying, no switching indicators from one nav source to another.

[Stan Gosnell]

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

[scott moore]

Nathan Young wrote:
> On Fri, 10 Mar 2006 04:34:29 -0800, scott moore >
> wrote:
>
>> 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.
>
> Although my aircraft isn't so equipped (yet) - WAAS.
>
> WAAS + a GPSS equipped A/P would have the ability to steer you from
> cruise to the DH.
>
> Question: When a WAAS and ILS approach co-exist for the same runway,
> does the FAA make the WAAS approach so it is an exact overlay of the
> ILS? It would be nice to run the WAAS approach on the GPS, and have
> NAV2 tracking the ILS as a backup.

From the Aopa article on the same subject, I gather it is, but I
could be interpreting it wrong (it does not go into it in much
detail):

http://www.aopa.org/whatsnew/newsitems/2006/060307waas.html

I have used the 2nd radio LOC to follow a GPS approach, they seem to
track as you would expect, that is, close, but not identical, perhaps
a half dot off.

I'd like to do the 2nd ILS monitor thing as well, but it would require
an upgrade to my 2nd radio, which is the crappy original ARC radio
without a glideslope.

[JPH]

Nathan Young wrote:
> On Fri, 10 Mar 2006 04:34:29 -0800, scott moore >
> wrote:
>

>
> Question: When a WAAS and ILS approach co-exist for the same runway,
> does the FAA make the WAAS approach so it is an exact overlay of the
> ILS? It would be nice to run the WAAS approach on the GPS, and have
> NAV2 tracking the ILS as a backup.

The FAA policy is to duplicate the ILS when possible, to include
glidepath angle, TCH, and intercept altitude. The goal is to have the
same fixes shared by the ILS and LAAS. Missed approach criteria is
different for LAAS than for ILS, so there are times that the missed
approach can't be duplicated because the ILS missed approach turns too
much or too soon.
See para 491b at the following link for particulars;
http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs400/afs420/policies_guidance/orders/media/8260.19C%20CHG3.pdf

JPH