On Thu, 17 Jul 2003 14:32:39 -0500, Big John
wrote in Message-Id: :

Last issue of AW&ST has article stating "Following a three-year delay
to correct software problems, the FAA has commissioned the Wide Area
Augmentation System (WAAS) to refine GPS guidance for en route and
approaches"..........................

"It will take years for the FAA to design and certify approaches to
runways at the current rate of about 300 per year." ..................

"by using WAAS and GPS as the sole means of navigation, aircraft can
operate lower and still be safely above terrain and
obstacles."........

"Dan Hanlon, FAA's WAAS program manager, emphasized that the two key
benefits that WAAS has over GPS are vertical guidance and improved
availability of signals"..............

"the FAA has spent $886 million on WAAS to date" ....................

So now you know )

Big John.


Here's a little more information from GPS mailing list:


Return-path:
Date: Thu, 10 Jul 2003 10:45:52 -0400 (EDT)
From: Bob Siegfried
Subject: WAAS
To:
Reply-to: GPS for Aviation
Message-id:

In a message dated 7/10/03 8:52:24 AM Central Daylight Time,
writes:

The FAA flicked the switch on the Wide Area Augmentation System (WAAS)
signal, a crucial first step on the way to highly accurate satellite-based
navigation in the U.S. "We're just waiting for the avionics to catch up," said FAA
spokesman Greg Martin.

Good Morning George,

That is good news, but it is tempered by the way the data is being
implemented.

The FAA is currently enamored with building ILS look alike approaches
using WAAS.

That sounds good. The trouble is that an "ILS Look Alike Approach"
via WAAS only provides the airborne guidance. Without a suitable
obstacle environment and approach lighting, the guidance can actually
be detrimental to GA operations.

How so? If the obstacle environment is such that a DH of five or six
hundred feet results, there will be a a visibility minima that will
allow visual sighting of the runway when the aircraft is at the DH.
That can mean that a 600 foot DH will require over two miles
visibility.

That doesn't sound all that bad, except that a non precision approach
to the same runway will likely have a minimum required visibility of
one mile.

To the FAA's credit, they are generally providing an LNAV approach
along with the VNAV that does take advantage of the lower visibility
requirement.

The rub comes with the circling minima.

The FAA has a policy that when there are two approaches on the same
approach plate, the circling minima can be no lower than the highest
required visibility for any approach shown on that approach plate.

That means that an approach which would otherwise have circling
minimums of 600 and one will be stuck with a circling minima of six
hundred and two merely because there is a VNAV approach designated for
that runway.

I could provide many examples where we are losing considerable
operational capability due to this anomaly. Unfortunately, I have to
run and can't spend the time right now, but if anyone is interested, I
do have some horrible examples in my files. (If I can find them that
is!)

It is shame that implementation of the WAAS is causing our minimums to
go up.

The worst thing is that nobody seems to care!

Happy Skies,

Old Bob