WAAS Airport Costs?

"Ron Rosenfeld" wrote in message
...
On Fri, 18 Feb 2005 07:50:48 -0500, "Eclipsme" wrote:

If so, it looks like over 120 meters
coverage is everywhere. This can't be, can it? What am I missing?

I'm not sure what you are missing. A map reading lesson? Bad color
rendition on your monitor? Perhaps some other issue when you downloaded?

At the present time (1:13 PM EST) it looks like the LPV contour includes
virtually all of CONUS, Alaska, southern Canada, Northern Mexico,
Caribbean
and inside that contour the VPL is 50M or less. For about 99% of the US
it
looks as if the VPL is around 20M.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Well, what I was missing was an understanding of what VPL is. Still not
sure, but at least have an inkling.

Harvey

wrote in message
oups.com...

Eclipsme wrote:
"Ron Rosenfeld" wrote in message
news
On 16 Feb 2005 17:02:23 -0800, wrote:

this does not look like great news for WAAS or LAAS. where is
WAAS
actually functioning right now? (is there a map of applicable
areas?)
or is it "so much for the heavily advertised WAAS features of the
GNS480"?

WAAS usually covers most of CONUS, southern CANADA, northern Mexico
and
Caribbean islands with accuracy sufficient to provide LPV
approaches.

See http://www.nstb.tc.faa.gov/vpl.html for a map that is updated
every
six
minutes.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

What is the 'vertical protection level' on the map? Is this the
altitude (in
meters!) that waas is guaranteed? If so, it looks like over 120
meters
coverage is everywhere. This can't be, can it? What am I missing?

Harvey


VPL is what the receiver compares against a VAL (alert limit) to
determine whether or not to raise the Integrity flag. The VAL for
LNAV/VNAV and LPV is 50 meters.

Regards,
Jon


Thanks,
Harvey

"Dave Butler" wrote in message
news:1108735101.414417@sj-nntpcache-5...
See http://www.nstb.tc.faa.gov/vpl.html for a map that is updated every

six

minutes.

What is the 'vertical protection level' on the map? Is this the altitude
(in
meters!) that waas is guaranteed? If so, it looks like over 120 meters
coverage is everywhere. This can't be, can it? What am I missing?

From the WAAS Terms & Definitions link at the bottom of the page:

Vertical Protection Level (VPL). The Vertical Protection Level is half the
length of a segment on the vertical axis (perpendicular to the horizontal
plane
of WGS-84 ellipsoid), with its center being at the true position, which
describes the region that is assured to contain the indicated vertical
position.
It is based upon the error estimates provided by WAAS.

Ok. I have read this perhaps 6 times. Well, now 8. So it relates to the
probability of my altitude readout being within a certain range of actual.
That may not be quite it, but the chart makes more sense now. There are
areas with more or less uncertainty, which varies over time.

Thanks,
Harvey

On Fri, 18 Feb 2005 21:44:36 -0500, "Eclipsme" wrote:

Well, what I was missing was an understanding of what VPL is. Still not
sure, but at least have an inkling.

Oh. I see your confusion, now. You may think of VPL as indicating the
range of your WAAS enabled GPS altitude indications relative to the true
altitude. So the larger the VPL, the larger the potential error.

The TSO146 certified boxes calculate VPL and, if it is outside some
acceptable range, will limit the type of GPS approaches it will allow you
to conduct.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

"Ron Rosenfeld" wrote in message
...
On Fri, 18 Feb 2005 21:44:36 -0500, "Eclipsme" wrote:

Well, what I was missing was an understanding of what VPL is. Still not
sure, but at least have an inkling.

Oh. I see your confusion, now. You may think of VPL as indicating the
range of your WAAS enabled GPS altitude indications relative to the true
altitude. So the larger the VPL, the larger the potential error.

The TSO146 certified boxes calculate VPL and, if it is outside some
acceptable range, will limit the type of GPS approaches it will allow you
to conduct.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Yes. Thanks Ron for the clarification.. I get it now.

Harvey

The operative word is 'protection' and refers to what the system can
guanrantee it can bound the error to with a very high degree of
certainty. The integrity requirement says that there must be no HMI
99.several 9's% of the time. The actual error will vary (due to
satellite geometry, ionospheric activity, satellite(s) going out of
tolerance or being taken out of service for maintenance). WAAS must
detect and either correct or flag.

For more details than most would probably ever want to know, check out
the Tech Center PAN reports.
http://www.nstb.tc.faa.gov/reports/pan47_1004.pdf for example. Amongst
the plethora of statistics and charts, there's some good explanations
of the phrases being tossed about, such as "protection level" and
"HMI".

Regards,
Jon

Regards,
Jon

Dave Butler writes:
What is the 'vertical protection level' on the map? Is this the altitude (in
meters!) that waas is guaranteed? If so, it looks like over 120 meters
coverage is everywhere. This can't be, can it? What am I missing?

From the WAAS Terms & Definitions link at the bottom of the page:

Vertical Protection Level (VPL). The Vertical Protection Level is half the
length of a segment on the vertical axis (perpendicular to the horizontal plane
of WGS-84 ellipsoid), with its center being at the true position, which
describes the region that is assured to contain the indicated vertical position.
It is based upon the error estimates provided by WAAS.

That certainly clears that up!

Scott Moore wrote:
Bob Gardner wrote:
http://www.avweb.com/newswire/10_18a.../187168-1.html

This will link you to an article that describe LAAS as being
delayed for
quite a while. Don't hold your breath.

Bob Gardner

The principle problem with LAAS is that the government has a schedule
to replace
ALL of the GPS sats with higher precision versions. I.e., the
precision of GPS
is going up, without any particular new infrastructure going into
place on
the ground or in the air.

Actually, a principle problem with LAAS is that the funding was
seriously scaled back.

The CAT I portion of the program was still in the R&D phase, as they
were working the issues (problems with interference/iono, i believe,
were still not resolved).

Which means that by the time any LAAS program got
on its feet, standard GPS, and presumably WAAS, might well offer the
same
capability.

--
Samiam is Scott A. Moore

I'd be sufficiently impressed if WAAS could provide CAT III, even with
dual-frequency, denser network of ground reference stations, algorithm
tweakage etc.

Regards,
Jon

A good place to start is "So you want an Instrument Flight
Procedure..." at:

http://www.avn.faa.gov/index.asp?xml=ifp/index

Regards,
Jon

From the WAAS Terms & Definitions link at the bottom of the page:

Vertical Protection Level (VPL). The Vertical Protection Level is half the
length of a segment on the vertical axis (perpendicular to the horizontal plane
of WGS-84 ellipsoid), with its center being at the true position, which
describes the region that is assured to contain the indicated vertical position.
It is based upon the error estimates provided by WAAS.


That certainly clears that up!

You're welcome. Maybe an example will be more helpful. Suppose that your true
altitude above the WGS-84 ellipsoid is 1000 feet, and the VPL is 100 feet. The
altitude as indicated on your TSO 146 WAAS-enabled navigator is assured to lie
between 900 and 1100 feet. The WGS-84 ellipsoid is the mathematical model of the
earth's surface used in GPS position calculations.