I have the ear of some local government development people, who are
contemplating upgrading some airports. Money is tight, so an ILS is
probably not under consideration. So, I want to recommend to them
checking into a WAAS installation. Does anyone know what the prices of
such equipment for an airport are, which companies are selling them,
and how much it costs to get the FAA to then create a WAAS IFR
approach?

Sincerely,

/iaw

There is no airport equipment required for WAAS. You are probably thinking
of LAAS.

But, if the airports don't meet current FAA standards for IFR runways and
taxiways, then there can be modest costs for runway markings, or
significant costs to bring the pavement into compliance.

It is a very complicated mix, but since the airports are owned by local
government, they should have a knowledable airport engineer on the airport
staff who is already up to speed on the airport advisory circular
requirements, and what the FAA regional airports division expects.

wrote:

> I have the ear of some local government development people, who are
> contemplating upgrading some airports. Money is tight, so an ILS is
> probably not under consideration. So, I want to recommend to them
> checking into a WAAS installation. Does anyone know what the prices of
> such equipment for an airport are, which companies are selling them,
> and how much it costs to get the FAA to then create a WAAS IFR
> approach?
>
> Sincerely,
>
> /iaw

Is there any airport equipment required? I thought WAAS is a regional
thing. We have WAAS for Sacramento and the San Fransico bay area. I
think they call it LAAS if its at an airport. In any case, I believe
the cost you are looking at is the design of the approach. However, the
FAA often covers that if you can show enough need.

-Robert

wrote:
> I have the ear of some local government development people, who are
> contemplating upgrading some airports. Money is tight, so an ILS is
> probably not under consideration. So, I want to recommend to them
> checking into a WAAS installation. Does anyone know what the prices of
> such equipment for an airport are, which companies are selling them,
> and how much it costs to get the FAA to then create a WAAS IFR
> approach?

There's no ground equipment requirement, all the equipment is airborne. All you
have to do is convince the feds to commission the approach. Talk to your
congressperson. I suppose it's possible you might need to get some obstructions
removed, or something like that, in order to get the approach commissioned.

Dave Butler > wrote:

> wrote:
>> I have the ear of some local government development people, who are
>> contemplating upgrading some airports. Money is tight, so an ILS is
>> probably not under consideration. So, I want to recommend to them
>> checking into a WAAS installation. Does anyone know what the prices of
>> such equipment for an airport are, which companies are selling them,
>> and how much it costs to get the FAA to then create a WAAS IFR
>> approach?
>
> There's no ground equipment requirement, all the equipment is airborne.

If the airport is not currently equipped for instrument landings, wouldn't
it require approach lighting and proper runway markings?

--
Peter













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On 15 Feb 2005 10:58:03 -0800, wrote:

>I have the ear of some local government development people, who are
>contemplating upgrading some airports. Money is tight, so an ILS is
>probably not under consideration. So, I want to recommend to them
>checking into a WAAS installation. Does anyone know what the prices of
>such equipment for an airport are, which companies are selling them,
>and how much it costs to get the FAA to then create a WAAS IFR
>approach?
>
>Sincerely,
>
>/iaw

There is no WAAS specific equipment for the airport to purchase. However,
the airport does have to meet the criteria for an instrument approach of
the type being contemplated. Depending on the type of approach, this may
include surveying for obstacle-free zones; lighting; or even a parallel
taxiway. Government funds are frequently available, and may cover 90+% of
the costs.


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

"Peter R." wrote:

> If the airport is not currently equipped for instrument landings, wouldn't
> it require approach lighting and proper runway markings?
>

Approach lighting is always optional.

> Government funds are frequently available, and may cover 90+% of
> the costs.

That money pot is rapidly drying up with dollars flying to Iraq and other such
declines in the American Empire.

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

Robert,

> Is there any airport equipment required?

There are requirements for runway markings and lightings for IFR
approaches.

> I think they call it LAAS if its at an airport.

No, LAAS is a completely different thing, where the correction comes
from local ("L") stations, not from a satellite covering a wide ("W")
area.


--
Thomas Borchert (EDDH)

Peter R. wrote:
> Dave Butler > wrote:
>
wrote:
>>
>>>I have the ear of some local government development people, who are
>>>contemplating upgrading some airports. Money is tight, so an ILS is
>>>probably not under consideration. So, I want to recommend to them
>>>checking into a WAAS installation. Does anyone know what the prices of
>>>such equipment for an airport are, which companies are selling them,
>>>and how much it costs to get the FAA to then create a WAAS IFR
>>>approach?
>>
>>There's no ground equipment requirement, all the equipment is airborne.
>
> If the airport is not currently equipped for instrument landings, wouldn't
> it require approach lighting and proper runway markings?

Quite right, there may be some such requirements. I thought I had written
something like that, but looking back, I see I only mentioned possible obstacle
removal requirements (which you snipped). Can't you read my mind?

thank you, gentlemen. I must admit I am only training to be an IFR
pilot, so I am not really up to snuff.

actually, my goal is to convince the local authorities to turn one
airport into a "general aviation" heaven. interestingly enough, the
local authorities here have more interest in developing the airport
than do the actual operators. The operators are not focused on GA, but
on big airplane airports instead. (PS: I will also ask for hangar
space creation, and some other niceties.)

now, our airport already has IFR procedures (GPS, localizer, VOR), but
no ILS. I was hoping to talk the decision-makers into a not-too-high
cost solution that takes advantage of the GPS/WAAS capabilities that
virtually all GPS's now seem to have built-in, so that we can institute
better IFR approaches with more accuracy and lower decision heights.

who are the vendors of LAAS? (I presume any WAAS capable GPS can also
take advantage of LAAS---right?) what are the cost factors of LAAS?

/iaw

> who are the vendors of LAAS? (I presume any WAAS capable GPS can also
> take advantage of LAAS---right?) what are the cost factors of LAAS?
>

LAAS is nowhere near certification. LAAS approaches are not available.
You'll need a ground station broadcasting GPS correction signals in the
vicinity of the airports. But I wonder what you would need it for if you
get something almost as good as an ILS with WAAS.

--
Thomas Borchert (EDDH)

wrote:
> thank you, gentlemen. I must admit I am only training to be an IFR
> pilot, so I am not really up to snuff.
>
> actually, my goal is to convince the local authorities to turn one
> airport into a "general aviation" heaven. interestingly enough, the
> local authorities here have more interest in developing the airport
> than do the actual operators. The operators are not focused on GA, but
> on big airplane airports instead. (PS: I will also ask for hangar
> space creation, and some other niceties.)
>
> now, our airport already has IFR procedures (GPS, localizer, VOR), but
> no ILS. I was hoping to talk the decision-makers into a not-too-high
> cost solution that takes advantage of the GPS/WAAS capabilities that
> virtually all GPS's now seem to have built-in, so that we can institute
> better IFR approaches with more accuracy and lower decision heights.
>
> who are the vendors of LAAS? (I presume any WAAS capable GPS can also
> take advantage of LAAS---right?) what are the cost factors of LAAS?

Oh, so you already have a localizer approach. It's very likely that when your
WAAS approach is commissioned, the minimums will not be as good as the localizer
minimums.

AFAIK there are currently no publicly available LAAs approaches. Here's some
info on LAAS, including estimated costs, but I have no idea how old that
information is. http://gps.faa.gov/FAQ/index.htm I wouldn't hold my breath
waiting for LAAS.

With the limited information you've provided, my gut feel is you'll get more
bang for your efforts by concentrating on the FBO and hangar infrastructure.
WAAS/LAAS (at least today) are not going to give you very much capability that
you don't already have with the existing array of approaches.

DGB

http://www.avweb.com/newswire/10_18a/leadnews/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

> wrote in message
ups.com...
>
> thank you, gentlemen. I must admit I am only training to be an IFR
> pilot, so I am not really up to snuff.
>
> actually, my goal is to convince the local authorities to turn one
> airport into a "general aviation" heaven. interestingly enough, the
> local authorities here have more interest in developing the airport
> than do the actual operators. The operators are not focused on GA, but
> on big airplane airports instead. (PS: I will also ask for hangar
> space creation, and some other niceties.)
>
> now, our airport already has IFR procedures (GPS, localizer, VOR), but
> no ILS. I was hoping to talk the decision-makers into a not-too-high
> cost solution that takes advantage of the GPS/WAAS capabilities that
> virtually all GPS's now seem to have built-in, so that we can institute
> better IFR approaches with more accuracy and lower decision heights.
>
> who are the vendors of LAAS? (I presume any WAAS capable GPS can also
> take advantage of LAAS---right?) what are the cost factors of LAAS?
>
> /iaw
>

An important part of the precision approach environment is the airport
surface itself: an adequate runway clear zone and adequate approach
lighting. Just because you can get a WAAS signal does not mean a
particular runway is going to be appropriate for a 200 ft minimum.

Dave

wrote:
> I have the ear of some local government development people, who are
> contemplating upgrading some airports. Money is tight, so an ILS is
> probably not under consideration. So, I want to recommend to them
> checking into a WAAS installation. Does anyone know what the prices of
> such equipment for an airport are, which companies are selling them,
> and how much it costs to get the FAA to then create a WAAS IFR
> approach?
>
> Sincerely,
>
> /iaw
>

Dave S wrote:

> An important part of the precision approach environment is the airport
> surface itself: an adequate runway clear zone and adequate approach
> lighting. Just because you can get a WAAS signal does not mean a
> particular runway is going to be appropriate for a 200 ft minimum.

For whatever it's worth, the runway markings, taxiway spacing, and obstacle
clearance areas are what make for a 200-foot Decision Altitude (DA).
Approach lights (ALS) are for visibility credit. With everything else
satisfied but no ALS the DA will still be 200 feet, with a visibility of
3/4. Add ALS to that environment and it becomes 200 and 1/2.

Now this I find interesting.

I understand obstacle clearance, but had no idea that runway markings
and taxiway spacing affects DA.

I can understand runway markings (although I thought they were
standard for precision approaches) but taxiway spacing?

Porque?




On Wed, 16 Feb 2005 05:06:50 -0800, wrote:

>
>
>Dave S wrote:
>
>> An important part of the precision approach environment is the airport
>> surface itself: an adequate runway clear zone and adequate approach
>> lighting. Just because you can get a WAAS signal does not mean a
>> particular runway is going to be appropriate for a 200 ft minimum.
>
>For whatever it's worth, the runway markings, taxiway spacing, and obstacle
>clearance areas are what make for a 200-foot Decision Altitude (DA).
>Approach lights (ALS) are for visibility credit. With everything else
>satisfied but no ALS the DA will still be 200 feet, with a visibility of
>3/4. Add ALS to that environment and it becomes 200 and 1/2.

>> An important part of the precision approach environment is the airport
>> surface itself: an adequate runway clear zone and adequate approach
>> lighting. Just because you can get a WAAS signal does not mean a
>> particular runway is going to be appropriate for a 200 ft minimum.
>
> For whatever it's worth, the runway markings, taxiway spacing, and obstacle
> clearance areas are what make for a 200-foot Decision Altitude (DA).
> Approach lights (ALS) are for visibility credit. With everything else
> satisfied but no ALS the DA will still be 200 feet, with a visibility of
> 3/4. Add ALS to that environment and it becomes 200 and 1/2.

For now, the lowest possible DA for WAAS approaches (LPV minima) is 250 feet.
Getting down to 200 feet (GLS minima) will require major system changes,
probably including a second civil GPS frequency, and will not happen before
2013 at the earliest.

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"?

:-(

/iaw


Bob Gardner wrote:
> http://www.avweb.com/newswire/10_18a/leadnews/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
>

wrote in news:1108602143.346760.33310
@l41g2000cwc.googlegroups.com:

> 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"?

Approaches that use WAAS have been commissioned all over the US. IFR-
certified units that use WAAS are still rather rare, IME. WAAS doesn't
work with non-WAAS GPS units, so the aircraft has to be fitted with new
equipment, and it just isn't economically viable for most pilots.

But there is no need for a precision GPS approach at most airports. A
standard GPS approach works most of the time.

--
Regards,

Stan

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

Bob Gardner wrote:
> http://www.avweb.com/newswire/10_18a/leadnews/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. 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

Personal web site: http:/www.moorecad.com/scott
My electronics engineering consulting site: http://www.moorecad.com
ISO 7185 Standard Pascal web site: http://www.moorecad.com/standardpascal
Classic Basic Games web site: http://www.moorecad.com/classicbasic
The IP Pascal web site, a high performance, highly portable ISO 7185 Pascal
compiler system: http://www.moorecad.com/ippas

Good does not always win. But good is more patient.

wrote:

> I have the ear of some local government development people, who are
> contemplating upgrading some airports. Money is tight, so an ILS is
> probably not under consideration. So, I want to recommend to them
> checking into a WAAS installation. Does anyone know what the prices of
> such equipment for an airport are, which companies are selling them,
> and how much it costs to get the FAA to then create a WAAS IFR
> approach?
>
> Sincerely,
>
> /iaw
>

As the AOPA has stated, WAAS will first be used to offer controlled
descent on standard approaches, an alternative to "dive and drive"
stepdowns, which makes it completely legal. There is no requirement
for HOW you get down to the runway, just as log as you observe minimums,
which means a likely mention in the AIM that you are supposed to keep
an eye on your standard altimeter.

I don't think the outlook for WAAS aproaches is rosy. What will happen
is WAAS approaches that have minimums just as bad as the normal GPS
approaches. To get more would require new lighting, runway marking,
and FAA surveys. And recall that the FAA does not just survey the
runway once, they have to do it regularly, with an expensive monitoring
aircraft. Runway markings are not a trivial subject. A lot of fields
have runways so bad they would have to get resurfaced just to be
properly painted.

I think it will happen, but the AOPA seems to be spreading this idea
that we will get 250 minimums overnight. This is going to be a long
process.

--
Samiam is Scott A. Moore

Personal web site: http:/www.moorecad.com/scott
My electronics engineering consulting site: http://www.moorecad.com
ISO 7185 Standard Pascal web site: http://www.moorecad.com/standardpascal
Classic Basic Games web site: http://www.moorecad.com/classicbasic
The IP Pascal web site, a high performance, highly portable ISO 7185 Pascal
compiler system: http://www.moorecad.com/ippas

Good does not always win. But good is more patient.

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)

"Ron Rosenfeld" > wrote in message
...
> 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

>>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.

Eclipsme wrote:
> "Ron Rosenfeld" > wrote in message
> ...
> > 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

wrote:

> Now this I find interesting.
>
> I understand obstacle clearance, but had no idea that runway markings
> and taxiway spacing affects DA.
>
> I can understand runway markings (although I thought they were
> standard for precision approaches) but taxiway spacing?
>

Yes. It's an Airports standard, not a TERPs criteria. It's contained in the
airport design advisory circular.

The rationale is spacing for wingtips in low visibility for spacing. And, there
is the issue of avoiding back-taxi at Class E or G airports.

wrote:

> I still don't get it.
>
> What does descending to 250 ft vs 200 ft on an approach have to do
> with wingtip spacing or back-taxi operations?
>

I believe wingtip spacing has to do with the lowest visibility that can be
authorized. One location I am familiar with is KCRQ where the ILS vis was increased
from 2400 to 4000 because the taxiway was too close for Dash 8 aircraft to use at RVR
2400.

I do not have experience with how the airport design folks think. If you want to
know more, I recommend you look at the airport ACs.

As to back-taxi, I guess it becomes an issue of having sufficient visibility to see
and avoid the aircraft on the runway coming at you.

wrote:

> Well, I can understand where the visibility requirement would be
> affected, but I don't see why DA would change because of taxiway
> spacing.

I am not sure it would affect DA. It didn't at KCRQ.

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)

"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
> > ...
> > > 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/leadnews/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.