WAAS is to GPS what the assembly line was to cars -- they
both turned a good product into a fantastic one
By ANN Senior Correspondent Kevin O'Brien
If 2004 was the year of the glass panel, 2005 is
shaping up to become the year of a little-known acronym: WAAS.
Does it rhyme with "gas" or with "boss?" Or is it sounded out
letter-by-letter, like the call sign of an AM station east of the
Mississippi, W-A-A-S? Beats me with a stick, I've heard all those
pronunciations -- and I'm going to be hearing them more and more,
and so are you. What it really stands for is "Wide Area
Augmentation System," an invention of the Stanford University GPS
Lab that has turned the ubiquitous GPS into a marvel of navigation
with unparalleled accuracy.
This is GPS-dependent technology, so for all you airline pilots
hunkered down behind steam gages wondering whether you will still
have even those to look at after the next round of furloughs,
sorry. This is, for now, GA technology, and what
technology it is! From the viewpoint of
aviation, WAAS creates the possibility to overlay a
precision approach on any runway or helipad, for the rotary
motivated.
Why WAAS Is Needed
The FAA has limited the uses for which it approves GPS. That's
because GPS alone does not meet the FAA's requirements for the
precision and reliability of other navigationa
technology. WAAS, in a nutshell, provides a way to correct for
errors in the GPS signal, regardless of which of a plethora of
technical problems is responsible for the error. As importantly, a
WAAS-enabled receiver gets information about whether a satellite's
information is reliable or not -- a sort of high-tech
self-check.
WAAS can provide localizer-type non-precision approaches where
there is no localizer -- Lateral Navigation or LNAV. It can
provide ILS type vertical guidance, using the same glideslope
indicator your ILS uses -- Vertical Navigation, VNAV, which gives
you as low as a 350-foot above-terrain minimum descent altitude. It
can also provide guidance for high precision approaches --
Localizer Performance w/Vertical or LPV -- that yields as low
as 250 foot MDAs, and keeps you within one meter of the
glideslope horizontally and vertically.
WAAS is also useful for enroute navigation. When GPS
first got underway, in the bad old days of Selective Availability,
a deliberate degrading of the signal for military reasons, you were
doing alright to be pinpointed within 100 meters. Now you're down
to one. WAAS may prove to be beneficial to controllers on the
congested Oceanic routes, where there is no surveillance radar.
Right now they have to give up a large bloc of
airspace to each aircraft, which reports its position by
long-range HF radio -- when HF is working. That airspace has the
imprecision of INS, even when factoring LORAN and other
means of oceanic navigation.
How Does It Work?
On top of the basic GPS
system, WAAS adds a couple dozen ground reference stations across
the USA. These reference stations listen to the GPS satellites and
pass the data to east and west coast master stations in
Herndon (VA) and San Diego (CA), respectively. The master station
then constructs a message that encodes a correction for all the
cumulative data errors in the GPS signals. The stations, of course,
know exactly where on Earth they are, given that they are firmly
nailed into the ground.
The beauty of the system is that the master stations do
not try to distribute their information from antenna
towers to end-user receivers. Instead, they uplink the data to two
special satellites in geosynchronous orbit 22,300 miles over the
equator -- one over the Atlantic Ocean, the other over
the Pacific Ocean.
Those satellites then broadcast the information so that any
WAAS-aware GPS receiver can exploit it immediately. At any given
time, one of the master stations operates. Every four hours
they hand off duties, completely transparently from a user's point
of view. Should a disaster knock one station off line, the other
takes over automagically, and can run the system until its partner
returns.
WAAS differs from Differential GPS, which is used by surveyors,
in that it does not require any special receiving equipment
or any local ground stations.
You Can Buy It Now
The TSOs for WAAS receivers (C146a) and antennas (C145a) have
been stable for a while, and the vendors are all over them. Garmin,
for example, will sell you a WAAS-enabled receiver right now
-- it has a whole line of them. The current comprehensive IFR
Navigation System with WAAS is the GNS-480, which is one of the
things the GPS powerhouse acquired (as the CNX 80) when they bought
UPS Aviation Technologies. If you have an older Garmin system,
like the 430 or 530, or the G1000 glass panel, you'll have access
to an upgrade sometime in 2005. Users of older UPS AT Apollo
navigation systems may not be left out in the cold entirely: GX55,
GX65, GX50 and GX 60 systems can be traded in to take the edge
off the GNS-480's hefty $12,000 MSRP. You should shop around,
though, because the units can be had for as little as $8000 and
change, plus installation.
Likewise, the slick Chelton EFIS has been available with a
certified WAAS card for most of 2004. Chelton is in on the ground
floor by virtue of its participation in a test of this technology
in Alaska over the last couple of years. The Chelton EFIS offers
all the usual benefits of such a device, plus Highway-in-the-sky
(HITS) technology, and 3-D terrain and obstacle depiction, which
the company calls "Virtual VFR".
Other avionics firms are not far behind. A number of vendors of
high-end flight-management systems such as Honeywell use the
same certified card from FreeFlight Systems (formerly Trimble
Navigation) that Chelton relies on. This coming year is going to
see a slew of new product announcements and upgrades, so brace
yourself for the onslaught.
In all cases, approach-certified, TSO'd nav units will be
panel-mounted. You will be able to get handhelds that use WAAS for
greater accuracy, but no handheld will ever be certified for
approaches, says the FAA.
But, who knows what's down the road? When GPS was opened to
civilians at the end of 1993, if you said that someday you would be
able to fly an ILS-like approach into a runway that doesn't even
have a localizer, you'd have been ushered into a quiet corner of
the pilots' lounge, where you couldn't corrupt the student pilots,
and gently restrained until the men in the clean white coats
came for you. As recently as 2000, WAAS itself was on the chopping
block, with the aviation-savvy Congressman John Mica (R-FL) calling
it a "$4 Billion boondoggle."
What Parts of the Puzzle Are Missing?
Right now, WAAS is US-centric technology that works in the
United States and contiguous territories and waters. Canadians will
probably benefit right away, especially if Transport Canada gets
motivated and designs some approaches.
Europe and Japan are working on disparate versions of this
technology. The avionics vendors say that they can make it work
together with WAAS, which probably matters the most to those who
make frequent intercontinental trips. Most everywhere in the
developed world will be covered by WAAS, or something similar,
within ten years.
Unfortunately,
that means that if you fly the unfriendly skies of
Central or South America, or the badlands of Africa, where you
might benefit the most from this type of technological improvement,
you are going to be disappointed.
At press time, there are only some 500 published
approaches for some 200 US airports -- depending on who you
ask. The FAA numbers are confusing, because they've thrown the old
GPS approaches in with the new ones that WAAS made possible.
In the category that's most novel, and most useful to GA -- LPV
approaches at non-Part 139 (i.e. non-airline) airports
-- there are a whopping twelve approaches at present,
most of them close to the nation's capital... or at least within
range of Phil Boyer's 172 at FDK -- home to one of the 12. But some
of these fields, like Frankfort (KY) or Westminster (MD) had no
prior precision approach. Many of the Part 139 certified
airports that are getting these approaches are not the huge Class B
wide-body farms -- they're places like Tallahassee (FL), which now
sports four such approaches to 250-300 feet above terrain, and
which previously had just one ILS.
You Don't Even Have To Have a Plane
While the advantage of a precision approach everywhere is
unlikely to excite those who will never make a precision approach
anywhere, the accuracy that WAAS provides will
benefit all GPS applications -- if the GPS is
WAAS-enabled. This means that your auto's navigation system may not
show you disconcertingly motoring alongside the streets
and you can take your dive boat back to the place you like
every time. WAAS increases the power and utility of GPS technology,
which has already revolutionized all kinds of location-dependent
activities. Like any revolution, your life will be changed by it,
whether you personally join in or not.