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.

FMI: http://waas.stanford.edu