WAAS charts new course in air navigation history

 - August 4, 2008, 6:54 AM

The FAA flipped the switch on its wide-area augmentation system (WAAS) at 12:01 a.m. on July 10, potentially opening up thousands of runways at 5,400 public-use airports for near-precision approaches in both lateral and vertical guidance modes.

Some 500 approaches to more than 200 airports have already been charted, and as soon as the avionics are certified, properly equipped aircraft will be able to shoot GPS approaches down to 350 feet and one-mile visibility. Two manufacturers already have IFR-certified WAAS receivers for the Lnav mode and expect to have certification for vertical navigation within several months.

But FAA Administrator Marion Blakey said the official commissioning of WAAS marks only the first step in what has been an arduous, long and expensive process that will eventually be refined to provide ILS-like precision approaches. While general aviation will likely be the biggest beneficiary, many Part 121 regional airlines are expected to equip their turboprops and regional jets with WAAS approach capability because they often fly into airports that lack instrument approaches with vertical guidance.

Charlie Keegan, FAA associate administrator for research and acquisitions, promised that “it gets better and better and better.” With the addition of new geostationary satellites and strategically placed ground-reference stations, WAAS coverage will be enlarged from the current approximately 90 percent of the continental U.S. to blanket all of the lower 48 and most of Alaska.

By the end of the year, more accurate LPV (localizer precision with vertical guidance) approaches, combined with TERPS optimization, will allow descent minimums as low as 250 feet. WAAS accuracy is within one to 1.5 meters (compared with seven to 10 meters without an augmented signal) and signal availability is 99.999 percent. “That is great precision and we are very pleased with it,” said Blakey.

With WAAS, signals from GPS satellites are received by precisely surveyed ground-reference stations, and any errors in the signals are identified. Each station in the network relays the data to one of two wide-area master stations, where correction information for specific geographical areas is computed. A correction message is prepared and uplinked to a geostationary communications satellite via a ground uplink station. This correction is broadcast on the same frequency as GPS.

LPV approaches are being introduced into the National Airspace System (NAS) along with WAAS to complement less precise Lnav/Vnav approaches. Not only will new LPV procedures be developed, according to the FAA, but virtually all of the existing GPS-Rnav procedures will be upgraded to include LPV approach minimums. WAAS will ultimately be able to support Cat I precision approaches once the second civil broadcast frequency is added to the GPS constellation, the agency said.

Conceding that WAAS “took longer and cost more money than we all thought,” Blakey suggested it actually is an example of the oft-cited “rocket science” sobriquet because “we’re doing things that have never been done before.” One of the biggest challenges was correcting the GPS signals that are distorted by the ionosphere. She said scientists came up with a special software program that continuously tested the integrity of the WAAS system.

WAAS is monitored 24/7 from two operations and maintenance stations–the Pacific Operations and Control Center in San Diego and the other at the National Operations and Control Center, collocated with the FAA Air Traffic Control Systems Command Center near Washington Dulles International Airport.

All of this isn’t coming cheap, and FAA personnel tossed around various figures during a press briefing on the official first day of WAAS usage. The agency is now putting the “baseline” total life-cycle cost (out to 2020) at $3.2 billion. That includes the initial development cost of $790 million beginning in 1994, as well as the cost of acquiring geostationary satellites.

Only two GA avionics manufacturers–Chelton Flight Systems and United Parcel Service Aviation Technology–are marketing WAAS receivers, and they are currently certified only for lateral guidance. Vertical navigation capability will be added through datacards without removing the unit from the aircraft. Although the avionics boxes now on the market integrate many functions, the cost for a standalone WAAS receiver is estimated to be in the $8,000 range. Prices are expected to drop as other avionics manufacturers ramp up production within the next six months.

While a typical ILS costs about $1.5 million per runway end, Keegan stressed that this “really does open up the end of every single runway to a near-precision approach capability across the country.” He said the FAA is charting 300 procedures a year, using computer modeling to establish those approaches. However, even at that nearly one-a-day rate, it would take more than 30 years just to do two runway ends at the 5,400 GA airports.

Recalling the long and checkered history of WAAS, AOPA president Phil Boyer said there are those in Congress who never saw WAAS for its benefit. “There are those in the outside world–even some of the airlines–who said, ‘Well, it’s a long way away,’” he said. “Yet now they’re beginning to realize that after WAAS there will be another acronym–LAAS [local-area augmentation system].”

Blakey said the groundwork was laid back in the 1980s when President Reagan opened up the GPS constellation to civilian use. Along the way, one WAAS contractor was replaced by another, and as late as 2000 some members of Congress were calling it a $4 billion boondoggle.

But after an independent review panel of experts found that WAAS could deliver Lnav and Vnav services, a summit meeting among top-level FAA officials and WAAS contractors, as well as industry, airline and GA user groups, agreed that the program should be continued.

“Now that the FAA has turned on the signal, the agency has to accelerate charting new approaches at those airports that don’t have them now,” he said. “The FAA must take innovative steps, such as turning to the private-sector survey, and design these approaches.” One of the first airports to receive an LPV approach will be Leesburg Executive Airport, Va.

Although WAAS is authorized for use only within the NAS, the FAA said that it is capable of providing service sufficient for Lnav/Vnav and LPV approaches across large portions of Canada and Mexico with the addition of minimal ground-reference stations in those countries.