ATM Modernization

WAAS-Capable GPS Receivers

By David Jensen | September 1, 2003
Send Feedback

Now that the Federal Aviation Administration (FAA) has commissioned its wide area augmentation system (WAAS), GPS navigation will offer a level of integrity supporting precision approaches. Already two avionics manufacturers have placed WAAS-capable systems on the market. Other manufacturers plan to do the same.

FAA Administrator Marion Blakey described July 10, when WAAS was commissioned, as "a banner day." It also clearly was a day of relief for the agency, which has seen the program mushroom far beyond its original budget and timetable. The U.S. Department of Transportation inspector general set the WAAS program’s total costs at $3.2 billion, but FAA officials stress that the figure represents WAAS’ development cost and life-cycle cost through 2020. They quote the WAAS program’s total cost at $1.9 billion, including $791 million for development costs. The issue of system integrity caused the WAAS program’s about three-year delay. "We had difficulties in ’99," says Charles Keegan, FAA’s associate administrator for research and acquisitions. He credits the government/industry WAAS integrity panel (WIP) for finally resolving those difficulties.

Since commissioning WAAS, FAA has been phasing in system capability. In July WAAS began providing lateral navigation (LNAV) for non-precision instrument approaches. LNAV combined with vertical navigation (VNAV) was to be the second phase, allowing instrument approaches down to a 350-foot decision level. And by this month, WAAS was scheduled to provide LPV (localizer performance approaches with vertical guidance) capability (phase three), which, with a 250-foot decision height, is comparable to achieving Category I precision approaches.

To use WAAS, aircraft operators must have a WAAS/GPS sensor approved to TSO (technical standard order) 145a and a navigation system approved to TSO 146a. The airports they fly to under instrument flight rules (IFR) must have WAAS approaches designed, checked, approved and published. Keegan says FAA plans to have 300 airports approved for WAAS approaches per year, "or about one a day."� In mid-July, FAA claimed it had about 500 WAAS approaches certified at 200 airports. Avionics manufacturers planning WAAS-capable systems no doubt are calculating how many approved airports are needed to advantageously time the introduction of their new products.

WAAS coverage requires geostationary communications satellites to relay corrections to the GPS signal. Two satellites–one over the Pacific Ocean and one over the Atlantic–serve North America. However, the L-band downlink signal from the satellites can be weak in parts of the United States, so FAA seeks "real estate" to house WAAS transponders in two geostationary satellites (one for backup) positioned above the central United States. "We’ll be putting up satellites in the next few years," says Keegan.

Embracing the ILS systems installed at about 600 airports (many of which are major hubs) in the United States, the air transport community initially has been fairly indifferent to WAAS availability. But the general aviation community finds the system promising, as WAAS can potentially provide precision approach capability at 5,400 or more airports. Small wonder then that Phil Boyer, president of the Aircraft Operators & Pilots Association (AOPA), joined Blakey and Keegan in enthusiastically announcing the WAAS commissioning to the media. "Now the people who make receivers will be encouraged to develop and produce WAAS-capable receivers," he noted. "A box [receiver] with vertical nav capability costs about $8,000, but I’m confident that [growth in] the market will bring the price down to $4,000."

Pilots in Alaska, where ground navigational aids are sparse, are benefiting from the use of WAAS for en-route navigation. Alaska’s mountains can block signals from ground navaids, unless pilots flying under instrument flight rules (IFR) operate at high altitudes. Even a short IFR flight might require operating at 14,000 feet. But FAA and Mitre Corp. have established satellite-based IFR routes in Alaska that allow instrument flight as low as about 5,000 feet.

FAA officials announced the WAAS commissioning at the National Operations and Control Center (NOCC) in Herndon, Va., where one of the two WAAS operations and maintenance stations–also called master stations–is located. The other station is located in San Diego. While one station controls WAAS, the other monitors the system, and the two stations switch duties every two hours. They are equipped with IBM RISC 3000s, which display system health status, including maintenance information and alarms. The WAAS system also includes a network of 25 reference stations with precisely positioned GPS receivers that detect errors in the GPS satellite signal. Corrections, relayed to the master stations, are then uplinked to the geostationary satellites, which often are called "bent pipes" because, like water through an elbow-shaped tube, they downlink the uplinked data to the airborne receiver. Corrections, which assure both vertical and horizontal accuracy down to about 3 feet (1 meter), are uplinked via C-band from ground stations in Clarksburg, Md., Santa Paula, Calif., and Brewster, Wash.

Two companies, Chelton Flight Systems and UPS Aviation Technologies (UPSAT), offer WAAS-capable receivers and are participants in the Capstone program. "Capstone broke the logjam," says Gordon Pratt, president of Chelton Flight Systems, commenting on the demand for WAAS receivers. The program enabled WAAS to be tested and used by a significant number of aircraft operators, he adds.

UPSAT’s WAAS sensor, which received FAA certification in autumn 2002, is incorporated in its CNX80 WAAS/GPS navigator, which also includes a color display, mapping feature, nav/com, localizer and glideslope. The WAAS receiver includes 15 channels and can process five position updates per second. The CNX80 received FAA certification in June.

Interestingly, Garmin International is in the process of acquiring UPSAT and has plans to incorporate a WAAS-capable receiver in its GNS 430 and GNS 530 integrated GPS/nav/com system with color moving map display. As this is written, Garmin officials could not comment on the integration of the two companies’ product lines. Peter Broumbaugh, a Garmin spokesman, says his company’s plans are to introduce the WAAS-capable GNS 430 and 530 by the fourth quarter of 2004. He adds that Garmin intends to have the WAAS upgrade available for the two GPS/nav/com systems, as well as for Garmin’s GPS 400 and GPS 500 navigation systems and the GNC 420 nav/com system, all with color displays.

Chelton claims it has the first WAAS-capable navigator. It was FAA-certified on March 27. The system marries the WAAS sensor from Waco, Texas-based FreeFlight Systems (previously Trimble Navigation) with Chelton’s electronic flight instrument system (EFIS), which includes, among other features, synthetic vision and highway-in-the-sky imagery.

FreeFlight Systems makes available both its 1201 TSO 145a-certified GPS/WAAS sensor and its 2101 navigation system, which already are installed in some 15,000 aircraft. According to Steve Williams, company president, the Model 2101, with TSO 129 (A1) approval, can be upgraded for WAAS capability. "The turnaround would be a couple of days, and the price for the upgrade would be about $2,500, including warranty, new face plate and reconditioning," he adds.

The 1201 and 2101 are options in Sandel Avionics’ and Honeywell’s terrain awareness warning systems, as well as in ACSS’ T2CAS ground and traffic warning system. Honeywell also has the 1201 sensor card in its HT 9100 flight management system. And, says Williams, FreeFlight will provide its GPS/WAAS sensor card for the Avidyne integrated flight deck package.

Rockwell Collins’ multimode receiver (MMR) includes a "high-integrity GPS" unit that supports both WAAS and the local area augmentation system (LAAS), and� the company is "developing software applications for both augmentation systems," according to a company spokesman. "We currently have MMRs in flight test which have both LAAS and WAAS implemented. The first TSO and certification of LAAS is planned for mid-2004," the spokesman adds. "The WAAS TSO and certification schedule will be consistent with airline/aircraft manufacturers’ requirements."

Likewise, CMC Electronics plans to have a WAAS receiver available by next year.

Receive the latest avionics news right to your inbox