While the GPS wide-area augmentation system (WAAS) is likely to be commissioned for public use in July, the local-area augmentation system (LAAS) has fallen back by 12 months, with commissioning of the first installation now forecast in late 2005. This setback for LAAS was revealed to attendees at a December briefing given by FAA’s Satellite Operational Implementation Team (SOIT).

Both systems are designed to provide users with enhanced GPS accuracy and with fast alerting of satellite failures and/or system accuracy drift beyond tolerances. WAAS and LAAS are FAA-funded augmentations to the DOD’s GPS for en route/terminal and precision approach applications, respectively, to meet civil requirements for use in the NAS. The basic military GPS was not designed to provide either accuracy enhancement or prompt integrity failure warnings.

WAAS does this by using a widespread network of ground-monitoring stations across the NAS, each of which continuously tracks all GPS satellites above the local horizon and then sends its data to monitor centers on each coast of the U.S., where they are combined into a sort of error map of the country. This is then uplinked to two geostationary satellites, or GEOs, orbiting 24,000 mi above the equator–one over the eastern Pacific and one over the western Atlantic–and the GEOs in turn transmit this information to GPS airborne and surface users. The GEO data is transmitted over the civil GPS navigation frequency, in effect providing the users’ receivers with what it also sees as an additional GPS satellite.

LAAS Future Cloudy
But while WAAS and LAAS have been in development for several years, and have experienced both cost increases and program delays, the major problem with WAAS has been in proving the concept technically. LAAS, on the other hand, was shown fairly early in its development to work quite effectively as a landing guidance concept, but was hampered by resolving integrity issues and, perhaps equally important, questions of user need and acceptance. Both of these issues are now clouding LAAS’ future.

This is one of the two problems the FAA faces in pursuing the LAAS program, the other being that of user acceptance when the agency’s systems are fielded in 2005. As a result, the award of a LAAS development contract planned for September last year has been postponed until April or later. Bidders have been advised that when the contract is awarded, its first phase will call for intensive analyses demonstrating that the required integrity level will be met before production will be allowed to proceed. A contract “exit strategy” is also being formulated within the FAA should these demonstrations fail.

The WAAS program, while now seemingly “safe,” suffered a five-year delay due to integrity and other problems, resulting in a budget that swelled from $890 million to more than $3 billion. New FAA Administrator Marion Blakey is reported to have vowed not to have the same happen with LAAS during her watch, particularly as there is growing evidence that airline industry interest in Cat I LAAS is lukewarm at best, with interest expressed only in Cat II and III. The Catch-22 is, unfortunately, that Cat I is a necessary stepping-stone to the even more demanding Cat II and III, which were described by an FAA official as posing “large challenges.”

The avionics industry also faces challenges. While the need for GPS LAAS approach receivers is several years away, there would be a need for WAAS-compatible units by July, if the FAA’s forecast commissioning occurs at that time. For WAAS, a new receiver meeting the TSO C-146 specification, or an FMS WAAS sensor meeting TSO C-145, will be required. Some manufacturers have also stated that they will supply software upgrade kits to certain models of their current TSO C-129 units.

However, companies are unwilling to commit to avionics production yet, having a “once bitten, twice shy” caution about FAA predictions of WAAS readiness, following the earlier two-year delay. Consequently, price and delivery quotations are
not readily available, although this is expected to be eased as the manufacturers’ confidence levels grow. At the FAA SOIT meeting, avionics company representatives were noticeably quiet.