2.5 Global Positioning System

The WAAS is a geographically broad augmentation to the basic Global Positioning System (GPS) service designed to improve the accuracy, integrity, and availability of the basic GPS service. Initial benefits will be provided by Phase I WAAS.

When Phase I is operational, WAAS will provide pilots with an en route through precision approach capability. En route through non-precision approaches will be available throughout the entire service area with an availability of 99.9 percent. Precision approach coverage will be provided in central regions of the continental United States (CONUS), serving approximately 50 percent of CONUS airports. Availability for precision approach is designed to be 95 percent.

Although WAAS offers the potential to replace Very-High-Frequency Omni-Directional Radar (VOR), Distance Measuring Equipment (DME), and Non-Directional Beacons (NDB) in the U.S., further enhancements are needed to the Phase I WAAS before this is possible.

The commissioning of Phase I WAAS for public use will take place in the Fall of 2000; however, in mid-1999 a signal capable of supporting non-safety applications, such as an aid to Visual Flight Rule (VFR) flight, became available.

Local Area Augmentation System (LAAS)
The other augmentation to the basic GPS service is the Local Area Augmentation System (LAAS). Similar to the WAAS concept, which incorporates the use of geostationary communication satellites to broadcast a correction message, the LAAS will broadcast its correction message via very high frequency (VHF) radio datalink from a ground-based transmitter.

The LAAS will meet the more stringent Category II/III requirements that exist at selected locations throughout the U.S. LAAS is intended to complement and function together with the WAAS, to supply users of the U.S. National Airspace System (NAS) with seamless, satellite-based navigation for all phases of flight. In practical terms, this means that at locations where the WAAS is unable to meet existing navigation and landing requirements (such as availability), the LAAS will be used to fulfill those requirements. In addition, beyond Category III, the LAAS will provide the user with a navigation signal that can be used as an all-weather surface navigation capability. This will enable the potential use of LAAS as a component of a surface navigation system and an input to surface surveillance/traffic management systems. It is fully expected that the end-state configuration will pinpoint the aircraft's position to within one meter or less, and do so at a significant improvement in service flexibility and user operating costs.

Additionally, both the WAAS and LAAS have the backing of aviation's main user groupsÐthe Air Transport Association (ATA) representing air carriers, and the Aircraft Owner's and Pilot's Association (AOPA) representing general aviation. These groups confirmed their support in an April 1998 press release which stated "the joint recommendations ask the Federal Aviation Administration to proceed with both wide-area and local-area augmentation systems for Global Positioning System (GPS) satellite navigation." Encouraged by these recommendations and the benefits that can be provided by WAAS and LAAS, the FAA remains strongly committed to these programs.

FAA POC:
Carl McCullough
202-493-4722