WIDE AREA AUGMENTATION SYSTEM (WAAS)

摘要

Global Positioning System (GPS) navigation signals alone are not adequate to support aviation navigation. GPS accuracy is acceptable for all but precision approach applications, but integrity, continuity, and availability are lacking. Wide Area Augmentation System (WAAS) hardware has been installed and used for testing since last summer. Wide Area Reference Stations receive GPS signals and forward them to Wide Area Master Stations for corrections processing. Augmentation messages are sent to the Ground Uplink Stations for transmission to Geosynchronous (GEO) satellites that retransmit the messages to avionics receivers in aircraft. WAAS is a safety critical system, meaning time to alarm is critical and transmission of hazardously misleading information is not allowed. Phase 1 WAAS will be commissioned in September of next year and will provide enroute through non-precision approach services throughout the US Flight Information Region. Precision approach services will be provided over roughly 50% of the continental US. END-state WAAS will provide CAT-1 precision approach navigation service throughout the continental US. The key to all WAAS operations is time. The GPS satellites, the GEO satellites, and all WAAS hardware suites must agree upon time. Precision time has been identified as one of the major untapped byproducts of WAAS.