The Wide Area Augmentation System (WAAS) is a navigational system representing an enormous leap forward in air navigation. By virtue of its extensive coverage area, WAAS provides vertically-guided approach capability at thousands of airports and airstrips where this capability had previously not been affordable. It is a core element in transitioning to the satellite-based air traffic control system of the future.
WAAS is designed to improve the accuracy and ensure the integrity of positioning and timing information from Global Positioning System (GPS) satellites.
- GPS alone does not meet FAA’s navigation requirements for accuracy, integrity and availability for all operations; nor does GPS provide the necessary guarantees that its signal will be accurate, available, and safe to use at all times.
- WAAS corrects for the GPS satellite position errors, ionosphere delays, and other disturbances in the GPS signals, improving the accuracy and reliability of the users’ position solution.
- More importantly, WAAS warns the pilot when the satellites are not functioning correctly and should not be used for navigation.
Although the WAAS was designed for aviation users, it supports a wide variety of non-aviation uses including agriculture, surveying, recreation, and surface transportation–just to name a few. The WAAS signal has been available for non safety-of-life applications since August 2000, and numerous manufacturers have developed WAAS-enabled GPS receivers for the consumer market. Today, there are millions of non-aviation WAAS-enabled GPS receivers in use.
WAAS was developed for the FAA by Raytheon Corporation.
How WAAS Works
WAAS uses a network of precisely-located ground reference stations that monitor GPS satellite signals. These stations are located throughout the continental U.S., Hawaii, Puerto Rico, Alaska, Canada and Mexico. The stations collect and process GPS information and send the information to WAAS master stations. The WAAS master stations develop a WAAS correction message that is sent to user receivers via navigation transponders on geostationary satellites. The WAAS message improves the accuracy, availability, and safety of GPS-derived position information. Using WAAS, GPS signal accuracy is improved from 20 meters to approximately 1.5 – 2 meters in both the horizontal and vertical dimensions. WAAS hardware consists of: 38 ground reference stations, 2 master stations, 2 geosynchronous satellites, 4 uplink stations, 2 operational control centers, and the WAAS terrestrial communications network.
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