Wide Area Augmentation System

The Wide Area Augmentation System is a satellite-based augmentation system developed by the United States Federal Aviation Administration to improve the accuracy, integrity and availability of the Global Positioning System. It lets aircraft rely on GPS through every phase of flight, including approaches with vertical guidance, using a network of ground reference stations across North America and Hawaii that measure small variations in GPS satellite signals. Those measurements are relayed to master stations, which compute correction messages and send them to geostationary WAAS satellites for broadcast back to Earth, where WAAS enabled receivers apply the corrections to improve positioning accuracy. The International Civil Aviation Organization classifies WAAS as a satellite-based augmentation system, a category that also includes Europe's EGNOS, Japan's MSAS, India's GAGAN and Russia's SDCM.