Wide Area Augmentation System

Wide Area Augmentation System. It is a satellite-based augmentation system developed by the Federal Aviation Administration to augment the Global Positioning System, providing enhanced integrity, accuracy, and availability for aviation navigation. The system broadcasts correction and integrity data via geostationary satellites, enabling precision approaches at thousands of airports across North America. Its implementation marked a significant advancement in the National Airspace System, supporting operations from en-route navigation to Category I approaches.

Overview

The primary purpose is to improve the performance of GPS signals for critical navigation, particularly within the demanding environment of civil aviation. It was commissioned by the FAA to meet stringent requirements for safety and reliability, effectively creating a more robust navigation aid. The service area primarily covers the continental United States, Alaska, Hawaii, and portions of Canada and Mexico. This coverage supports a wide range of aircraft, from general aviation to commercial airliners operating for carriers like American Airlines and United Airlines.

Technical description

The infrastructure consists of a network of precisely surveyed ground reference stations located across its service area. These stations continuously monitor signals from GPS satellites and relay data to master stations, such as those operated by the Raytheon Company. The master stations process this information to generate differential corrections and integrity messages, which are then uplinked to Inmarsat and Intelsat geostationary satellites. These satellites broadcast the correction signal on the same L1 frequency as GPS, which is received by avionics like the Garmin GNS 430. The system corrects for errors caused by ionospheric delay, satellite clock drift, and orbital inaccuracies.

Development and implementation

Development was initiated by the FAA in the 1990s, with key contracts awarded to industry leaders including Honeywell and Lockheed Martin. The system underwent extensive testing, including trials at facilities like the William J. Hughes Technical Center. It was declared operational for safety-of-life navigation in 2003, following approval from bodies like the Radio Technical Commission for Aeronautics. Implementation required the certification of new avionics standards and the integration of its signal into the existing National Airspace System, a process overseen by the Department of Transportation.

Performance and accuracy

It provides a high level of service, typically offering accuracy better than 1.0 meter vertically and 1.5 meters horizontally. This performance meets the requirements for precision approach operations, as defined by standards from the International Civil Aviation Organization. The integrity function alerts users within 6.2 seconds if the system should not be used for navigation, a critical feature for approaches in conditions like those at San Francisco International Airport. Availability exceeds 99.9% throughout the service area, ensuring consistent reliability for air traffic control procedures.

Applications and users

The primary application is in aviation, enabling Localizer Performance with Vertical guidance and Category I instrument approach procedures at airports without expensive ground-based infrastructure like Instrument Landing System. It is widely used in general aviation aircraft equipped with modern glass cockpit systems from manufacturers like Cirrus Aircraft and Cessna. Beyond aviation, the signal is also utilized in agriculture for precision farming, surveying by organizations like the United States Geological Survey, and various maritime navigation systems. The United States Coast Guard employs it for certain navigation aids.

Future developments and alternatives

Future evolution is tied to the modernization of GPS, including the utilization of the new L5 frequency to provide more robust dual-frequency service. This upgrade is part of broader programs like the FAA's Next Generation Air Transportation System. Internationally, similar systems exist, such as the European Geostationary Navigation Overlay Service in Europe, Multi-functional Satellite Augmentation System in Japan, and the GPS Aided Geo Augmented Navigation system in India. Research into advanced air traffic management concepts, including those for urban air mobility, continues to rely on the foundational capabilities provided by this and other satellite navigation systems. Category:Aviation in the United States Category:Global Positioning System Category:Radio navigation