The Federal Aviation Administration (FAA) is transitioning from a system of ground-based navigation aids to one based upon a satellite-based Global Positioning System (GPS). Radar and other ground-based navaids limit the amount of airspace available and can increase travel distance, since aircraft must follow one navigational fix to another. Under GPS, several sequenced satellites orbiting the earth each transit an omnidirectional signal that reaches a receiver on the aircraft, which with precise timing information calculates a radius of distance from each satellite. The intersection of at least three spherical surfaces allows for the automated calculation of the aircraft's position. This process provides highly accurate information for en route navigation. GPS is already being used for navigation in oceanic and en route airspace.
In order to enhance the accuracy and reliability of GPS so that it can be used as a primary means of navigation and nonprecision approaches, the FAA has been augmenting the system with a nationwide network of reference stations that will receive and refine signals from the GPS satellites. Known as the Wide Area Augmentation System (WAAS), these enhancements will allow so-called "differential" GPS to be used as a primary means of navigation for en route travel and nonprecision approaches in the United States, as well as near-precision approaches. WAAS will also allow a pilot to determine a horizontal and vertical position within 6 to 7 meters, compared with the 100-meter accuracy available today from the basic GPS service. The FAA is also testing other applications of GPS, such as Automatic Dependent Surveillance-Broadcast (ADS-B) as part of its transition from central control to "Free Flight" concepts. The aim of Free Flight is to give pi ...