National Airspace System: Status of Wide Area Augmentation System Project

In the 1980s, FAA began considering how a satellite-based navigation system might eventually replace the ground-based system that has long provided navigation guidance to aircraft. In August 1995, after several years of research, FAA contracted with Wilcox Electric to develop WAAS to enhance GPS. However, because of concerns about the contractors work, FAA terminated the contract in April 1996. In May 1996, the agency entered into an interim contract with Hughes Aircraft Company (now Raytheon Systems), with the contract becoming final in October 1996. Accuracy, integrity, availability, continuity, and service volume are the major performance goals for the system to meet. Accuracy is defined as the degree to which an aircrafts position as calculated using the system conforms to its true position. For precision approaches to runways, WAAS is expected to provide aircraft operators with position accuracy within 7.6 meters 95 percent of the time. Integrity is the systems ability to provide timely warnings when its signals are providing erroneous information and, thus, should not be used for navigation. WAAS is expected to provide a warning to aircraft operators within 5.2 seconds. Availability is the probability that, at any given time, the system will meet FAAs accuracy and integrity requirements for a specific phase of flight. For precision approaches, WAAS is expected to be available all but 9 hours per year. Continuity is the probability that the systems signal will meet accuracy and integrity requirements continuously for a specified period. Service volume is the area of coverage for which the systems signal will meet availability requirements.