The US Federal Aviation Administration (FAA) has delayed initial fielding of the Raytheon Wide Area Augmentation System (WAAS) by at least 14 months because of software development problems.

The WAAS was to have entered service in July 1999, but the FAA says this has been pushed back to September 2000 because it needs more time to complete development of a software safety package.

The system comprises a network of 35 ground reference stations that receive, analyse and refine navigation signals from Global Positioning System (GPS) satellites and transmit the corrections to aircraft, providing GPS signals integrity and enabling Category 1 precision approaches. Establishment of the satellite system is intended to enable the FAA to phase out much of its costly network of ground-based navigation aids.

The FAA has completed work on the hardware for the first phase, including 25 ground stations. It has also completed work on all basic software, but not yet the critical correction and verification software that validates the precise satellite positions, determines the effects of the ionosphere on the GPS signal, and the integrity of the WAAS messages.

"We met all milestones on or ahead of schedule, except for the correction and verification system algorithms," says Raytheon. "We do not anticipate any obstacles to delivery of WAAS."

The Johns Hopkins Applied Physics Laboratory is conducting an independent risk assessment of the use of GPS for civil aviation. The study, due out this month, will help determine whether WAAS can be used as the sole means of navigation for civil aircraft.

Source: Flight International