THE US DEPARTMENTS of Defense and Transportation (the DoD and DoT) have reached an agreement allowing the Federal Aviation Administration to implement the wide-area augmentation system (WAAS), which will make the global-positioning system (GPS) "fully usable for all phases of civil flight".

The Pentagon has been convinced that localised jamming of WAAS signals is technically feasible, and could be used in a limited war to deny an enemy access to augmented civil-GPS accuracy within the theatre of operations.

The awarding of the WAAS contract is scheduled for 15 May, and the system is to be operational in late 1997, increasing the integrity and availability of GPS to allow sole-means use for en route navigation and non-precision approach. Error-correction broadcasts to increase GPS accuracy, allowing Category I precision approaches, will be phased in between 1998 and 2001.

The DoD plans tests in April to determine whether the L1 frequency, which carries civil-GPS and WAAS signals can be jammed effectively. Nine tests totaling 45h are planned, and jamming could affect all commercial receivers within a 500km (270nm) radius. The FAA says that the tests "...will not hold up WAAS implementation".

To allay fears that the DoD would deny civil users access during a time of war, US President Bill Clinton, in a statement to the International Civil Aviation Organisation (ICAO), says that the USA "...remains committed to provide GPS signals to the international civil-aviation community and to other peaceful users."

An international WAAS demonstration, involving the USA, Italy, India, Australia and New Zealand, is planned, covering eastbound routes linking North America and the Far East. Each of the countries, will use its own ground testbeds, to broadcast integrity and availability data, via Inmarsat communications satellites.

The FAA says that Clinton's statement underlines the Government's support for civil GPS use "at the highest level". The Agency's GPS programme manager, Dick Arnold, says: "There is very strong interest in the US Government in using GPS to the best possible advantage to levy taxpayers' dollars. Civil use of GPS is important to the military."

Source: Flight International