Graham Warwick/WASHINGTON DC

A new airspace system modernisation plan drawn up by the US Federal Aviation Administration will retain at least one-third of the existing ground-based navigation and landing aids beyond 2015.

The plan, expected to be released within a month, also foresees the introduction of automatic dependent surveillance - broadcast (ADS-B) between 2003 and 2007.

The FAA had hoped to begin decommissioning ground-based navaids after 2000 as the wide area augmentation system (WAAS) came on line, but concerns over jamming of global positioning system (GPS) signals have made it likely that some will have to be retained as back-ups.

Similarly, the USA had planned to begin removing instrument landing systems as the local area augmentation system (LAAS) came on line. Although a formal decision on whether GPS needs a back-up has yet to be taken, it is seen as inevitable.

The new baseline modernisation plan, called the National Airspace Architecture 1998, sees "half to two-thirds" of the ground-based navigation and landing aids being phased out between 2005 and 2010, with one-third being retained indefinitely to back up the GPS.

The plan is based on the phased introduction of "free flight" technologies, as proposed by advisory body RTCA (Flight International, 23-29 September). Phase 1 (1998-2002) is mainly ground-based, involving the deployment of prototype decision-support systems at key locations. These systems are deployed nationally in Phase 2 (2003-2007), allowing limited free flight operations to be achieved in Phase 3 (2008-2015).

Use of ADS-B for domestic air traffic control is planned to be phased in beginning in 2005, and will follow evaluation of air-to-air ADS-B starting in 2000. The FAA plans to select datalink technologies for ADS-B by late 2003 - the failure to agree on a datalink has held up progress. The FAA is pursuing Mode S and says: "Other technologies will be determined by the [aviation] community."

The new plan is scaled back considerably from the FAA's previous modernisation blueprint, which proved too expensive. Speaking at the RTCA '98 symposium in Washington DC on 30 September, FAA Administrator Jane Garvey urged the community to "resist the temptation" to deviate from the phased modernisation plan.

"Free Flight Phase 1 will do the job. It will provide incremental steps directly leading to modernisation and it will prove that we can do what we say on time and on budget. Congress is watching, we must prove we can deliver," she said.

The phased modernisation plan is the result of an RTCA-brokered consensus agreement between the airlines, general aviation, pilots and controllers unions and the government.

Source: Flight International