ADS-B Gets Green Light, GPS Backup Less Clear

 - October 7, 2010, 12:04 PM

Following successful ADS-B deployment at key sites in Alaska, the Gulf of Mexico, Louisville and Philadelphia, the FAA recently gave the go ahead for the system’s national rollout, with coast-to-coast U.S. coverage forecast in 2013. The agency’s announcement also stated that wide-area multilateration (Wam) “will serve as a backup to ADS-B in the event of a GPS outage in high-value airspace.” The FAA did not define high-value airspace , but it possibly includes that surrounding the nation’s 35 Operational Evolution Plan airports. Puzzlingly, however, the FAA has an expert panel currently examining GPS backups, with its recommendations still to be made, while the agency’s final ADS-B rule in May downplayed Wam as a backup candidate. Possibly, this is a pre-emptive FAA strike, following continuing concerns of the Government Accountability Office in September that the Department of Defense cannot be certain that the GPS constellation will always provide adequate civil coverage before 2018. The expert panel’s recommended solutions might also not be widely available commercially to counter any early GPS outages.