FAA orders GPS risk assessment

With the future of one of its major modernization programs on the line, the Federal Aviation Administration and two aviation groups have hired Johns Hopkins University to test whether the satellite-based Global Positioning System can provide the only navigation service for airlines, freeing up the FAA from maintaining costly backup systems.

The GPS risk assessment study— funded by the FAA, the Air Transport Association and the Aircraft Owners and Pilots Association— will help the FAA make some important technical and program decisions about its $3 billion Wide Area Augmentation System program. WAAS, being developed by Raytheon Systems Co., will use a network of ground stations to refine GPS signals so that the signals are reliable enough for navigation across the country and for precision approaches to airports.

However, earlier this year a report on critical infrastructures released by a presidential panel cautioned the FAA not to rely on GPS as its sole navigation system. According to the panel, GPS is vulnerable to jamming, lacks redundancy and may not be wholly reliable, leaving aircraft vulnerable to flying blind.

The study, which was awarded to Johns Hopkins' Applied Physics Lab for about $700,000, will determine whether the FAA needs an independent backup system for WAAS and how much such a system might cost. Johns Hopkins plans to release a draft of its findings this fall, with a final report due out in January.

"Don't let the dollar amount fool you; this is a very important study," an FAA spokesman said. "One of the main things this study will look at is WAAS as sole means, meaning no backup system is necessary, vs. WAAS as primary means. The bottom line is to determine which obstacles exist to WAAS...in the future."

"Politically, I think this study is very significant," said Doug Helton, vice president of regulatory policy at the Aircraft Owners and Pilots Association. "I think there are a lot of known answers, but no one has pulled it all together. No one has said, 'Here's the big picture.' "

The risk assessment study is an "important part of the operators gaining confidence in the system and the [GPS] signal," a Raytheon spokesman said. "We view it as a necessary part of the deployment process of WAAS. We welcome the scrutiny."

The FAA contract was awarded because of increasing pressure from Congress to make decisions about the future of WAAS. For example, the Senate FAA reauthorization bill for fiscal 1999, which the Senate may vote on this week, would require the FAA to submit a timetable for implementing WAAS and to make a determination about whether WAAS will require a backup system.

Meanwhile, the Senate FAA appropriations bill would allow the FAA to spend money on WAAS only after the agency had addressed certain issues, such as whether WAAS can be certified as the sole means of navigation so that the FAA will not have to maintain backup systems.

Although legislative interest in WAAS is nothing new, this year Congress is putting more pressure on the FAA to "either fish or cut bait" with WAAS, a Senate staffer said. "We're prodding them into action and laying down hard and fast deadlines."

Raytheon said it is making progress on WAAS. It has installed 25 reference stations, which check GPS satellite signals for errors and then pass them on to master stations that uplink augmented signals to a communications satellite, which then sends the signals back to an aircraft receiver. Raytheon also has installed two master stations and four radio frequency uplinks. Three of four planned software builds are also complete.

"So far there's been a lot of money thrown at WAAS, but it won't be operational until next year," Helton said. "If [Congress] undercuts the program [now], we don't see a lot of sense in that. Even critics of WAAS say we should put at least the initial system out there in 1999." WAAS initial operational capability is scheduled for March 1999.

"The discussion about whether we need a backup system is premature until the risk assessment is done," said Jack Ryan, at the Air Transport Association. "The study will identify problems with GPS-WAAS and provide solutions to the problem. It will either give [WAAS] a clean bill of health or will point out where the problems are."


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