FAA to simulate GPS outages

The Federal Aviation Administration plans to run a simulation in September to assess the impact of a Global Positioning System (GPS) outage on air traffic control.

The GPS Outage En Route Simulation (GOERS) will test how the loss of satellite-based navigation aids affects controller workload under conditions that include environments in which a mix of GPS and ground-based navigational aids are available.

Jacksonville Air Route Traffic Control Center in Florida is the leading candidate for GOERS, pending coordination with the National Air Traffic Controllers Association (NATCA). The FAA will conduct the simulation across five weeks, then recommend whether measures should be taken to lessen the effects of an outage.

"While the FAA contemplates a reduction of ground-based navigation aids and encourages more reliance on space-based navigation, the impact of a GPS outage must be considered," said Jeff Williams, manager of the air traffic area navigation implementation staff, during a presentation June 4 at the FAA Satellite Operational Implementation Team public forum.

The FAA also will use findings from GOERS to inform future policy decisions. "If the simulation proves the air traffic control system is overly burdened by a large-scale GPS interference event, the FAA's decommissioning plan could be amended," said Terry Mahaffey, a NATCA representative. "The current plan is [contingent upon] the results of GOERS and also" the later GPS Outage Terminal Simulation.

Developed and operated by the Defense Department, GPS allows airborne, land and sea customers to determine their positions anywhere in the world with information from satellites. It is a key technology in battlefield and navigation systems, as well as other critical applications across the public sector.

The FAA, for instance, will use it to help guide airplane landings as part of the Wide Area Augmentation System, a network of ground stations that correct GPS signals and broadcast them to receivers on aircraft.

The latest Federal Radionavigation Plan, released March 26 by the Transportation and Defense departments, maintains the government's commitment to move to satellite-based systems.

Yet a review last year by DOT's Volpe National Transportation Systems Center found that GPS is susceptible to tampering, disruptions from the atmosphere, and blockage by buildings and communications equipment.

Following the Volpe report and the Sept. 11 terrorist attacks, Transportation Secretary Norman Mineta announced that DOT will maintain ground-based navigation systems as a backup for as long as necessary.

The GOERS results will help the FAA determine the extent to which it needs to keep those systems. The study isn't intended to promote a reduction of ground-based capabilities.

The FAA began developing the plan for GOERS in 1998 at a time when it was "basically going to start pulling plugs" or decommissioning all ground-based systems, Williams said.

In 1999, the agency scaled back its approach. "We were right on the verge of doing" GOERS, he said. "When they changed that scenario, it completely altered our simulation variables."

When the Volpe report came out, GOERS was still undergoing revisions. "We were basically on hold until the policy matured," he said. "The current radionavigation plan states a less aggressive decommissioning effort."

The plan calls for reducing the ground-based navigation aids aircraft use to fly across the country by about 50 percent beginning in 2007 and finishing in 2012, according to Mahaffey.

The FAA has amended its GOERS plan to test the impact of reducing those navigation aids to as low as 50 percent, and scenario development is scheduled to begin this month, Williams said.

The GOERS team now is working to secure funding for the project, which will cost about $400,000, he said.

"I think it will be very relevant, especially as we start to decommission [ground-based] navigation aids," Williams said.

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Stimulating simulation

The Federal Aviation Administration has several goals in simulating an outage of the Global Positioning System:

* Gauging the effects of an outage on controller workload.

* Identifying operational issues that could arise during an outage.

* Incorporating lessons learned into a related study scheduled for fiscal 2003.

* Providing a basis for further simulations.