Prediction precision

When it comes to predicting where aircraft will be in 20 minutes or so, air traffic controllers' crystal balls are pretty hazy. Systems used today rely on flight plans, radar signals and weather data to determine where an aircraft will be at any given time with questionable accuracy.

But with improved safety and smoother traffic management in mind, NASA is testing a system that could help controllers see into the future with much more precision.

Last month, workers at NASA's Ames Research Center, Moffett Field, Calif., announced the completion of a six-month test of the En-route Data Exchange (EDX) system. With EDX, NASA officials monitored 1,000 takeoffs, landings and overhead flights at the Denver Air-Route Traffic Control Center, one of 21 centers that manage flights between airports. The EDX program obtained real-time flight data from 48 Boeing Co. 777s owned by United Air Lines Inc. and specially configured with software from Honeywell International Inc. and delivered it to the center.

Until now, such data had never been extracted directly from planes and provided to ground controllers electronically, said Rich Coppenbarger, EDX technical lead. Real-time flight information including a plane's weight (which changes as fuel is consumed), airspeed, latitude and longitude and updated flight plans are essential to making accurate position predictions, he said.

"We're trying to predict trajectories that are 20 to 30 minutes in advance, and it requires very precise information," Coppenbarger said. "Those trajectory predictions are only as good as the data going into that process." Honeywell's Airplane Condition Monitoring System, configured for the 777, accessed the planes' flight-management systems and acquired information researchers needed for the test.

Radar coverage, flight plans filed with the Federal Aviation Administration and atmospheric conditions can all help controllers forecast positions with some accuracy, "but there's nothing better than the information that resides on the actual flight-management system on board the aircraft," Coppenbarger said. "EDX gives us a way to get it right from the horse's mouth: from the management system."

Knowing where a plane will be in the near future would go a long way toward helping controllers make more informed decisions, Coppenbarger said. Potential conflicts with other planes would be detected much earlier than can be done today. That would improve safety and save time and fuel because correction maneuvers could be made earlier and therefore would be less pronounced.

Also, more efficient landing and takeoff sequences and overall traffic management around airports would improve, said Steve Quarry, staff engineer for airspace electronics systems at Honeywell.

The EDX system "makes the prediction and the traffic management problem a little more precise," Quarry said. "This would make the predictions more accurate, and therefore the quality of [air traffic control] decisions could be better."

Simply having controllers ask pilots to tell them where they expect to be wouldn't work because the radio waves are already congested, and controllers and pilots have enough work as it is, Coppenbarger said. A data link the transmission of information between planes and controllers "is really the only feasible way of getting this kind of data," he said.

EDX technology wouldn't support air traffic controllers directly, said Mike Hawthorne, program manager for control- pilot data link communications in the FAA's Free Flight office. It would instead be used to support air traffic tools under development in the Ames center's Center-Tracon (Terminal Radar Approach Control) Automation System, including the Traffic Management Advisor, the Descent Advisor and Direct-To.