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Technology Allows Better Tracking of Planes

Could help prevent runway, mid-air collisions
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CAMBRIDGE, Mass.--A relatively inexpensive technology developed by MIT researchers will allow better tracking of planes and move such surveillance into the satellite age. The technology, which will be demonstrated three times over the next two months, will also improve surveillance of trucks and other vehicles on the runway.

The new technology takes advantage of the Global Positioning System (GPS), a network of satellites that can accurately determine the position of a given object to within 10 meters. Dubbed GPS-Squitter, the technology determines a plane's position via GPS then squitters, or broadcasts, that position--plus the plane's identification--to all listeners.

Those listeners include not only air-traffic controllers, but other planes. As a result, it allows aircraft to see each other, a feat that is not practical for all aircraft today because the radar equipment to do so is very expensive. "Now for only a few thousand dollars, you can have a receiver on any plane to pick up squittered information from other planes," said Dr. Steven R. Bussolari, leader of the MIT Lincoln Laboratory group that developed GPS-Squitter.

In addition to being an added safety measure, the ability for planes to see each other could pay off in other ways. For example, currently there is no aircraft surveillance over many ocean flyways because there is no place to put the radar ground station that sends and receives the pulses of energy that determine a plane's position.

"Air traffic controllers keep planes separated over the ocean by sending them off about 100 miles apart," Dr. Bussolari said. "This extra separation ensures they won't get close enough to hit, since the controllers can't track their progress on radar." If planes could see each other, "you could safely pack them in much tighter to really take advantage of the airway."

GPS-Squitter, which recently won a 1995 R&D 100 Award, has other advantages over radar. For example, the ground stations that receive the squittered information (not to be confused with the smaller receivers on each plane) are much less expensive than radar ground stations (~$100,000 versus $4-5 million).

Dr. Bussolari noted that GPS-Squitter will also improve surveillance of planes and other vehicles that are on the runway. He explained that a big plane can sometimes shadow a smaller plane, blocking the radar signals that would ordinarily have alerted controllers to the presence of the smaller plane. GPS-Squitter solves this problem because each aircraft sends out its own signals, and GPS-Squitter ground stations are so inexpensive that several could be located around the airport so signals can't be blocked.

Two major demonstrations of GPS-Squitter were conducted in 1994. One tested surface surveillance of aircraft at Logan International Airport; the other tested air surveillance of helicopters servicing oil platforms in the Gulf of Mexico. Both demonstrations were successful, producing performance results that matched theoretical predictions.

Three more demonstrations should take place over the next two months (December 1995- January 1996). One will test low-cost collision avoidance receivers for private aircraft; it will take place in the Los Angeles area. The other two, which will test different aspects of the system, will be carried out at Hanscom Field in Bedford, Massachusetts, and in the air over New York City.

The work is supported by the Federal Aviation Administration.

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