The Federal Aviation Administration (FAA) is experimenting with a new system that does not include radar. The testbed is the Colorado area. The new system uses 20 sensors clustered around four airports within the Rockies. The sensors monitor radio broadcasts from the aircraft. By measuring minute differences in the time it takes for the broadcasts to reach the various sensors, as slim as 10 billionths of a second, computers can determine the location, said Ken Tollstam, vice president of Sensis, which built the devices.

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