At busy, big city airports where planes arrive and depart in droves, traffic controllers have powerful radars to help them keep track of the high-speed activity. But planes show up on the crowded radarscopes as small luminous blips that are sometimes difficult to identify properly, and a mix-up of blips may lead to disaster.
At the Atlanta airport a new system designed to dispel such confusion began advanced tests last week. Arriving airplanes make their appearances on the Atlanta scope as the usual blips, which look very much alike, but planes participating in the test carry electronic transponders that send...