Mid-Air Payoff

By early 1967, U.S. commercial aviation experts had spent a decade vainly trying to develop a highly reliable midair collision-avoidance system (CAS). The number of "near misses" by U.S. aircraft had risen to more than 400 a year; the air traffic problem would soon be compounded by the arrival of jumbo jets and the SST. Alarmed, the Air Transport Association in January started an urgent program joining six avionics manufacturers* in the search for a solution. Last week the ATA triumphantly anounced the payoff; the blueprint for a CAS that could make the skies as safe as a sailing pond.

The new system hinges on the installation of an atomic clock and a 40-lb. computer mechanism in every U.S. commercial aircraft. At three-second intervals, precisely timed signals from the computers would surround each aircraft with a protective electronic bubble. When one bubble touched another, the system would trigger an audio-visual alarm and possibly give the pilots a harmless electric shock. In today's jets, the warning would come 60 seconds prior to possible collision, when the aircraft were about 20 miles apart. Twenty seconds later, after electronic analysis of courses, speeds and altitudes, the sensor-computers would signal the best possible collision-avoidance maneuver each pilot should execute, such as "stop turn" or "stop climb."

30-Second Synch. The basic element in the system is electronic measurement of the distance between aircraft, each of which must carry an atomic timepiece synchronized to a network of ground-based master clocks. In places where master-clock stations are not feasible, such as remote ocean areas, one plane would take over as the master clock, and all other planes in the sector would synchronize with it. The whole system would operate at dazzling speed: 196 converging aircraft, all of whose clocks were completely unsynchronized, could sort themselves out and synchronize in 30 seconds.

At roughly $40,000 per plane, the new CAS will be relatively inexpensive, and the ATA hopes to put it in operation by 1971. Budget planning for testing and refining a prototype has already begun. Says ATA president Stuart Tipton: "We believe this can be the starting point for a common national system for airborn collision avoidance --a goal we are determined to reach."

* The McDonnell Co., Bendix Radio, Collins Radio, National Co., Sierra Research Co. and TRG, a subsidiary of Control Data Corp.

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