Safety Bubbles in the Sky

The FAA approves a new system to avoid collisions

Still as trim and erect as he was in his days as a Marine test pilot, J. Lynn Helms, 56, the new Federal Aviation Administrator, climbed aboard a little two-engine Cessna, throttled down the runway at Washington National Airport and gave chase to a Boeing 727. He made six breathtakingly close passes at the larger aircraft, almost as if he were knocking MiGs out of the skies over Korea. Last week, several days after that acrobatic performance, Helms disclosed what he had decided as a result of the flight. By 1984, he announced, a new electronic warning system would be "absolutely and firmly" in operation on U.S. aircraft.

The decision, welcomed by both commercial and private aviation circles, capped a controversy over appropriate anticollision gear. The device that passed the old Marine's personal muster is a bureaucratic mouthful: Threat Alert and Collision Avoidance System (TCAS, for short). But there is nothing complex about its goal: to avoid disastrous collisions like the one that caused the deaths of 144 people when a small private plane crashed into a commercial jet over San Diego in 1978. The risk of similar mishaps--25 occurred in 1979 (the latest year tabulated) with the loss of 34 lives--could become greater in the future. Today there are about 220,000 aircraft in the U.S. fleet. In the next decade, Helms estimates, 100,000 more planes will be crisscrossing the once spacious U.S. skies.

Largely an outgrowth of work done at M.I.T.'s Lincoln Labs in collaboration with the FAA and private industry, the winning system meets two basic requirements. It can be produced in a relatively cheap (as little as $2,500) bare-bones version suitable for small private aircraft, yet it will also be compatible with sophisticated versions (costing $50,000) for larger commercial aircraft. In whatever form, no assistance is needed from controllers or radar stations to determine when planes veer dangerously close.

That protection comes from inquiring signals constantly emitted from TCAS-equipped planes. These radar-like pulses in effect create an electronic cocoon or bubble extending out in all directions from an aircraft for up to 22 nautical miles. If another plane pierces the bubble, its presence is almost instantly noted in the cockpit. In the cut-rate TCAS-I, an alert sounds and lights up. In the more complex TCAS-II, a cockpit screen not only displays the intruder's position (at 2 o'clock, say), distance and altitude but also tells the pilot whether to dive, climb or just remain on course to avoid disaster. The action taken will automatically be passed on to the other plane.

The new system is not foolproof. Neither version will be able to spot a plane that does not carry at least a transponder, which indicates a plane's location to inquiring signals from the ground or another aircraft. But such planes are already forbidden to fly in busy air lanes near major cities. Adds Helms: "Sure, there is still a possibility of a collision, but the probability will be drastically reduced." Besides, allows the ex-Marine pilot, the only way to get 100% protection is "to ground all planes except one." Presumably, with Helms in the cockpit.

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