Also Gives Directions on What to Do : Computer Warns Pilots of Threat of Collision

The Federal Aviation Administration has developed an airborne computer system that warns pilots of potential midair collisions and gives directions on how to avoid them.

FAA officials said the Traffic Alert and Collision Avoidance System--dubbed TCAS--would make the skies safer when installed by commercial carriers on their jetliners in the coming years.

The government does not plan to order the airlines to make the installation, but expects major carriers to do it on their own. Early next year, Piedmont Airlines will fly the first aircraft in commercial service to be equipped with the collision avoidance system.

The system is estimated to cost between $50,000 and $70,000 for each aircraft, considered a small investment in helping protect multimillion-dollar airplanes.

The airlines and the government have invested heavily to perfect the device, which uses time, not distance, as it measures the threat of collision between two aircraft.

A cockpit computer tracks all transponder-equipped planes that are nearby and projects the time that each will take to collide with the aircraft. All commercial aircraft and most other planes are equipped with transponders, devices that receive signals and send back responses on crucial information regarding airplane locations.

Just 40 seconds before a threat of a midair crash, the collision avoidance system gives out a loud beep in the cockpit and advises the pilot with a synthetic voice to either climb or descend to avoid an accident. The warning is repeated a few seconds later and the beep stays on unless the pilot executes the change in altitude.

The FAA demonstrated the system last week to a small group of reporters aboard a plane whose pilot carefully executed several planned near-collisions.

Every time another aircraft came close, the collision avoidance system alerted the pilot.

Joe Fee, acting manager for the project at the federal agency, said the device--especially useful in remote areas--would complement existing air traffic control.

“It worked perfectly,” Fee said of the demonstration. “The test showed the system is ready to go on aircraft. It is probably the best-tested system the FAA has ever had.”

The device might have prevented the midair crash in San Diego seven years ago, in which 144 people died when a Pacific Southwest Airlines Boeing 727 and a Cessna 172 collided.