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Controllers Say Computers Causing False Images of Planes

April 20, 1991

CHICAGO (AP) _ Air-traffic controllers around the country say phantom images of airplanes often appear on cockpit computers, but the Federal Aviation Administration says safety isn’t affected.

The pilot of a United Airlines flight approaching O’Hare International Airport on Thursday tried to avoid a plane that wasn’t really there, said Joel Hicks, national director of safety and technology for the National Air Traffic Controllers Association in Washington, D.C.

The incident began when a computer system called T-CAS - Traffic Alert and Collision Avoidance System - told the pilot another airplane was coming toward him, Hicks said.

T-CAS ordered the pilot to descend from 7,000 feet to 6,000 feet, and the pilot began the move. At the same time, another aircraft leaving O’Hare was climbing from 5,000 feet to 6,000 feet.

″The pilot advised (air-traffic controllers) as he was changing altitude,″ Hicks said Friday. ″But more times than not they don’t have time to do that. They’re busy taking the plane up or down.″

Controllers told the United pilot to return to 7,000 feet, and he did, although by law pilots can override information from T-CAS only if they see the other airplane. Controllers and the FAA say the standard separation - the distance pilots must keep between their airplanes - was maintained.

Standard separation within 40 miles of O’Hare is three miles horizontally or 1,000 feet vertically.

FAA officials said the appearance of ″ghost planes″ might be caused by a software problem. They said it has posed no threat to air safety.

″We’re in the process of eliminating a problem in the software that might have caused this,″ said FAA spokesman Mort Edelstein.

″From our standpoint, we know the system works the way it was designed to work,″ he said. ″There was no problem with separation. There was no threat to safety.″

He said the FAA has recorded 750,000 hours of operational use of T-CAS, adding that in all those hours no incidents of planes flying too close together were discovered.

But Hicks charged that the system caused planes being handled by the Washington, D.C., air traffic control center to fly too close to each other earlier this year.

A retired pilot also said the habit of pilots to blindly trust the computer puts them in danger.

″Pilots are in a spring-loaded position to act when one of these devices tells them to, regardless of rhyme or reason,″ said Dick Russell, a retired United captain with 26,000 hours of flying time.

Russell worked on initial tests with the system and now runs an aviation safety consulting company near Los Angeles.

After years of research, the FAA issued regulations in 1989 requiring all commercial aircraft with more than 30 seats to install T-CAS within three years. Officials gave commercial planes with 10 to 30 seats six years to install the system.

T-CAS currently is used in about 20 percent of the nation’s passenger planes, Hicks said.

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