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The high volume of commercial flights is overloading the air control computer systems at many airports, handicapping efforts to maintain safety in the nation's skies, according to a new government study.

Inadequate computer capacity has forced air-traffic control screens to go blank at 27 of the nation's 63 largest airports at least once in the last year-and-a-half, said the General Accounting Office, the investigative arm of Congress. The screens carry data -- such as a flight's position, speed and destination -- crucial for the prevention of midair collisions.

In a separate report, the GAO said there were 1,158 reported near-collisions in midair involving commercial carriers in the last three years, 70% of them "serious." It defined as "serious" cases in which aircraft are less than 500 feet apart.

Copyright Dow Jones & Company Inc Jul 18, 1989

WASHINGTON -- The high volume of commercial flights is overloading the air control computer systems at many airports, handicapping efforts to maintain safety in the nation's skies, according to a new government study.

Inadequate computer capacity has forced air-traffic control screens to go blank at 27 of the nation's 63 largest airports at least once in the last year-and-a-half, said the General Accounting Office, the investigative arm of Congress. The screens carry data -- such as a flight's position, speed and destination -- crucial for the prevention of midair collisions.

In a separate report, the GAO said there were 1,158 reported near-collisions in midair involving commercial carriers in the last three years, 70% of them "serious." It defined as "serious" cases in which aircraft are less than 500 feet apart.

The total number of near-collisions jumped 43% in 1987 to 489 cases, then dropped to 326 last year.

Although there was no explicit link made between the computer failures and the numbers of close misses, the GAO said that "existing computer capacity shortfalls at some large, busy {airports} are impairing controllers' ability to maintain safe separation of aircraft."

GAO Assistant Director Joel Willemssen cited one example of computer failure in which all information disappeared from controllers' screens for 16 minutes during the Friday rush hour last Oct. 7 at the Dallas-Fort Worth airport. Atlanta's airport has also experienced "several instances" when screens went blank for up to 20 minutes at a time, the report said.

The phenomenon known as "sector loss" occurs when data from large numbers of airplanes overwhelm the air traffic computer system. According to the GAO, the Federal Aviation Administration's 1960s-era computer system has grown obsolete and unable to handle the sharp rise in commercial air traffic brought on by deregulation.

An FAA safety rule, which took effect July 1, will only worsen the situation, the GAO said. The regulation requires all planes flying near 23 high-density airports to be equipped with a Model C transponder, which transmits flight information to air traffic controllers.

About 44,000 additional aircraft -- mostly smaller planes -- will thus pop up onto controllers' screens, greatly increasing the chances of sector loss, the GAO said. About 110,000 planes currently carry similar devices, said a spokeswoman for the Aircraft Owners and Pilots Association.

Both the association and Sen. Frank Lautenberg (D., N.J.), chairman of the Senate Transportation Appropriations Subcommittee, have criticized the new rule as dangerous. "It doesn't make sense if an effort to improve safety at one level degrades it at another," Sen. Lautenberg said in a statement. "If these computers can't handle the additional signals, we should put in place a system that can."

Credit: Staff Reporter of The Wall Street Journal