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May 7, 1999 By MATTHEW L. WALD

An air traffic control computer on Long Island that is the first of a new generation being installed nationwide failed early Thursday, creating havoc at LGA, EWR and Philadelphia Airports.

Two hundred and seventy-four departing airplanes were delayed, some for more than an hour, according to a spokeswoman for the FAA, who said that the number of incoming planes delayed was unknown. Tens of thousands of travelers were inconvenienced by the problem.

The failure is another sign that the air traffic control system, long plagued by breakdowns of frail, obsolete equipment, faces more breakdowns with the installation of new hardware and software to replace components that are either not compliant with year 2000 computer standards or are obsolete.

The computer system that failed had begun operation Feb. 24, and its timely installation was hailed by the F.A.A. as a sign of the agency's increasing ability to modernize its equipment. The new computers are replacing a model that is about 10 years old, that is not year 2000 compliant and for which vital replacement parts are not available.

The problems yesterday apparently occurred when the new computer was linked to a new type of display screen for the controllers. The screens, which are being installed nationwide, have better resolution than the old ones and can show more data.

The old computer system, called the Host, knits together data from a variety of radars and supplies it to controllers' screens. The replacement system, called the Host Computer System Replacement and known as Hocsr, is not new. But the I.B.M. Corporation, its manufacturer, still supplies parts for the system.

The system that failed yesterday is at the New York Air Route Traffic Control Center, in Ronkonkoma, N.Y., adjacent to MacArthur Airport in Suffolk County. The F.A.A. is centers, which generally handle longer-distance, higher-altitude planes.

"We haven't had this type of problem with the Hocsr before," said Arlene Salac, the F.A.A. spokeswoman. "Certainly we are concerned about it."

Henry Brown, an official with the union that represents F.A.A. electronics technicians, said the new system had not been thoroughly checked before it was turned on.

"They rushed this system into service, against our wishes, because they want to say we've got another 40 percent of our equipment Y2K compliant," he said.

Mr. Brown, who represents New York-area members of the Professional Airways System Specialists, said the failure came as technicians tried to connect the new computer to the new group of display screens, which is part of another modernization project. The switch, though, may have thrown more data at the new computer system than it could handle, he said.

When the new computer system failed yesterday at 6:25 A.M., the old one automatically took over, but it, too, promptly malfunctioned.

Ms. Salac said F.A.A. officials had not determined the cause of the computer failure, but she confirmed that it came as the system tried to switch from one computer to the other.

After the two computer systems failed, a third system was put into use.

But since that system does not provide as much data, air traffic controllers had to increase the spacing between planes to 20 miles from 10, Ms. Salac said.

As a result, EWR recorded 146 departure delays, and LGA recorded 80, for an average of 41 minutes. The maximum delay at EWR was an hour and 13 minutes, and at LGA, an hour and 3 minutes, according to Ms. Salac.

Planes had to be spaced out at JFK also, she said, but "we don't have much traffic at J.F.K. in the morning," and there were no delays. At Philadelphia, 48 departing planes were delayed an average of 28 minutes; the maximum was 51 minutes.

Ms. Salac said that the F.A.A. would not tally arrival delays until today, and that she did not know whether that number was likely to be larger or smaller than the number of departure delays.

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