Three of the nation's busiest airports -- La Guardia, Kennedy and Newark -- ground to a halt yesterday because of a power failure at a major AT&T telephone switching center in lower Manhattan, representing the worst aviation communication failure in recent memory.
The outage, which began at 4:50 p.m., caused a logjam at XTC airports across the region, including Baltimore-Washington International and Philadelphia, where airplanes bound for New York were being held pending restoration of communication lines in New York.
"Airplanes that are on the ground are staying there, and other flights are being rerouted," said Agnes Huff, a spokeswoman for USAir in Los Angeles.
As of last night, Ms. Huff said, about 85 USAir flights across the Northeast had been canceled as a result of the outage.
"We've had minor outages which affected small areas before, but nothing like this," she said.
The outage affected a major routing site in New York that monitors air traffic into and out of the New York airports. Known as a Terminal Radar Approach Control facility, or TRACON, the site allows federal air traffic controllers in different cities to exchange information from radar facilities about en route aircraft. That information is exchanged over phone lines.
With the New York TRACON down and towers unable to talk to each other, the New York airports were forced to shut down.
Fred O'Donnell, a spokesman for the Federal Aviation Administration in Los Angeles, described the outage as a "major safety issue" for the nation's airports.
"As far as we are concerned, when you lose communication it automatically becomes a safety issue," he said.
The outage blocked many long-distance calls into and out of the New York area, said Jim McGann, an AT&T spokesman. It affected domestic as well as international calls, and toll-free 800 telephone numbers originating or terminating in New York.
As of 8:45 p.m., AT&T was predicting partial restoration of service within the hour. But the company still did not know what had caused the problem.
AT&T technicians were working into the night to determine the cause of the outage. AT&T denied one unconfirmed report that a cable was cut but could neither definitively confirm or deny a report of an explosion at a telephone switching site.
"We don't think there's anything to that," Mr. McGann said. "As far as we can tell, we're still talking about a power supply problem."
Mr. McGann was unable to provide information about AT&T's power supply system, or to say why a failure in one of three New York switching centers affected such a broad area.
AT&T's network has built-in redundancy, meaning failures in one part of the network are supposed to cause a backup route to kick in automatically. It was not clear why AT&T's backup mechanisms did not immediately rectify the problem.
The New York outage occurred late enough in the day to avoid disrupting most New York area businesses.