Thousands of flights across the United States were snarled on Monday, with incoming flights halted for hours at major East Coast airports, before the Federal Aviation Administration resolved a telecommunications problem late in the afternoon.

The primary communications line failed at a key Federal Aviation Administration facility in Philadelphia and the backup fibre optic line was inadvertently severed by railroad construction workers. That left controllers without radar or communications during the day.

Transportation Secretary Sean Duffy said in an online post that the primary and backup lines were fixed by Monday evening and all airports in the Northeast were operating again. But significant delays were expected to continue through the evening hours.

Hundreds of flights were cancelled at the Newark, LaGuardia, Kennedy and Philadelphia airports. By Monday evening, flights were resuming at all those airports.

Some airlines were allowing customers to change flights without charge. The FAA advised travellers to check the status of their flights before heading to the airport.

FlightAware, a flight-tracking website, said about 7,000 flights were delayed or cancelled, including 1,400 flights at the three major New York-area airports.

The outage happened just as US President Donald Trump and 130 world leaders and dozens of ministers were arriving in New York for the annual high-level meeting of the United Nations General Assembly.

The technical problems stem from the same FAA facility in Philadelphia that caused numerous disruptions at Newark Liberty International Airport in the spring of 2025.

Regional control centres like these have two lines that carry radar and communications data in and out: the primary and the backup. The FAA said a circuit on the primary failed on Monday morning, and when the system tried to switch to the backup, workers discovered that the fibre optic line had been cut.

Earlier in the day, Duffy said an Amtrak construction crew was to blame. Amtrak, however, pointed to a New Jersey Transit construction crew that was working in the area between Newark and New Brunswick, New Jersey.

The incident demonstrated the fragility of the ageing US air traffic control system, which Congress awarded US$12.5 billion for upgrades last year.

FAA Administrator Bryan Bedford said a replacement circuit had failed at Philadelphia Terminal Radar Approach Control, which was the primary communications for the centre.

“The timing is absolutely horrible and I'm very sorry for the delays and cancellations,” Bedford told reporters. He stressed that safety was the top priority.

“We're going to do what is necessary to make sure the airspace is safe.”

The loss of communications was tied to a failed circuit at a Philadelphia air traffic control facility that handles air traffic for the airports, Bedford said. Then authorities discovered that the construction crew had accidentally cut a backup fibre line.

"When it went to flip into the backup, we discovered that the backup fibre had a break, and that fibre break is probably 13 hours to repair. It's massive, I'm told. Meanwhile, we've got the new circuit ready to install now," Bedford said. (Reuters/AP)



Edited by Cecil Wong