Thousands of US flights cancelled after grounding

The US Federal Aviation Administration has lifted a nationwide grounding of flights after a communications failure at air traffic control centres caused chaos at US airports.

The ground stop triggered the longest US flight shutdown since the 11 September 2001 attacks.

US airspace reopened at 1.15am Irish time but US Transportation Secretary Sean Duffy warned that departures would resume gradually and it would take time for airlines to restore normal operations.

"It's going to be slow," Mr Duffy told reporters at the White House.

By 11:30pm, nearly 10,000 flights had been cancelled, including more than 2,200 each at Delta Air Lines and American Airlines, and 1,800 at United Airlines, according to Flightradar24.

The plane-tracking website said some aircraft at major airports had waited more than five hours for a gate.

The four-hour nationwide grounding could disrupt airline schedules for days, aviation analysts said.

Mr Duffy said tens of thousands of passengers were stranded at airports around the country.

Mr Duffy said he and Homeland Security Secretary Markwayne Mullin had met with US President Donald Trump in the Oval Office to discuss the outage.

The failure is the latest and most dramatic sign of strain on a US air traffic control system beset by aging technology, equipment and communications problems and a shortage of several thousand controllers.

Mr Duffy said the trouble began at 3:36pm, when air traffic control centres ‌experienced instability in radar and communications systems.

"Our switches, our routers actually ⁠got overloaded with data and they started to give us inconsistencies in the data from those routers and because of that we shut the system down," Mr Duffy said, adding that at no stage did they completely lose radar or communications and they were able to safely land thousands of planes.

Mr Duffy said the immediate problem had been fixed and that flying was safe, but warned that a broader overhaul of the aging air traffic control system was needed to prevent similar failures.

Some flights between Ireland and US cancelled

Dublin Airport has warned that flights between Ireland and the US could be affected this morning, with delays and a small number of cancellations possible.

Passengers are being advised to contact their airline directly for the latest updates.

Outbound flights to Chicago and New York were cancelled this morning.

Two incoming flights from Chicago and one from New York were cancelled this morning.

Flights from New York, Dallas, Atlanta and Minneapolis were among those experiencing delays.

Dublin Airport said it will work closely with airlines to help impacted passengers.

Mr Duffy blamed Congress not funding a new system that he said could prevent such outages, and called for $50bn to modernise it.

Earlier yesterday, before the outage, the White House and Department of ‌Transportation had urged Congress to approve $30.1bn to upgrade the nation's aging airports and air traffic control infrastructure.

"What we have is an incredibly old air traffic control system," Mr Duffy said. "Give us the money to fix it."

Homeland Security Secretary Mr Mullin said there was "zero evidence" so far that the outage resulted from ⁠a cyber attack or a rogue AI system, though investigators had not ruled out either possibility.

"It appears this was mechanically driven. However, we're still looking," Mr Mullin said.

The National Security Agency was working with the ‌Department of Homeland Security on the investigation, he added.

The outage appeared to be affecting a telecommunications network overseen by L3Harris Technologies, according to two airline ⁠officials.

The network handles ‌critical radio frequencies used by air traffic controllers to communicate with pilots. L3Harris did not respond to a request for comment.

Though the ground stop was lifted, the disruption for passengers was far from over. From Boston to Seattle and New York to Los Angeles, passengers crowded departure halls and airline desks as delays and cancellations mounted and aircraft remained parked at gates.

US airlines will not be required to provide compensation to stranded passengers because the carriers were not responsible for the FAA system failures.

The only other nationwide ground stop since the 11 September attacks came in January 2023, when the FAA halted domestic departures for about 90 minutes.

Investors were already pricing in a financial hit to airlines. Shares of American, United and Delta fell between 1% and 2% in after-hours trading, while JetBlue Airways dropped about 3%.

American Airlines said it was prioritising flights to international destinations and to smaller cities outside its major hubs to position aircraft and crews for ‌a faster recovery.