FAA lifts four-hour nationwide ground stop, longest since 9/11

The US Federal Aviation Administration lifted a nationwide ground stop on Friday after more than four hours, the longest such stoppage since the 11 September 2001 attacks.

The FAA said the halt was "due to extraordinary circumstances" from a communication issue affecting all air traffic control centres. Its initial announcement at 15:54 EST (20:54 GMT) said all flights departing within the US would be grounded until further notice; the agency opened the skies again at 20:15 EST. More than 3,500 airplanes were in the air at the time, some diverted to other airports and others flying on to their destinations.

FlightAware counted more than 8,500 delayed and nearly 8,000 cancelled flights on Friday.

Eurocontrol suspended all US-bound air traffic from its member states "on request of the FAA due to technical issues". The organisation has 42 member states, including dozens of EU nations, the UK, Ukraine, Turkey, Israel and Morocco. Australia's largest international airport, Sydney, grounded all US-bound flights, and Air Canada cancelled flights between the US and Canada.

Transportation Secretary Sean Duffy said a legacy air traffic control communications system became overloaded. "Our switches, our routers actually got overloaded with data and they went down," he said, adding that communications and radar were affected. He estimated a complete overhaul at a $50 billion price tag and warned: "It's going to continue to fail."

Homeland Security Secretary Markwayne Mullin said there was "zero evidence" of a cyber-attack and ruled out any link to the global Microsoft outage that began on Thursday. He said the introduction of new technology into an old air traffic control system had overwhelmed it. Both cabinet secretaries insisted the public was never in danger.

Duffy said the outage would cause a ripple effect for a few days. "It's going to take us some time to unwind what's happened this afternoon," he said. Tens of thousands of people were stranded in airports. Delta Air Lines and United Airlines said they were resuming operations, American Airlines said it was operating as many remaining flights as possible, and JetBlue said it would resume on Saturday morning.

Dr Guy Gratton, an associate professor of aviation at Cranfield University, said the incident looked like "the worst since 9/11, but clearly not on that scale". He noted that a 2023 grounding caused by a failure in the Notice to Air Missions system lasted 1 hour and 52 minutes, delayed about 9,500 flights and cancelled about 1,300.