After the US ground stop: nearly 8,000 flights cancelled, and a $50 billion overhaul cited for the old system

The US Federal Aviation Administration (FAA) has lifted the longest nationwide ground stop of flights since the 11 September 2001 terrorist attacks.

The FAA said Friday's stoppage, which lasted more than four hours, was due to extraordinary circumstances from a communication issue affecting all air traffic control centres.

According to FlightAware, the ground stop led to more than 8,500 delayed and nearly 8,000 cancelled flights on Friday.

The FAA's initial announcement at 15:54 EST (20:54 GMT) said all flights departing within the US would be grounded until further notice.

More than 3,500 airplanes were in the air at the time; some were diverted to other airports and others flew on to their destinations.

Hours later, some flights were allowed to take off from San Francisco International airport, and the FAA opened the skies again at 20:15 EST.

According to Eurocontrol's website, all US-bound air traffic from its member states was suspended on request of the FAA due to technical issues. Eurocontrol has 42 member states, including dozens of EU nations, the UK, Ukraine and Turkey, as well as Israel and Morocco.

Australia's largest international airport, Sydney, grounded all US-bound flights until further notice, and Air Canada cancelled flights between the US and Canada.

Transportation Secretary Sean Duffy said at a news conference on Friday night that 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,' Duffy said, noting that tens of thousands of people were stranded in airports around the country, many of them without any knowledge of where they were going to sleep that night.

JetBlue cancelled all remaining domestic flights on Friday evening, while Delta Air Lines said it was resuming operations; there was no statement yet from United or American Airlines at that point.

Duffy said a legacy air traffic control communications system became overloaded. 'So this is analogue telecom. Our switches, our routers actually got overloaded with data and they went down,' he said, adding that this had affected communications and radar. The system needs a complete overhaul, he said, estimating a $50 billion price tag.

Homeland Security Secretary Markwayne Mullin told the news conference they had seen zero evidence it was a cyber-attack, and he ruled out any link to the global Microsoft outage that began on Thursday. Mullin said the introduction of some new technology into an old air traffic control system had overwhelmed it.

Both cabinet secretaries insisted the public was never in danger during the stoppage, and Mullin said there was no indication of an attack and that everybody was safe.

It was only the second such nationwide stoppage since the immediate aftermath of the al-Qaeda plane hijackings of 11 September 2001. Dr Guy Gratton, an associate professor of aviation at Cranfield University, told BBC Verify: 'This looks like the worst since 9/11, but clearly not on that scale.' He pointed to a US grounding in 2023 due to a failure in the Notice to Air Missions (Notam) system, which lasted 1 hour and 52 minutes, delayed about 9,500 flights and cancelled about 1,300; Friday's incident lasted longer than that 2023 event.