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The United States Federal Aviation Administration lifted a nationwide ground stop on Friday evening after more than four hours — the longest such halt to domestic air travel since the immediate aftermath of the 11 September 2001 attacks — following a failure in legacy air traffic control communications equipment that officials said had nothing to do with a cyber-attack or an ongoing Microsoft outage.
The FAA issued its initial grounding order at 15:54 Eastern time, citing “extraordinary circumstances” from a communication issue affecting all air traffic control centres. Flights were cleared to resume at 20:15 Eastern. At the time the order was issued, more than 3,500 aircraft were already airborne; some were diverted to alternate airports while others continued to their destinations. Hours into the stoppage, limited departures were permitted from San Francisco International Airport before the full lifting of restrictions.
By the end of the day, the disruption had produced more than 8,500 delayed flights and nearly 8,000 cancellations, according to tracking service FlightAware. Tens of thousands of passengers were stranded in terminals across the country, many of them, in the words of Transportation Secretary Sean Duffy, “without any knowledge of where they’re going to sleep tonight.”
Analogue infrastructure blamed
Speaking at a news conference Friday night, Duffy said the failure originated in a legacy analogue telecommunications system. “Our switches, our routers actually got overloaded with data and they went down,” he said, adding that the overload had affected both communications and radar. He estimated that a complete overhaul of the air traffic control system would cost $50 billion and warned the ageing infrastructure “is going to continue to fail.”
Homeland Security Secretary Markwayne Mullin said investigators had found “zero evidence” of a cyber-attack and ruled out any connection to the global Microsoft outage that began on Thursday. Mullin attributed the collapse to new technology being introduced into an old system, which overwhelmed it. Both cabinet secretaries insisted the public was never in danger during the stoppage.
International ripple effects
The grounding extended well beyond US borders. Eurocontrol, which coordinates air traffic across 42 member states including EU nations, the United Kingdom, Ukraine, Turkey, Israel and Morocco, suspended all US-bound traffic “on request of the FAA due to technical issues.” Sydney Airport, Australia’s largest international hub, grounded US-bound flights until further notice. Air Canada cancelled flights between the US and Canada.
Delta Air Lines and United Airlines said they were resuming operations Friday evening. American Airlines said it was “focused on operating as many remaining flights as possible this evening,” while JetBlue said it would not restart flights until Saturday morning. Duffy cautioned that the disruption would produce a ripple effect lasting several days. “It’s going to take us some time to unwind what’s happened this afternoon,” he said.
Worse than 2023, but a different scale from 9/11
The only comparable nationwide stoppage in recent memory occurred in January 2023, when a failure in the Notice to Air Missions system grounded flights for one hour and 52 minutes, delaying roughly 9,500 flights and cancelling about 1,300. Friday’s event lasted more than twice as long. “This looks like the worst since 9/11, but clearly not on that scale,” Dr Guy Gratton, an associate professor of aviation at Cranfield University, told BBC Verify. The 2001 grounding followed the al-Qaeda hijackings and kept US airspace closed for days.