Photo credit, EPA
The U.S. Federal Aviation Administration has lifted the longest nationwide suspension of ground flights since the terrorist attacks of September 11, 2001.
The FAA said Friday's air traffic interruption, which lasted more than four hours, was "due to exceptional circumstances" related to a communications problem affecting all air traffic control centers.
Homeland Security Secretary Markwayne Mullin said there was no indication of an attack and everyone was safe.
Here's what we know.
How many flights were affected?
The grounding resulted in more than 8,500 delays and nearly 8,000 flight cancellations as of Friday, according to FlightAware.
The FAA's initial announcement at 3:54 p.m. EST (8:54 p.m. GMT) said all flights departing from the United States would be grounded until further notice.
More than 3,500 planes were in the air at that time. Some were diverted to other airports, while others continued on to their destinations.
Hours later, some flights were allowed to depart from San Francisco International Airport.
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The Federal Aviation Administration has reopened airspace until 8:15 p.m. EST.
What about international flights?
According to the Eurocontrol website, all air traffic to the United States from Eurocontrol member states has been suspended "at the request of the FAA due to technical issues."
Eurocontrol has 42 member states, including dozens of EU countries, the United Kingdom, Ukraine and Turkey, as well as Israel and Morocco.
Australia's largest international airport, Sydney, has suspended all flights to the United States until further notice.
Air Canada has canceled its flights between the United States and Canada.
When will normal service resume?
Transportation Secretary Sean Duffy said at a news conference Friday evening that the outage would have repercussions for a few days.
“It's going to take us some time to sort out what happened this afternoon,” Duffy said.
Tens of thousands of people were stranded in airports across the country, many of them “without knowing where they were going to sleep tonight,” Duffy said.
Delta Air Lines and United Airlines have announced the resumption of their flights.
American Airlines said it was "working to secure as many remaining flights as possible this evening." JetBlue announced the resumption of its flights Saturday morning.
What caused the ground to stop?
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Duffy said an existing air traffic control communications system had become overloaded.
“So it’s analog telecommunications. Our switches and routers were overloaded with data and crashed,” Duffy said.
He said this affected communications and radars. The system requires a complete overhaul, he said, estimating the cost at $50 billion.
“It’s going to continue to fail,” he said.
Homeland Security Secretary Markwayne Mullin said at the press conference that they had seen "no evidence" that it was a cyberattack.
He also ruled out any link to the global Microsoft outage that began on Thursday.
Mullin said introducing new technology into an old air traffic control system overwhelmed him.
Both ministers insisted that the public was never in danger during the shutdown.
When was the last ground stop?
It was only the second such nationwide shutdown since the al-Qaeda attacks of September 11, 2001.
“It looks like the worst disaster since 9/11, but clearly not on this scale,” Dr Guy Gratton, associate professor of aviation at Cranfield University, told BBC Verify.
Dr Gratton spoke of a US grounding in 2023 due to a failure of the air mission notification system (NOTAM).
“It lasted 1 hour and 52 minutes, delayed around 9,500 flights and canceled around 1,300,” he said.
The 2023 outage prevented air safety advisories from being issued and flights were grounded until the system was returned to service.
But Friday's incident lasted longer than the one in 2023.
We used AI to help translate this article, originally written in English. A BBC journalist checked the translation before publication. Learn more about how we use AI.
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