QUICK TAKE | Why the US Ordered Its Longest Nationwide Flight Ground Stop Since 9/11. Seven Things to Know

1. How long did the US stop flights from taking off?

The Federal Aviation Administration halted departures nationwide on Friday, November 13, after a telecommunications failure disrupted air traffic control. The FAA lifted the order at 8:15 pm Eastern time, more than four hours later.

2. How many flights were affected?

FlightAware recorded more than 8,500 delays and nearly 8,000 cancellations on Friday, the BBC reported. The delays alone were fewer than during the 2023 ground stop, but cancellations were roughly six times as high.

3. What happened to the planes already in the air?

More than 3,500 aircraft were airborne when the order came down. Some continued to their destinations and others were diverted. The FAA said it had accounted for every flight. A ground stop holds departures while controllers manage the aircraft already in the air.

4. What failed?

Transportation Secretary Sean Duffy said data overwhelmed switches and routers in a legacy analogue telecom network, disrupting communications and radar. Homeland Security Secretary Markwayne Mullin said officials had seen no evidence of a cyberattack or a link to the Microsoft outage. Duffy put the cost of overhauling the air traffic control system at about $50 billion.

5. Why were flights outside the US held back?

At the FAA’s request, Eurocontrol suspended US-bound traffic from its member states, which include the UK and much of Europe. Sydney Airport also held US-bound departures. The disruption therefore reached passengers whose flights had yet to enter American airspace.

6. Why did delays continue after the FAA lifted the order?

Aircraft and crews were out of position, and some crews were approaching their duty limits. Delta began resuming operations, while JetBlue cancelled its remaining domestic flights that evening. Duffy said the disruption could take days to unwind.

7. What made this the longest nationwide stop since 9/11?

The previous nationwide halt, in January 2023, lasted one hour and 52 minutes, according to aviation researcher Guy Gratton, speaking to BBC Verify. That failure took down the system that distributes safety notices to pilots. Friday’s outage lasted more than twice as long and affected the network controllers use to manage flights.