US airspace reopens after four-hour grounding triggers 6,600 cancellations

US airspace reopened at 8:15 p.m. Eastern Time (0115 GMT) on Friday after a four-hour nationwide grounding that canceled more than 6,600 flights, delayed another 8,600 and left another 1,500 flights already scrubbed for Sunday, according to FlightRadar24.

Transportation Secretary Sean Duffy told reporters at the White House that departures would resume only gradually. "It's going to be slow," he said. Aviation analysts warned the outage could disrupt airline schedules for days, and Duffy said tens of thousands of passengers were stranded at airports across the country.

For air cargo and belly-capacity users, that means days of repositioned aircraft, displaced crews and thinned international lift before networks normalize.

What actually failed?

Duffy traced the trouble to 3:36 p.m., when air traffic control centers experienced instability in their radar and communications systems. The cause, he said, was prosaic and internal: data overloaded the hardware.

"Our switches, our routers actually got overloaded with data and they started to give us inconsistencies in the data from those routers and because of that we shut the system down," Duffy said.

At no stage, he stressed, did controllers completely lose radar or communications, and thousands of planes landed safely. The immediate problem has been fixed and flying is safe, he said — but a broader overhaul is needed to prevent a repeat.

Two airline officials said the outage appeared to affect a telecommunications network overseen by L3Harris Technologies, which handles the critical radio frequencies controllers use to talk to pilots. L3Harris did not respond to a request for comment.

Cyberattack ruled out — for now

Homeland Security Secretary Markwayne Mullin said there was "zero evidence" so far that the outage resulted from a cyberattack or a rogue AI system, though investigators have not ruled out either possibility.

"It appears this was mechanically driven, however, we're still looking," Mullin said. The National Security Agency is working with DHS on the investigation.

Duffy said he and Mullin had met President Donald Trump in the Oval Office to discuss the outage.

A $50 billion repair bill

The failure is the latest and most dramatic sign of strain on a US air traffic control system beset by aging technology, equipment and communications problems — plus a shortage of several thousand controllers.

Duffy blamed Congress for failing to fund a replacement system and called for $50 billion to modernize it. Earlier on Friday, before the outage, the White House and the Department of Transportation had already urged Congress to approve $30.1 billion to upgrade the nation's aging airports and ATC infrastructure.

"What we have is an incredibly old air traffic control system," Duffy said. "Give us the money to fix it."

The scale of the grounding is historically rare. The only other nationwide ground stop since the September 11 attacks came in January 2023, when the FAA halted domestic departures for about 90 minutes. Friday's stop ran roughly four hours.

What does this change for shippers and airlines?

On compensation, the answer for passengers is blunt: none is required. US airlines will not have to compensate stranded travelers because the carriers were not responsible for the FAA system failures.

Investors priced the hit immediately. Shares of American Airlines, United Airlines and Delta Air Lines fell between 1% and 2% in after-hours trading, while JetBlue Airways dropped about 3%.

American Airlines said it was prioritizing flights to smaller cities outside its major hubs and international destinations to position aircraft and crews for a faster recovery — a sequencing choice that delays mainline frequency but restores network geometry faster.

Passengers still stuck

From Boston to Seattle and New York to Los Angeles, passengers crowded departure halls and airline desks as delays and cancellations mounted and aircraft stayed parked at gates. Thousands faced overnight stranding.

Edward Kargbo, 50, from West Chester, Pennsylvania, had been booked on a 9 p.m. Ethiopian Airlines flight to Lomé, Togo. Instead, he planned to spend the night at the airport before a rescheduled 6 a.m. Saturday departure. "I have to squat the night here," he said. "I'm stranded."

Louise Maher, 47, was caught at Newark when her British Airways flight to London was caught up in the meltdown. "I might cry at some point but not yet," she said.

With aircraft and crews out of position and analysts expecting multi-day schedule disruption, the operational question now shifts to Congress: whether the $30.1 billion request — or Duffy's $50 billion figure — gets funded before the next aging router gives out.