The Federal Aviation Administration has issued a temporary ground stoppage on all flights in the United States after a communications issue that affected air traffic control centers.

The extraordinary move caused havoc at airports across the country and affected thousands of flights. It’s unclear when the ground stop will end. Homeland Security Secretary Markwayne Mullin confirmed that it was a telecommunications outage and that the ground stop did not constitute a national security threat.

“There is no indication that we’ve had, no reason to believe, that as of right now this was a threat to the United States,” Mullin told reporters at the White House, later repeating there was “no indication as of yet that this was a nefarious attack against us.”

The stoppage was announced Friday afternoon and it’s unclear how long it will last. It marks the second full ground stop since the Sept. 11, 2001, terrorist attack on the World Trade Center in New York. The most recent full ground stop, which lasted about 90 minutes, was in 2023 when a pilot notification system went down.

“Due to extraordinary circumstances and for reasons of safety,” the FAA advisory read, “all departing traffic should remain ground stopped until further notice.” Inbound international flights would be handled “on a case by case basis,” according to the agency.

As of 5:30 p.m. Eastern time, there were more than 9,900 flights delayed across the United States and about 900 cancellations, according to FlightAware, a flight-tracking website. At Los Angeles International Airport, more than 550 flights were delayed and 47 had been canceled.

Shortly after 6 p.m. Eastern it appeared that some flights were being permitted to resume. Hawaiian/Alaska Airlines confirmed that all of its West Coast flights will resume, the Hawaii Department of Transportation wrote on social media.

The Republican staff of the Senate Commerce Committee, which oversees the FAA, wrote on X that the ground stop highlighted the need to prioritize modernizing air traffic control centers. Congress recently passed legislation dedicating $1.9 billion to replace the aging facilities.

“No new ARTCC has been built since LBJ was in office,” they wrote on X.

The outage comes days after the FAA announced it would be rolling out an artificial intelligence tool nationwide to help avoid flight delays. The tool, Strategic Management of Airspace, Routes, and Trajectories, known as SMART, is a cloud-based platform system that was billed as an enhancement to existing FAA air traffic management systems by providing a shared, data-driven view of the national airspace.

Mullin told reporters that officials are looking at any links between the new system and the stoppage. But in a post on social media Friday afternoon, the AI company that created SMART, Air Space Intelligence, said that “current ground stop is not based on or a result of the SMART system, any product of ASI or our integration with FAA and ATC.”

Sen. Tammy Duckworth, D-Ill., the ranking Democrat on the Aviation, Space and Innovation Subcommittee, said she will be demanding answers from the FAA about the ground stop.

“The safety of our skies is built on redundancies. Whatever led to the nationwide ground stop will warrant a thorough and complete investigation,” she said in a statement.

In audio posted by the ATC, a controller could be heard announcing the ground stop to pilots on the runway at San Diego International Airport.

“That’s a joke, right?” a pilot responded in disbelief. The air traffic controller confirmed that it was not a joke, and said the ground stop was due to an issue with equipment.

Multiple voices on the channel then speculated that the outage was related to Thursday’s Microsoft Outlook outage, but the controller said he could not confirm the cause.

Mullin told reporters on Friday that he did not believe the telecommunications issue was tied to the earlier Microsoft Outlook outage.

In Chicago Air Route Traffic Control Center audio, an air traffic controller said they “lost all frequencies and automation for handoffs and strips,” likely in reference to handing off which towers handle which flights and the electronic records used to track individual planes.

At Denver International Airport, a pilot and controller confirmed that the stop was expected to last for more than six hours. In audio from the ATC, the controller said the ground stop was in effect until 9 p.m. local time, or 11 p.m. Eastern.

California’s Office of Emergency Services is reaching out to federal and state officials to determine the extent of the impacts on the state’s airports and passengers, Gov. Gavin Newsom’s press office wrote on X.

Airlines operating across the country were scrambling to notify passengers, many of whom had already arrived at airports expecting to board a plane only to be met with delays and cancellations.

“Flights already in the air can continue to their destinations. We expect disruption to our schedule for the rest of the day, depending on the length of the FAA’s nationwide ground stop,” an American Airlines spokesperson told The Times. “It will be all hands on deck across American to get customers on their way as soon as possible when the FAA lifts this ground stop.”

United and Delta airlines have posted updates on their websites to alert passengers.

“The FAA has issued a nationwide ground stop. New domestic flights will not depart while the FAA ground stop remains in place. International departures are being managed on a case-by-case basis by the FAA. United flights that are already airborne will continue, but diversions are occurring due to the number of airplanes on the ground at our hubs. Cancellations are being implemented due to congestion in the nation’s air traffic system,” United wrote on its website.

Dylan Schroeder, 37, had already boarded a plane in Charlotte, N.C., around 3:45 p.m. Eastern Time, headed for Orlando when the pilot made an unusual announcement.

“Once everyone was on board,” he said, “the pilot came on saying Air Traffic Control was having system issues.”

The pilot said they’d stay on the plane for an update, and after just over an hour announced that the passengers would deplane.

Schroeder, a Baton Rouge resident, said the overall mood on the plane was decent “considering the circumstances.” Several passengers who appeared to be going to Disney World appeared to be disappointed.

In an interview on Friday, Rep. Ted Lieu, D-Calif., said that the FAA telecommunications outage was completely unacceptable and that the agency needs to create systems that do not have a single point of failure.

“I urge the FAA and the Trump administration to make sure this never happens again,” he said.

The California congressman said there needs to be congressional hearings on the cause of the technical issue and improvements enacted.

“What just happened is enormously damaging to trust in our air system,” he said, “and our air system is a vital component of our national economy.”

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Staff writers Kevin Rector, Richard Winton, Grace Toohey and Nilesh Christopher Philip contributed to this report.

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