What caused the national ground stop? Here is what we know
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WASHINGTON — For more than four hours, a ground stop for virtually all aircraft in the United States brought unprecedented chaos and delays that are expected to last through the weekend.
Here is what we know about what went wrong.
What caused the stop?
Issues with the Federal Aviation Administration’s air traffic control system began when a contractor was performing routine maintenance at a remote FAA location, Transportation Secretary Sean Duffy said at a Saturday morning news conference.
L3Harris Technologies was replacing outdated copper wire with fiber-optic cables when the new equipment began flooding other routers in the air traffic control system — sending more than 1,000 connection attempts every four to five seconds, Duffy said. As a result, communications and radar were interrupted, prompting the FAA to make the rare call to ground all flights nationwide.
It’s unclear whether the root cause was human technician error or faulty equipment.
The Federal Aviation Administration issued a ground stop Friday for all flights in the United States, according to an advisory from the agency.
“We haven’t determined what the fault was,” Duffy said. “Was it the router, or were they not doing great work for us at L3Harris?”
A spokesperson for L3Harris said the company is supporting the FAA’s investigation into the cause of the incident and takes seriously the impact the ground stop had on travelers, airlines and air traffic operations.
What problems did this cause?
The technological breakdown led to intermittent communication and radar, but not a complete blackout, Duffy said.
“We were able to keep some of those communications going, but when you have issues and you can’t immediately communicate, and immediately see where aircraft are at — that’s a risk that we’re unwilling to tolerate,” he said.
The ground stop was implemented in the name of public safety and lasted more than four hours, until the FAA brought the system back online safely.
What do we know about the technology?
Duffy lambasted the aging infrastructure that the FAA relies on and said President Trump is pushing for the funding needed to update the equipment.
“None of your networks run on 1980 technology,” he said to the gaggle of reporters at a Friday evening news conference. “You have all got fiber, state-of-the-art, high-speed networks that cover all of your stations, but not the FAA.”
He said the FAA was in the process of upgrading its air traffic control system thanks to $12.5 billion in funding secured through Trump’s Big Beautiful Bill Act.
L3Harris is leading the massive project to convert the FAA’s aerospace communications from copper wire to a fiber-optic system, which is 70% complete.
On Saturday, Duffy urged Congress to approve an additional $30 billion funding request to complete the modernization of the system and upgrade aging infrastructure at U.S. airports.
Some Democratic members of Congress questioned the demand for additional money, pointing out that of the $12.5 billion approved to upgrade the air traffic control system in July 2025, only $4.3 billion has been obligated.
What is the impact?
There were more than 3,500 airplanes flying in U.S. airspace when the decision to close the airspace was made, Duffy said.
Of the 50,000 flights scheduled Friday, around 9,000 commercial flights and 3,000 private jet flights were unable to complete their journeys, according to FAA Administrator Brian Bedford.
Tens of thousands of travelers were left stranded, and the Federal Emergency Management Agency was mobilized to ensure passengers received lifesaving medication, said Homeland Security Secretary Markwayne Mullin. Some college football teams were left scrambling to find alternative transportation to this weekend’s games.
The FAA estimates that an additional 4,000 to 5,000 flights would be canceled Saturday and hopes airlines will be able to resume regular scheduling by end of business Sunday, Bedford said.
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