The U.S. halted flight departures across the country for hours on Friday for the second time since 9/11, blaming aging technology that was overloaded, affecting key information for multiple air traffic control centers.
More than 10,000 flights were disrupted during the nationwide ground stop, and delays and cancellations were set to stretch into the weekend, if not longer.
Transportation Secretary Sean Duffy said at a press conference late Friday that that telecommunications routers were overloaded with data. "They went down," he said.
Homeland Security Secretary Markwayne Mullin said Friday at the White House that there was no indication that the issues were a threat to the United States. He later said at a press conference that it doesn't appear to be a cyber attack, and that it "appears this was mechanically driven."
The Federal Aviation Administration canceled the ground stop at 8:15 p.m. ET Friday after it lasted formore than four hours and disrupted the travel plans of hundreds of thousands of travelers, including some college sports teams.
The agency earlier said in post on X that there was a "temporary telecommunications outage" and that it halted flights out of an "abundance of caution."
When it issued the ground stop at about 4 p.m., the FAA said the communications issues were "impacting multiple Air Route Traffic Control Centers." These facilities guide airplanes at high altitudes along their routes.
While the FAA lifted the ground stop, travel chaos continued at airports, which were forced to find places for parked planes. Delays were set to continue even as flights start taking off again.
Carriers canceled more flights as the disruption wore on. JetBlue Airways told staff it would cancel the remainder of the day's flights, aside from European routes, as well as others scheduled for Saturday so that crews and planes are in place to resume operations, according to a memo seen by CNBC.
A ground stop halts flights at their departure point. Disruptions tend to snowball if ground stops drag on as flight crews reach their maximum number of duty hours for a day.
There were 11,000 flights scheduled to depart U.S. airports after 4 p.m. ET on Friday, according to flight-data firm Cirium, with 1.5 million passengers. There were about 600 diverted flights on Friday, 104 of them sent to other airports, Cirium said.
International flights had started taking off from coastal hubs before 6 p.m. ET.
The FAA said earlier in the night that flights will be allowed to depart as en route traffic facilities recover, "through coordination with the air traffic control system."
The FAA's technicians are investigating, the agency said.
Nationwide ground stops are extremely rare. In January 2023, the FAA halted flights because of issues with a pilot alert system. Before that, traffic was halted nationwide after the Sept. 11, 2001, terror attacks.
Aging technology
Technical issues have repeatedly snarled air traffic in the U.S. in recent years. Aging infrastructure and staffing shortages have angered airline executives for years.
In September, hundreds of flights into Newark, New Jersey, and Philadelphia were canceled, delayed or diverted after a Verizon fiber cable was accidentally cut. Officials said it occurred during construction in New Jersey, severing a backup feed of key data for air traffic controllers.
In 2025, air traffic controllers lost contact with aircraft heading to and from Newark Liberty International Airport, an equipment failure that led to massive flight delays and raised more concerns about aging U.S. aviation infrastructure and staffing shortages.
"It's going to continue to fail," Duffy said Friday of U.S. air traffic control infrastructure. The U.S. is in the middle of an overhaul of the technology, and Duffy urged lawmakers for more funding.
Inbound international flights will be managed on a case by case basis, the FAA said.
The major U.S. airlines issued statements saying they would work with customers who were affected by the ground stop and encouraged travelers to check for updates.
— CNBC's Kevin Breuninger and Phil LeBeau contributed to this article.