A legacy communications system may have contributed to the nationwide flight halt that disrupted U.S. air travel on Friday, Transportation Secretary Sean Duffy said Saturday. The Department of Transportation does not believe the outage was caused by a cyberattack, he said, while noting that investigators had not determined whether contractor error or equipment failure triggered the problem.
At a news conference in Washington, Duffy said a contractor had been carrying out routine maintenance at a remote Federal Aviation Administration site. The work involved replacing old copper-wire communications lines with fiber-optic lines. The copper system had become obsolete and was due to be taken out of service, he said, making replacement necessary.
Duffy said the work was part of a routine process conducted at sites across the country. However, during the operation, a router being replaced began sending a large volume of connection requests to other routers in the air traffic control network.
“We detected more than 1,000 connection attempts every four to five seconds,” Duffy said. The activity disrupted communications with aircraft and caused some interference with radar data, he said.
Officials imposed a nationwide ground stop after identifying the problem, then worked to isolate the affected equipment. The FAA later restored airspace operations, and the agency said Saturday that air traffic control centers had returned to normal operations.
Duffy said it was not yet clear whether the incident resulted from a contractor’s mistake or a malfunction in the equipment. He described the affected system as an FAA network that did not meet the performance required of it.
Asked whether a foreign government or another actor had launched a cyberattack, Duffy said the administration did not believe that was the case. He said systems returned to operation after officials isolated the work at the remote site. The investigation into the precise cause remained ongoing.
The ground stop was issued Friday after the FAA cited extraordinary circumstances and safety concerns. The agency halted departing flights nationwide while the communications problem was addressed. International arrivals were handled individually during the disruption.
Duffy said about 3,500 aircraft were in the air when the ground stop was issued and that all landed safely. He praised pilots and air traffic controllers for managing the aircraft during the disruption, and also thanked flight attendants, ground crews and airport authorities.
The secretary said the department and the FAA appreciated passengers’ patience as airlines dealt with delays and cancellations. The halt affected air travel across the country, though officials did not provide a final total of canceled or delayed flights at Saturday’s news conference.
New York Governor Kathy Hochul called for Duffy to resign or for President Donald Trump to remove him. In a statement Saturday, Hochul cited what she described as chronic air traffic controller shortages and recurring communications failures, saying they reflected a pattern of problems during Duffy’s tenure. She also urged Congress to conduct a full investigation into the shutdown.
Hochul criticized Duffy’s focus, accusing him of prioritizing television appearances over addressing problems at the Transportation Department. The secretary’s remarks at the news conference focused on the outage, the response by aviation personnel and the ongoing investigation.
The FAA said Saturday that operations across all air traffic control centers had returned to normal. The agency has not released a full technical account of how the router generated the connection requests, how the disruption spread through the network or what safeguards will be introduced to prevent a recurrence.
The episode has renewed attention on the communications infrastructure supporting the national air traffic system. Duffy said the maintenance work was routine and that copper lines were being replaced with fiber-optic connections, but he did not say whether the transition itself caused the outage. Investigators are still examining whether the failure stemmed from the contractor’s work, faulty equipment or a combination of factors.
