By late Saturday, airlines in the United States had cancelled more than 900 flights scheduled for Sunday, as they continued to recover from a nationwide ground stop imposed by the Federal Aviation Administration.
FlightAware, a flight-tracking service, recorded 910 cancellations for Sunday, and the figure was still rising.
The service also recorded more than 6,400 cancelled flights on Saturday, following about 9,200 on Friday.
The FAA order had halted nearly all departing flights for almost five hours on Friday.
The order was lifted that evening, but passengers still faced cancellations and delays as airlines worked to reposition aircraft and crews.
FAA Administrator Bryan Bedford said, “I do think the worst is behind us,” but added that “a significant amount of recovery work” remained.
He also apologised to travellers, saying: “I’m sorry that we put you through this, but we did it for the right reasons.”
US Transportation Secretary Sean Duffy said the disruption began during work to replace old copper telecommunications lines with fibre-optic cables at an FAA facility.
According to him, a router involved in the upgrade overloaded parts of the network, which affected air traffic communications and radar systems.
“We had over 1,000 connection attempts every four to five seconds,” Duffy said.
He added that the surge caused “issues with our communication with airplanes” and disrupted radar feeds.
Officials are investigating whether the problem resulted from an installation error or faulty equipment.
“We haven’t determined what the fault was,” Duffy said.
Bedford said airlines expected to restore their schedules by late Sunday.
“Based on everything that we’re hearing from our airline partners, they believe that they’ll be able to have full schedule integrity by the close of business on Sunday,” he said.
The FAA said it ordered the ground stop as a safety measure after communications problems affected 17 of its 22 en-route air traffic control centres.
Bedford said, “No facilities went dark. Nothing was fully lost.”
He also said there was “zero evidence of anything nefarious, and zero evidence of anything AI-related.”
