Transportation Secretary Sean Duffy said he takes responsibility for Friday’s nationwide flight shutdown and acknowledged that he did not anticipate the scale of the outage, as American Airlines began working to operate its remaining evening flights and Alaska Air Group reported disruptions across both of its carriers. National Air Traffic Controllers Association President Nick Daniels said controllers were “handling something that’s never been seen before” as they guided roughly 4,000 airborne planes to safety after the Federal Aviation Administration halted departures at 3:54 p.m. ET.

The FAA lifted the 4 hour and 25 minute ground stop at 8:15 p.m. ET after telecommunications issues at 3:36 p.m. ET disrupted facilities and TRACONs nationwide, leading to more than 5,000 cancellations, over 10,000 delays and at least 1,500 Saturday cancellations, including nearly 40% of JetBlue’s schedule. While Homeland Security Secretary Markwayne Mullin said patches and new equipment installed by the FAA were “overwhelming the older system,” the Transportation Department denied that new technology deployments caused the failure and blamed overloaded 1980s copper lines and legacy switches and routers. CBS News reported that an update to the private communications network operated by L3Harris Technologies caused the system to reboot and crash.