The Federal Aviation Administration halted U.S. departures on November 13 after a communications outage; San Francisco airport announced clearance for Hawaii- and Asia-bound flights. Its 3:54 p.m. ET order stopped departures until further notice, handling international arrivals individually. United said its airborne flights would continue while new domestic flights stayed grounded.

Transportation Secretary Sean Duffy said technicians were investigating problems at all Air Route Traffic Control Centers. The Guardian, citing CNN, reported FAA briefings on router faults believed to spread from Chicago Midway.

Homeland Security Secretary Markwayne Mullin reported no attack indication, excluded no cause and said Trump was briefed. He assured flyers, prioritized communications recovery and safe landings, and gave no end time with investigation continuing after restoration. Officials from multiple agencies told NBC that initial checks found no signs of malice or typical cyberattacks, but the assessment could change. Three senior officials saw no link indication to the November 12 Microsoft outage. Air Space Intelligence denied its SMART software, products or integration caused the halt.

Vikrant Vaze, a Dartmouth aviation professor, estimated 300,000-400,000 stranded passengers and roughly 3,000-4,000 delayed flights in over two hours, with about 25,000 domestic flights daily. FlightAware recorded over 11,000 delayed or cancelled U.S. flights; Flightradar24 counted 4,042 U.S.-bound flights airborne at the alert.

A source told NBC Reagan National's aircraft parking was full, Chicago O'Hare nearly full by 6 p.m. and diversions possible; Newark tower staff cited parking and gate shortages on LiveATC. Aviation safety expert Jeff Guzzetti said pilots trained for outages had landing backups, but grounded planes could require taxiway parking; he could not explain the cause. NBC Chicago reported prior equipment-related stops at O'Hare and Midway.

British Airways cancelled November 13's 10:30 p.m. Heathrow-New York flight. Manchester airport warned three Virgin Atlantic U.S.-bound flights on the morning of November 14 were likely affected unless the problem was fixed soon. JFK urged checking flight status with airlines before airport travel.

This was the third nationwide halt, after the September 11, 2001, attacks and nearest-airport landings, and January 2023's pilot-alert failure with a domestic pause under two hours. FAA data show over 14,000 controllers and over 44,000 daily U.S. departures. It announced the first U.S. digital towers running in Alaska and Florida in November, to cut delays and improve flow. Congress approved $12.5bn in 2025 for aging FAA communications repairs; the FAA and White House sought another $30.1bn for other issues on November 13.