Chicago O'Hare and Midway were ground stopped at 3:10 and 3:13 PM ET for "comms issues"; the nationwide stop (Advisory 111, "due to extraordinary circumstances and for reasons of safety") followed at 20:54 UTC, listed through 11 PM ET. Secretary Duffy cited a communication issue impacting all Air Route Traffic Control Centers; FAA then called it a temporary telecommunications outage. About 4,000 US-bound flights were airborne; airborne aircraft were allowed to land. Cancellations passed 2,400 by 23:45 UTC and Flightradar24 counts more than 13,000 delays or cancellations worldwide. Some international departures resumed case by case; the first O'Hare departure in nearly four hours left about 00:17 UTC with the national stop still in effect. DHS Secretary Mullin said there is no reason to believe it was an attack and pointed to a software update; the FBI is looking at a software update; CBS sources say an update to the L3Harris-run communications network that links air traffic control caused a reboot and crash; CNN sources say airlines were told it began with network routers at Chicago Midway.

What to do: Lifted the evening of Nov 13 (US Eastern), after more than four hours; departures resumed. FAA: a temporary telecommunications outage at the en route centers. Transportation Secretary Duffy: switches and routers got overloaded with data. DHS Secretary Mullin: no cyberattack (The Watchers, Spectrum News, Washington Post).