The New York Times's live updates track a rare nationwide F.A.A. ground stop declared Friday afternoon, which reporter Karoun Demirjian says appeared to be a major outage of the air traffic control system, with more than 7,800 flights delayed and about 350 canceled by late afternoon per FlightAware. Homeland Security Secretary Markwayne Mullin blames a telecommunication outage, says it is not a terrorist attack and that officials do not yet know the cause, while the disruption lands about two weeks before Thanksgiving and days after the F.A.A. began rolling out a new A.I. tool that it is unclear whether the outage involves.