US ground stop: US flights are slowly resuming as Duffy blames legacy air traffic systems.
Transportation Secretary Sean Duffy says the U.S. ground stop began at 3:36 p.m., when radar and communications at air traffic control and TRACON centers became unstable. He said more than 3,500 planes were in the air, with less than 400 remaining at the last check, and that critical medevac and medical flights were still allowed.