The problem Tuesday occurred about 2 p.m. as a number of inbound planes were queued up to turn above Mount Vernon, fly north over the Potomac River and land on National’s main runway. But an approaching storm caused a significant wind shift, and the air traffic control center in Warrenton wanted to reverse the flow of planes into the airport, turning them north of Rosslyn and routing them south along the river to land from the opposite direction…

“The tower agreed, but they didn’t pass it on to all the people they needed to pass it on to,” said a federal official familiar with the incident who was not authorized to speak publicly.

As a result, an incoming flight that had been cleared to land was flying head-on at two planes that had just taken off. The inbound plane and the first of the outbound planes were closing the 1.4 miles between them at a combined speed of 436 mph, a rate that meant they were about 12 seconds from impact when the tower controller recognized her mistake.
National has been the site of some of the most notable incidents, including one revealed last year in which the lone controller supervisor on duty was asleep and didn’t respond when regional controllers sought to hand off planes to National for the final approach.