A bit more detail on that (Source is Washington Post)
A hotline connecting air traffic controllers at Reagan National Airport and their counterparts at the Pentagon had been “inoperable” since March 2022, a Federal Aviation Administration official confirmed Wednesday.
The line is maintained by the Defense Department, and the aviation agency was not aware of the outage, Franklin McIntosh, the deputy head of air traffic control, testified at a Senate hearing Wednesday. Aviation officials learned of the issue after controllers at National, in Arlington, Virginia, had to order two flights to abandon landing attempts this month due to an Army helicopter heading to the Pentagon.
“We’re insisting on that line to be fixed before we resume any operations out of the Pentagon,” McIntosh said.
The incident this month raised fresh questions about coordination between the military and the FAA in the busy airspace around the airport.
McIntosh confirmed that after the incident, officials weighed whether to suspend an agreement that allows the military to fly in the Washington area without receiving clearance beforehand from the FAA. Before the FAA took that step, however, the Army unit in Virginia announced that it would once again suspend helicopter flights to the Pentagon while it carried out a review.
The Army did not immediately respond to questions about the hotline.