“We’ve determined that the existing separation distances between helicopter traffic operating on Route 4 and aircraft landing on Runway 33 are insufficient and pose an intolerable risk to aviation safety by increasing the chances of a mid-air collision at DCA,” NTSB Chair Jennifer Homendy said during a news conference.

The crash between a plane from Wichita and an Army Black Hawk helicopter in January has sparked two urgent recommendations to the Federal Aviation Administration.