Pilots have long worried about the congested and complex airspace around the airport near the heart of the capital, where flights must maneuver around military aircraft and restricted areas. It was no secret there had been previous close calls, but the numbers found by the NTSB were alarming.

The NTSB’s preliminary report on the Jan. 29 crash that killed 67 people said current helicopter routes allowed around the airport are an ‘intolerable risk to aviation safety.’