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 National Transportation Safety Board on Tuesday released two reports — one on preliminary findings and another on safety recommendations — related to the deadly collision of an Army Black Hawk helicopter and an American Airlines regional jet in January.