Pilots have long worried about the congested and complex airspace around Reagan National, 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 uncovered more than 15,000 “near-miss events” between helicopters and jets at Reagan National airport in just three years leading up to the American Airlines jet and Army helicopter collision that killed 67 people.

There's an "intolerable risk to aviation safety" with helicopters and planes flying too close to one another near DCA.