An airspace cluttered with passenger planes and military aircraft. A history of near-crashes. And a growing shortage of air traffic controllers available to manage it all. Some experts, politicians and airport managers have been warning for years of the risks posed by the crowded airspace and volume of flights at Ronald Reagan Washington National Airport (DCA).

Before the additional flights were approved, a senator warned that the increase could heighten the risk of collisions.

Investigators analyze flight data to understand the crash between an American Airlines jet and a military helicopter and exactly what was going on before disaster struck.