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).

A midair collision between an Army helicopter and a passenger jet killed all 67 people aboard the two aircraft, officials said, as they search for answers in the nation's deadliest aviation disaster in nearly 25 years.