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 jet with 60 passengers and four crew members aboard collided Wednesday with an Army helicopter while landing at Ronald Reagan National Airport near Washington, prompting a large search-and-rescue operation in the nearby Potomac River.