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).

The airspace where a deadly mid-air crash between a passenger plane and a U.S. Army Black Hawk occurred late Wednesday night is one of the most complex and congested in the country.