A jet with 60 passengers and four crew members collided with an Army helicopter while approaching Ronald Reagan National Airport near Washington, D.C., sending the two aircraft plummeting into the Potomac River and killing everyone on board.

Wednesday’s fatal collision and two other incidents dramatically illustrate the challenges pilots and air traffic controllers face in the complex, security-sensitive skies above the nation’s capital.

An American Airlines regional passenger jet and a U.S. Army Black Hawk helicopter crashed into the Potomac River after a mid-air collision near Reagan Washington National Airport on Wednesday night, officials said.