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.

A jet with 60 passengers and four crew members collided with an Army helicopter while preparing to land at Ronald Reagan National Airport near Washington, D