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.

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.C., sending the aircraft plummeting into the Potomac River and killing everyone on board.

A jet carrying 60 passengers and four crew members 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.