In January, 67 people died when an American Airlines passenger flight crashed with a military helicopter near Washington, D.C.

The pilots of a Black Hawk helicopter that collided with a passenger jet near Washington Reagan National Airport in January likely didn’t know how high they were flying or how close they were to an airliner before the deadly crash,

Incorrect altitude readings on the Army helicopter that collided with a passenger plane over Washington, D.C., in January contributed to the aircraft getting too close, but air traffic controllers warned about the hazards helicopter traffic presented years before the crash.