The pilots of a Black Hawk helicopter that collided with a passenger jet near Washington Reagan National Airport in January never heard an air traffic controller's instruction to pass behind the jet,

Three days of investigative hearings on the deadly midair collision over Washington in January began Wednesday, aiming to reveal new insights into what caused the crash between a passenger plane and an Army helicopter that killed 67 people.

The National Transportation Safety Board said on Wednesday that testing showed faulty altitude data in U.S. Army helicopters like the one that collided with an American Airlines plane on January 29, killing 67 near Ronald Reagan Washington National Airport.