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,

The first of the National Transportation Safety Board’s three days of investigative hearings is underway to help determine what caused the deadly midair collision on January 29 between an Army helicopter on a training mission and American Airlines flight 5342 landing at Ronald Reagan Washington National Airport.

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.