The National Transportation Safety Board will question witnesses Thursday about air traffic control training, a key part of the investigation into January’s deadly midair collision at Ronald Reagan Washington National Airport.

During the hearings, the NTSB was told that the Army helicopter never heard the command from the air traffic controller to "pass behind the CRJ" as the transmission was stepped on. It was also revealed that the plane's pilots were not warned by the controller that there was a helicopter nearby or cleared to fly near the helicopter.

Investigators testifying at a hearing into the January's mid-air crash in DC suggest faulty altitude data may have led to a miscalculation.