The board focused on air traffic control and heard it was common for pilots to ask to use visual separation — relying on eyesight — just as the Army Black Hawk's pilot agreed to do the night of the crash.

Investigators have found that a helicopter involved in a deadly crash with a passenger plane over Washington was flying above its height limit. The helicopter's altitude-measuring instrument was also inaccurate.

The National Transportation Safety Board on Thursday questioned the failure of an air traffic controller to issue a warning about a potential collision in the moments before a crash between an Army helicopter and an American Airlines regional jet that killed 67 people.