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.

Washington, DC (CNN) — In more than 32 hours of testimony across three days the National Transportation Safety Board probed virtually every detail of what led up to the January 29 midair collision between a US Army Black Hawk helicopter and an American Airlines regional jet, operated by PSA airlines.

A three-day hearing into the January mid-air collision between an Army Blackhawk helicopter and an American Airlines jet concluded today. The National Transportation Safety Board's hearing focused on the breakdown of safety systems that led to the deaths of 67 people,