A significant issue may have stemmed from the military Blackhawk helicopter involved in the collision - the lack of the Traffic Collision Avoidance System (TCAS) in military helicopters.

Transportation safety investigators are seeking to determine if the pilots of the American Airlines plane detected danger just before the midair crash with a helicopter.

This crash comes just over a month after a passenger jet crashed in South Korea – possibly as a result of a bird strike – killing all but two of the 181 people on board ...