Many questions remain unanswered as the investigation into the cause of the American Airlines plane collision with a Black Hawk helicopter in Washington, D.C., continues.

Emergency services on scene after plane and helicopter collide near DC's Reagan Airport Source: Reuters Kournikova, who stays ...

A U.S. Army UH-60M Black Hawk helicopter has completed initial ground runs with two of the new T901 Improved Turbine Engines.