This data point is one of several key mysteries investigators are exploring as they seek to explain what caused the nation's worst air disaster in more than a decade, aviation experts said.

Dozens of people are dead after a regional jet collided with an Army Black Hawk helicopter Wednesday night over Washington, D.C., officials said, the nation's first major commercial airline crash since 2009.

The soldiers on the helicopter that collided with an American Airlines jet on Wednesday night were from the 12th Combat Aviation Battalion based in Virginia.