The Army helicopter that crashed into an American Airlines jet in Washington, D.C. may not have heard important instructions from air traffic controllers, according to the National Transportation Safety Board.

Investigators said that an air traffic controller had instructed the Black Hawk crew to pass behind a nearby passenger jet, but that information might have got lost.

That transmission was interrupted — it was stepped on,” said Jennifer Homendy, chair of the National Transportation Safety Board.

Official tells reporters that recording from Black Hawk helicopter suggests incomplete radio transmission might have left crew without an understanding of how it should shift position