Last month, an American Airlines passenger jet and an Army helicopter collided as the plane prepared to land at Washington D.C.’s Ronald Reagan National Airport.

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.

A key safety system was turned off on the U.S. Army helicopter that collided with an American Airlines regional jet last week near Washington's Reagan Airport, killing 67.

National Transportation Safety Board Chairwoman Jennifer Homendy told reporters that the recording from the Black Hawk helicopter cockpit suggested an incomplete radio transmission may have left the crew without understanding how it should shift position just before the Jan.