A preliminary analysis of the flight data and voice recorder on board a Black Hawk helicopter leading up to the collision with a commercial flight over Washington, DC, on January 29, indicated the helicopter’s altimeter may have been inaccurate and the pilots may not have heard some calls from the Reagan National Airport control tower,

A military helicopter was carrying out a secretive training mission when it collided with an American Airlines passenger jet, the details of which are mostly “classified,” officials

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.