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,

The NTSB is turning the focus of its investigation into the Jan. 29 collision on what the Black Hawk pilots could see and hear.

The Black Hawk pilots who collided with an American Airlines plane last month may not have heard vital information given by air traffic control to fly behind the passenger jet seconds before the crash,