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.

National Transportation Safety Board officials said Friday that a key transmission from Reagan National Airport’s air traffic control tower may not have been heard by Army Black Hawk helicopter pilots just before they were collided with an American Airlines regional jet last month,

The National Transportation Safety Board is also studying whether the pilots of the Black Hawk in last month’s collision were seeing accurate data about the helicopter’s altitude.

The Black Hawk that collided with an American Airlines jet in January may not have had accurate altitude readings, investigators said.