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 National Transportation Safety Board said the helicopter’s cockpit voice recorder didn’t capture key directions from air-traffic control and is investigating whether the crew might have seen a different altitude on the flight instruments.

The National Transportation Safety Board gave an update on its investigation into the deadly midair collision between an American Airlines plane and a Black Hawk helicopter.