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,

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

Black Hawk pilots may not have heard a critical directive from air traffic control to fly behind the American Airlines plane in the seconds before it collided with the jet, and may have had “bad data” on the altitude they were flying at,