Investigators suspect the Army helicopter crew that collided with an American Airlines jet near Washington, D.C., might have had inaccurate altitude readings and missed key air traffic controller instructions.

Investigators trying to determine what caused last week’s deadly midair collision between a US military Black Hawk helicopter and an American Airlines plane near Washington, DC, briefed lawmakers Thursday on what they’ve learned after combing through data from both aircraft and air traffic control.

The NTSB said Army Black Hawk crew may not have heard a message to "pass behind" the D.C.-bound passenger plane before the Jan. 29 midair crash over the Potomac River.