Investigators say the crew of the helicopter that collided midair with an American Airlines jet near Washington D.C.’s Ronald Reagan National Airport might not have heard instructions from the air traffic controller to pass behind the plane.

The crew of the Army helicopter that collided in midair with an American Airlines jet near Washington, D.C.’s Ronald Reagan National Airport may have had inaccurate altitude

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.