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 readings in the moments before the crash,

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.

Official tells reporters that recording from Black Hawk helicopter suggests incomplete radio transmission might have left crew without an understanding of how it should shift position