WASHINGTON (AP) — 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, investigators said Friday.

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 NTSB gave an update Friday on the devastating crash in Washington, D.C., between an American Airlines plane and U.S. Army Black Hawk helicopter.

The National Transportation Safety Board is looking into flight data discrepancies, potential altimeter malfunctions and a possible miscommunication with air traffic control in the midair collision of an Army helicopter and a commercial airplane last month in the deadliest U.

National Transportation Safety Board (NTSB) chair Jennifer Homendy provides an update Friday into the investigation of the Jan. 29 fatal crash between an Army helicopter and an American Airlines jet.