That transmission was interrupted — it was stepped on,” said Jennifer Homendy, chair of the National Transportation Safety Board.

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.

Investigators said that an air traffic controller had instructed the Black Hawk crew to pass behind a nearby passenger jet, but that information might have got lost.

Officials at the National Transportation Safety Board said they are looking into the possibility that bad data caused inaccurate readings for the Black Hawk helicopter pilots in the January D.C. crash.

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