The National Transportation Safety Board is holding a media briefing on the mid-air collision last month near Ronald Reagan Washington National Airport.

The National Transportation Safety Board says altimeter in the Black Hawk helicopter may have malfunctioned before the DCA mid-air collision with an American Airlines jet. All 67 people aboard died.

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

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