More details about the plane crash that killed NASCAR driver Greg Biffle and his family have emerged amid an investigation by the National Transportation Safety Board, but officials remain unsure of who was flying the plane. "At this time, we have been unable to verify who was flying the airplane," NTSB board member Michael Graham said in a press conference held Friday, December 19. "We do know three of the occupants did possess a pilots' license but we have been unable to verify this at this time. That is one of the things we're working on.