It is the second of three days of witness testimony and public inquiry by the National Transportation Safety Board into the January midair crash over the Potomac River.

Long-standing concerns about military helicopters flying in crowded airspace and worries over short staffing among federal aviation workers have emerged as key factors in investigators’ inquiry into the fatal midair crash between an Army helicopter and a commercial airliner earlier this year.

Military helicopter traffic over Washington was a longtime worry among aviators operating around the airport where an Army helicopter and commercial airliner collided this year, killing 67 people, federal investigators heard during testimony on Thursday.