A long list of things went wrong in January and contributed to the collision between an Army helicopter and an American Airlines jet over Washington, D.

Aviation experts told the National Transportation Safety Board that night vision goggles may have created viewing difficulties for the pilots of a U.S. Army helicopter that collided with a passenger jet over Washington in January.

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.