An air traffic controller at Reagan National Airport reportedly left early on Wednesday before the deadly collision between an American Airlines flight and a military helicopter.

Some major US airports had less than 60% of their staffing targets filled with fully certified controllers in recent years, CNN review finds

The National Transportation Safety Board has interviewed the air-traffic controller who was working at the time of the midair collision, board member Todd Inman said, adding that the interviews have been ongoing throughout the day.