A report has revealed that the responsibilities of managing military helicopters and commercial flight arrivals were combined on Wednesday evening before a deadly midair collision.

At Reagan National Airport, an air traffic controller was assigned both duties by their supervisor ahead of a crash involving an American Airlines flight and an Army Black Hawk helicopter over the Potomac River, the New York Times reported, citing a source briefed on staffing and a preliminary FAA safety report.

Normally, helicopter and plane traffic are managed separately from 10 a.m. to 9:30 p.m. After 9:30 p.m., when traffic decreases, the roles may be merged. However, on Wednesday, an air traffic control supervisor combined them before 9:30 p.m. and allowed a controller to leave early.

The FAA’s preliminary safety report found that staffing at the airport was “not normal for the time of day and volume of traffic,” according to the Associated Press.