A report indicates the duties of handling military helicopters and commercial flight arrivals were combined on Wednesday evening

The responsibility of handling air traffic control for helicopters and incoming planes at Reagan National Airport were combined on Wednesday night ahead of a deadly collision, a report said.

Sometime before an American Airlines flight crashed into an Army Black Hawk helicopter over the Potomac River, an air traffic controller was assigned both duties by their supervisor, the New York Times reported,citing a source briefed on staffing and an internal preliminary FAA safety report.

Usually, the duties of handling helicopter traffic and managing planes are divided from 10 a.m. to 9:30 p.m. at the airport, the Times reported. After 9:30 p.m., when traffic slows down, those duties may be combined.

However, on Wednesday, an air traffic control supervisor combined those duties sometime before 9:30 p.m. and allowed one air traffic controller to leave the job early, the Times reported.

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