Staffing at the air traffic control tower at Ronald Reagan National Airport was “not normal for the time of day and volume of traffic,” according to an internal preliminary Federal Aviation Administration safety report about the collision that was reviewed by The New York Times. The controller who was handling helicopters in the airport’s vicinity Wednesday night was also instructing planes that were landing and departing from its runways. Those jobs typically are assigned to two controllers, rather than one.

A preliminary investigation report into the crash that occurred between a commercial plane and a military helicopter Wednesday night reportedly showed the air traffic control tower staffing level at Ronald Reagan National Airport, where the passenger jet was headed, was “not normal for the time of day and level of traffic,” The New York Times reported.

The FAA has repeatedly warned that a shortage of air-traffic controllers along the eastern seaboard has forced it to restrict the number of flights it can permit through the area.