A preliminary FAA report on the midair collision Wednesday night in Washington describes staffing in the air traffic control tower at that time as "not normal for the time of day and volume of traffic." Assignments that usually were split between two controllers were being handled by one, per the New York Times, which has seen the report. So the Ronald Reagan National Airport controller handling helicopters in the area also was giving takeoff and landing instructions to planes, the report says.
Such doubling up is common when airport traffic is light, ABC News reports. The decision is made by a supervisor. One factor enabling the move is that controllers can use different radio frequencies to communicate with pilots of planes and pilots of helicopters, per the Times. The two sets of pilots therefore may not be able to hear each other. The AP reports that staffing in the tower was a level considered normal and that the positions routinely are combined when a controller takes a break or a shift change is in progress. A supervisor made the change 40 minutes earlier than usual on Wednesday, per ABC. (More Potomac plane crash stories.)