As a result, a single controller was monitoring both the airplanes and the helicopters flying in the area, a source familiar with the investigation told NBC News.
One controller is typically in charge of helicopters while another watches over airplanes. The FAA said Thursday that one air traffic controller was doing the job of two people at the time of the devastating crash.
According to radio transmissions from Wednesday night, the lone controller warned the US Army Black Hawk that it was getting too close to the American Airlines passenger flight, which the experienced helicopter pilot acknowledged.
Experts believe the helicopter pilot may have maneuvered to avoid the wrong plane — a jet of the same model that was taking off farther away — and never saw the American Airlines flight until it was too late.
The National Transportation Safety Board is also investigating whether the chopper was flying too high.