An air traffic supervisor at Ronald Reagan Washington National Airport allowed one controller to leave work early Wednesday night, shortly before 67 people were killed in a midair collision between a commercial jet and a military helicopter near the nation’s capital.

The supervisor at the airport’s control tower left one person to handle both helicopter and plane traffic around one of the busiest runways in the country, according to multiple outlets. 

Usually one controller advises helicopters flying in the area while the other talks with passenger jet pilots coming in and out of the airport, which sits along the western bank of the Potomac River. 

The National Transportation Safety Board, which is investigating the worst domestic aviation incident in a generation, said it is looking to determine if the Army Black Hawk pilot was flying too high at the time of the crash. 

The Federal Aviation Administration shut down parts of the airspace for helicopters Friday as the search continues for the Army helicopter’s black box. 

Federal authorities are currently reviewing two black boxes recovered Thursday night from the wreckage of the American Airlines flight arriving from Wichita, Kansas.  

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As of Friday, D.C. Fire and EMS said 41 victims have been pulled from the watery wreckage. The remains of four additional victims are accounted for, but are still inside the plane, according to CNN. 

Children as young as 11, union laborers and foreign nationals from the Philippines and China all died when the plane went down just before 9 p.m. Wednesday.

• Matt Delaney can be reached at mdelaney@washingtontimes.com.