A source tells NBC News that, according to a preliminary FAA report, a single air traffic controller was handling both planes and helicopters when the crash occurred. Normally at the D.C. tower at that time of day and for the volume of air traffic,

An air traffic control supervisor in the tower at Reagan Airport let a controller leave their shift early, a source familiar with the investigation confirmed to NBC News.

The San Carlos Airport (SQL) in San Mateo County will no longer have air traffic controllers starting in February following a dispute over pay, officials said.

After tense contract negotiations, a Bay Area airport narrowly avoided losing all of its air traffic controllers. The incident occurs in the wake of a tragic crash at Ronald Reagan National Airport, which a preliminary safety report about the collision from the Federal Aviation Administration suggests was caused by abnormal air traffic control tower staffing issues.