At about midnight Tuesday, two passenger jets were forced to land at Reagan National Airport without any help from the lone controller on duty. Both jets arrived safely.
The controller said it was his fourth consecutive overnight shift, and he had trouble staying awake.
Now, Transportation Secretary Ray LaHood has ordered a review of controller staffing at airports across the nation and directed that two controllers staff the midnight shift at Reagan from now on.
The incident comes nearly five years after a fatal crash in Kentucky in which a controller was working alone. Accident investigators said that controller was most likely suffering from fatigue, although they placed responsibility for the crash that took 49 lives on the pilots.
The National Air Traffic Controllers Association warned at the time against putting controllers alone on shifts and assigning tiring work schedules.
The union's president, Paul Rinaldi, made the same point again on Thursday: "One-person shifts are unsafe. Period."
The Associated Press contributed to this story.