Aviation authorities in the United States are investigating whether an air traffic controller fell asleep at Reagan National Airport near Washington as two planes attempted to land.
One pilot says he made several attempts to contact the only controller on duty and had to abort his landing during final approach.
Both jets eventually landed safely with guidance from a controller more than 60km away.
The BBC reports efforts by other controllers elsewhere to reach the tower by telephone failed as well.
Aviation officials said the overnight shift at the airport was typically manned by a single controller.
In response, Transportation Secretary Ray LaHood said he had directed the FAA to put two controllers on the midnight shift at Reagan National Airport.
Former National Transportation Safety Board member John Goglia told the Associated Press the incident raised troubling concerns about air traffic controller fatigue.