An air traffic controller who was unavailable to help two jets land at a busy Washington DC airport has been suspended, an official has said.
The planes landed safely, despite being unable to make contact with the control tower early on Wednesday.
The lone nighttime controller at Reagan National Airport had fallen asleep, the Associated Press reported.
In response, regulators have ordered that two controllers be on duty on the midnight shift.
The jets carried a total of 165 people.
The FAA has launched a national inquiry into tower staffing, officials said.
Aviation officials told media the overnight shift at the airport was typically manned by a single controller.
The jet pilots were unable to raise the airport control tower on the radio as they approached to land. The efforts of other controllers elsewhere to reach the tower by telephone failed as well.
US Transportation Secretary Ray LaHood said that in response he had directed the FAA to put two controllers on the midnight shift at Reagan National Airport.