US aviation officials are boosting air traffic control staffing at a busy Washington DC airport after two jets were 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.
The jets carrying a total of 165 people landed safely without tower help.
The Federal Aviation Administration (FAA) has launched a national inquiry into tower staffing, officials said.
Aviation officials told US 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.
http://www.bbc.co.uk/news/world-us-canada-12850844
Note: 24 March 2011 Last updated at 14:27 GMT