The tower controller tells pilots among other things, what runway to use and if they are cleared for landing. But that did not happen at Reagan National Airport on Tuesday night.
The planes - an American Airlines flight from Dallas and a United Airlines flight from Chicago with a combined 165 people on board - landed safely.
"The captain comes on the speaker phone and says, 'You won't believe this, but we can't get in contact with tower control. We don't have any clearance,'" said Medardo Rincon, a passenger on one of those flights. "I blame whoever puts one person in tower control at 12 midnight with no air traffic, they're probably bored, they're probably sleepy, I mean, you're over the capitol."
About 30 other airports around the country also have a single controller on duty on the overnight shift. In some instances, the controllers work alone for only a part of the shift.
The FAA is examining whether staffing on those overnight shifts should be increased. San Diego International Airport and Sacramento International Airport are on that list.
Also, the FAA is requiring regional facilities to contact local airport towers to ensure that a controller is available to land a plane. If contact cannot be made, the regional facility has to give the pilot the option to fly to another airport.
The controller on duty in the tower, veteran air traffic supervisor Dan Creedon, acknowledged to investigators who interviewed him Thursday that he had dozed off, the National Transportation Safety Board said. Creedon was working his fourth 10 p.m. to 6 a.m. shift in a row, according the board, which is investigating the episode.
Immediately after the incident, Transportation Secretary Ray LaHood 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 reason you need two people in the tower is if you have an emergency. Because No. 1, you've got one controller then who could handle that emergency, deal directly with the airplane, and find out all the details of the emergency," explained Bob Richards, a former air traffic controller. "The second person you would have would be coordinating the emergency, calling out the ground equipment, calling out the airlines, calling out other traffic facilities, whatever needs to be done. Simply having one person do that is not a good thing."
On Friday, the NTSB recommended to the FAA to no longer allow air traffic controllers to provide supervisory oversight while performing operational air traffic duties. The recommendation wasn't directly related to this week's incident. But if the FAA were to follow the board's recommendation, the agency would effectively have to assign at least two people - a supervisor and a controller - to every shift.
In the incident at Reagan National Airport, aviation experts say the real safety threat was not actually in the air, but on the ground where maintenance or other equipment could have been on the runways.
The incident has renewed concern about the potential safety consequences of controllers suffering from fatigue, a longstanding concern of the board.
It has also sparked criticism of FAA's practice of scheduling a single controller on overnight shifts at some airports, but especially at Reagan, which is in Arlington, Va., and just across the Potomac River from downtown Washington.
"This is not a mom-and-pop airport for small planes, and is in the vicinity of some very sensitive airspace," said Rory Kay, a former Air Line Pilots Association safety chairman and an international airline captain.
At least one congressional committee has launched its own investigation, and the issue is expected to be raised next week when the House takes up a bill to provide long term authority for FAA programs.
The Associated Press contributed to this story.