An air traffic controller at Ronald Reagan Washington National Airport fell asleep on duty early Wednesday morning, leaving the control tower silent and forcing pilots of two commercial planes to land on their own, the National Transportation Safety Board said today.
The controller, who had 20 years of experience, including 17 at Reagan National, was suspended earlier Thursday by the Federal Aviation Administration while its investigation proceeds.
The NTSB report, which does not name the controller, said he had been working his fourth consecutive overnight shift, which runs from 10 p.m. to 6 a.m., and that "human fatigue issues are one of the areas being investigated."
"I am determined to get to the bottom of this situation for the safety of the traveling public," FAA Administrator Randy Babbitt said in a statement announcing the controller's suspension.
"As a former airline pilot, I am personally outraged that this controller did not meet his responsibility to help land these two airplanes," he said. "Fortunately, at no point was either plane out of radar contact and our back-up system kicked in to ensure the safe landing of both airplanes."
Pilots of an American Airlines and United Airlines plane each said they had been in contact with regional air traffic controllers before being handed off to the Reagan National tower for approach and landing.
But as the planes radioed their requests to land in the nation's capital early Wednesday morning, all they heard was silence.
"American 1900, just so you're aware the tower is apparently not manned," a regional controller told the pilots of one plane, according to radio recordings obtained by ABC News. "So you can expect to go in as an uncontrolled airport."
The pilot executed an airport flyover -- routine aviation procedure -- before landing on his own without help from the ground.
Fifteen minutes later, United flight 628 from Chicago also was unable to contact the Reagan tower.
"The aircraft went in just as an uncontrolled airport," one regional controller said on the recording. "It's happened before though."
The United pilot also treated the airport as unmanned and landed safely.
Federal transportation officials are now conducting a comprehensive review air traffic controller staffing at airports across the country.
While Reagan National is staffed with multiple air traffic controllers during the day, the overnight shift is managed by just one controller because there are no departures overnight and few arrivals.
But midnight shifts at other major U.S. airports, including New York's John F. Kennedy and LaGuardia, Chicago O'Hare and Boston Logan, all have two controllers on duty.
Richmond, Va., and Andrews Air Force Base are two regional airports that only have one controller in the tower for the midnight shift.
"The reality is that we should probably never have just one controller at a major airport anytime, anywhere," said aviation expert John Nance. "But the fact that it's Washington, D.C., obviously accelerates the questions like this."
Transportation Secretary Ray LaHood took the unusual step late Wednesday of immediately ordering a second air traffic controller at Reagan National Airport on the midnight shift.
"It is not acceptable to have just one controller in the tower managing air traffic in this critical air space," LaHood said in a statement. "I have also asked FAA Administrator Randy Babbitt to study staffing levels at other airports around the country."
One veteran air traffic controller contacted by ABC News said the incident would not have presented a danger to passengers, because pilots are trained to land without air traffic control. But he added that it was highly unusual.
"It's a big deal when two aircraft at Washington National Airport are not able to contact the tower," said Dick Marakovitz, a controller for 27 years. "That's a big deal."
American Airlines Flight 1012, a Boeing 737, had 91 passengers and six crew members on board. United Airlines Flight 628, an Airbus A320, had 63 passengers and five crew members.
Reagan National Airport serves some 18 million passengers a year.
ABC News' Devin Dwyer contributed to this report.