The Federal Aviation Administration on Tuesday acknowledged that only one controller was in the tower, in violation of FAA policy, when a Comair jet crashed Sunday while trying to take off from the wrong runway in Lexington, Kentucky.
Forty-nine of 50 people aboard were killed.
The acknowledgment came after CNN obtained a November 2005 FAA memorandum spelling out staffing levels at the airport. The memo says two controllers are needed to perform two jobs -- monitoring air traffic on radar and performing other tower functions, such as communicating with taxiing aircraft.
In instances when two controllers are not available, the memo says, the radar monitoring function should be handed off to the FAA's Indianapolis Center.
The FAA confirmed to CNN on Tuesday that the lone controller was performing both functions Sunday at Blue Grass Airport in violation of the FAA policy.
The FAA should have scheduled a second controller for the overnight shift or should have shifted radar responsibilities to Indianapolis Center, FAA spokeswoman Laura Brown said.
Andrew Cantwell, regional vice president of the controller's union, had a mixed reaction to the announcement.
"I think it's a good thing that the FAA actually acknowledged that they were not following the guidance that they put out last year," he said, "but it's extremely sad that it takes an accident for that to become public knowledge."
Cantwell said he could not say with certainty whether additional staffing would have prevented Sunday's crash, but a second person would have allowed the controller to focus on operations.
Cantwell said controllers are not required to watch planes depart, and he does not think controller error contributed to the crash.
"I believe the controller performed his duties as required and, unfortunately, there were other duties to be accomplished at the same time," he said.
In addition to ground operations and monitoring the radar, the controller was responsible for supervisory duties, including paperwork, Cantwell said.
In a written statement released Tuesday evening, the FAA suggested that a second controller would not have prevented the accident.
"Had there been a second controller present on Sunday, that controller would have been responsible for separating airborne traffic with radar, not aircraft on the airport's runways," the statement said.
The FAA this week increased overnight staffing at Lexington as well as at airports in Duluth, Minnesota, and Savannah, Georgia, Cantwell said.
"It says to me that they're aware that a one-person (midnight shift) is not an adequate staffing," Cantwell said. "Unfortunately it takes an accident to make them come to their senses."
According to the FAA, the agency implemented the policy last year after a near in-air collision at Raleigh/Durham International Airport. At the time, only one controller was staffing the tower, sources told CNN.
After the incident, an FAA administrator ordered that the radar and tower functions be separated.
Comair Flight 5191, a Bombardier CRJ-200, crashed while trying to take off Sunday morning. The National Transportation Safety Board said the controller cleared the plane to take off from Runway 22, but the plane began its takeoff roll on Runway 26, a much shorter runway.
Pilots are required to read back to controllers their take-off clearances, which include the runway to be used.
Tire marks indicate the plane's wheels went into grass beyond the end of the runway. It became airborne after hitting an earthen berm, clipped a perimeter fence and hit a stand of trees before hitting the ground, said Debbie Hersman, who is heading up the NTSB's investigation.
The crash killed all 47 passengers and two of the three crew members onboard. The plane's first officer survived, but with critical injuries.