A controller's error may have left two airplanes just 50 feet short of a collision at San Francisco International Airport about two weeks ago, federal investigators said Monday.
At about 1:30 p.m. on May 26, an air traffic controller cleared a SkyWest Airlines turboprop arriving from Modesto to land on Runway 28-Right, according to a preliminary report on the incident by the National Transportation Safety Board. Moments later, the same controller apparently forgot about the previous instruction and cleared a Republic Airlines regional jet departing for Los Angeles to take off from Runway 1-Left, which intersects 28-Right.
No damage or injury was reported.
The safety board announced Monday it is investigating the incident, officially termed a "runway incursion."
The incident also has been reviewed by the Federal Aviation Administration "since the second it occurred," FAA spokesman Ian Gregor said Tuesday.
"We have classified this preliminarily as controller error," Gregor said. "But we're continuing to investigate it."
According to the safety board's initial report, after the SkyWest turboprop, Flight 5741, touched down, the air traffic control tower's safety system -- known as the Airport Movement Area Safety System, or AMASS -- triggered an alert of a potential conflict.
The controller tried to instruct the SkyWest turboprop, an Embraer Brasilia, to stop, transmitting, "Uh, SkyWest hold! Hold! Hold!" over the radio.
The SkyWest crew hit the brakes, stopping in the middle of Runway 1-Left where it intersects with 28-Right.
Simultaneously, the Republic Airlines regional jet, an Embraer 170, was headed for takeoff. Realizing the aircraft was traveling too fast to stop, the captain proceeded with takeoff of the jet, Flight 4912, just over the halted SkyWest turboprop. The SkyWest crew guessed that the jet was just 30 to 50 feet above them, according to the report.
The Republic Airlines crew said that the distance between the two planes was more like 150 feet, but conceded that it was only a "guess," because they could not actually see the small turboprop beneath them.
In compiling its initial report, the safety board sent an investigator to San Francisco to collect radar data, record air traffic control communications, and take statements from flight crew and air traffic control personnel. The final investigation will take a year to 18 months to complete, a safety board spokesman said Tuesday.
The controller involved in the incident, according to the report, will be back on the job after decertification, mandatory additional training and recertification. The controller has been with the FAA since 1988 and at SFO since 1999.
SFO spokesman Mike McCarron had no comment on the incident or the investigation, stating that it was entirely under the FAA's purview.
Gregor, the FAA spokesman, emphasized that an incident of this gravity at SFO is rare.
"SFO does not have a history of serious runway incursions," Gregor said. "This is the first serious incursion this decade there."
According to the FAA, there have been 17 other runway incursions at SFO since 2001. Six have been caused by controllers, six by vehicle drivers and five by pilots.
All of them have been classified in the less serious categories of "C' and "D," meaning they posed no imminent threat of a crash. The FAA uses an A through D classification system for the severity of runway incursions, with A being the most serious.
The severity of the May 26 incident has yet to be classified.
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