Incident Overview
On March 27, 2010, at 1112 Pacific daylight time, an operational error occurred at the San Francisco Airport Traffic Control Tower (SFO ATCT). United Airlines flight 889 (UAL889), a Boeing 777 en route from San Francisco, California to Beijing, China, and N9870E, a Cessna 182 transiting the SFO class B surface area southbound toward Palo Alto, California, passed within approximately 480 feet laterally and 350 feet vertically of each other over San Bruno, California. Both aircraft were under the control of SFO ATCT at the time. The crew of UAL889 filed a near-midair collision report and a Traffic Alert and Collision Avoidance System (TCAS) report. No damage was reported to either aircraft, and no injuries occurred to passengers or crew.
Sequence of Events
UAL889 was cleared for takeoff from runway 28L on the MOLEN 3 departure with a clearance to climb to 3,000 feet mean sea level (msl). The flying first officer reported that after landing gear retraction at about the runway end and at 1,100 msl, he heard the tower controller report traffic at 1 o'clock. This was immediately followed by a TCAS "TRAFFIC TRAFFIC" warning. The TCAS target was at 1,400 msl. The pilots visually acquired a light high-wing airplane in a hard left turn at their 1 o'clock position. Both crew members reported seeing only the underside of the airplane. The distance to the airplane, described as slant range, was 200-300 feet. The first officer pushed forward on the yoke to level the airplane. The other airplane disappeared from view through the 3 o'clock position. The first officer then heard TCAS annunciate "ADJUST VERTICAL SPEED," followed by a "DESCEND, DESCEND" command, and complied. The climb on the MOLEN 3 departure was then continued.
N9870E was operating from the area of San Francisco southbound along US 101. The pilot contacted SFO local controller at 1809:34, reporting level at 1,600 feet. The controller instructed the pilot to keep highway 101 off his left side, which the pilot acknowledged. This route is commonly used for transitioning through the SFO class B surface area.
At 1812:50, the local controller transmitted, "70 echo traffic off the departure end climbing out of 500 heavy triple 7." The pilot of N9870E responded, "70E in sight." The controller then said, "70E maintain visual separation pass behind that aircraft." The pilot responded, "70E pass behind 'em." At 1813:03, the controller transmitted to UAL889, "United 889 heavy traffic's uh just ahead and to your right has you in sight Cessna 1,500 they're maintaining visual separation." At 1813:13, the controller added, "United 889 heavy traffic's no factor contact Norcal departure." The pilot of UAL889 responded, "OK, that set off the TCAS...that was...that...we need to talk."
At 1813:47, UAL889 transmitted to departure. At 1815:23, the pilot recontacted SFO tower to request a discrete frequency. The controller instructed the pilot to contact the tower on 128.65. At 1817:59, the controller-in-charge (CIC) spoke with UAL889 on 128.65, advising the pilot that the VFR transition had visual and was instructed to pass behind. The pilot requested that tapes and radar sweeps be pulled. The CIC agreed but advised the pilot to obtain a number from UAL operations.
Radar Data
Radar data from the ASR-9 sensor at Oakland, California, about 8 miles northeast of SFO, showed the paths of the two aircraft. The applicable separation standard between VFR and IFR aircraft in class B airspace is either 1.5 miles laterally or 500 feet vertically. At closest point of approach, the aircraft were separated by about 480 feet laterally and 350 feet vertically, resulting in a minimum slant range distance of about 600 feet.
Personnel Actions
The local controller, assigned to SFO ATCT in 1999 and qualified on all positions, stated that he had been distracted by ground controller's taxi coordination and missed checking the radar display until after departure was rolling. He also did not use his normal procedure of placing a reminder strip for transition traffic. The radar coordinator, in training and on position for about two minutes, was engaged in coordinating requests from ground control. The CIC was occupied with administrative duties and was not monitoring the operation. The CIC first became aware of the incident after UAL889 departed, when the local controller informed him about the pilot's call.
Post-Incident Actions
After the incident, SFO ATCT management and controllers initiated a review. The supervisor on duty conducted a Quality Assurance Review. The Air Traffic Manager discussed the incident with both pilots. The facility produced a "Summary Report" identifying procedures that should have prevented the incident. Short-term follow-up actions included face-to-face supervisory briefings, team briefings, a Safety Risk Analysis panel, issuance of an Operational Notice revising procedures for VFR transition traffic, and establishing a panel to review the transition corridor with representatives from various organizations. The facility was directed to file an operational error report on April 5, 2010, based on non-compliance with paragraph 7-2-1 of FAA Order 7110.65.