On March 27, 2010, at 1112 Pacific daylight time, an operational error occurred at the San Francisco Airport Traffic Control Tower (SFO ATCT) when 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 300 feet vertically of each other over San Bruno, California. Both aircraft were under control of SFO ATCT at the time of the incident. The crew of UAL889 filed a near-midair collision report and a Traffic Alert and Collision Avoidance System (TCAS) report following the incident. There was no damage reported to either aircraft, and no injuries to passengers or crew.
According to a company report filed by the crew of UAL889, the SFO local controller cleared the flight for takeoff from runway 28L on the MOLEN 3 departure with clearance to climb to 3,000 mean sea level (msl). The flying First Officer reported after the landing gear was retracted at approximately the runway end, and at 1,100 msl, he heard the tower controller report traffic at 1 o’clock. This was followed immediately by the TCAS “TRAFFIC TRAFFIC” warning. According to the TCAS, the 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. Distance to the airplane described as slant range was 200-300 feet. The First Officer’s response was to push forward on the yoke to level the airplane. The other airplane disappeared from view through the 3 o’clock position. The First Officer then looked back into the cockpit at which time TCAS annunciated “ADJUST VERTICAL SPEED”, followed by a “DESCEND, DESCEND” command. The First Officer stated he complied with a push over to comply. The climb on MOLEN 3 was then continued.
History of Flight
N9870E was operating from the area of the city of San Francisco southbound along US 101, a freeway that passes just west of SFO. The pilot contacted the SFO local controller at 1809:34, reporting level at 1,600 feet. The controller instructed the pilot to, “…keep highway 101 off your left side,” and the pilot acknowledged. The route the pilot was following is a commonly used transition through the SFO class B surface area.
UAL889 was a scheduled 14 Code of Federal Regulations part 121 passenger flight operating from San Francisco, California, to Beijing, China. The pilot was instructed to taxi to runway 28L for departure. At 1810:10, the local controller cleared UAL889 into position and hold on the runway. At 1811:47, UAL889 was cleared for takeoff.
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 continued, “70E maintain visual separation pass behind that aircraft.” The pilot responded, “70E pass behind ’em.” At 1813:03, the controller transmitted, “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 continued, “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, “All right, trip…889’s going to uh departure,” and the controller acknowledged.
At 1815:23, the pilot of UAL889 recontacted SFO tower to request a discrete frequency to contact the tower on. The controller instructed the pilot to contact the tower on 128.65, and the pilot acknowledged.
At 1817:59, the controller-in-charge spoke with UAL889 on 128.65, advising the pilot, “…that was a VFR transition, and uh he was ahead and to your right, he had you in sight, he had visual, and he was instructed to pass behind you.” The pilot responded, “Well, his uh flight path was definitely gonna be uh converging with ours and uh there was uh less than uh 500 feet separation between the aircraft if you could uh pull the tapes and uh pull any you know uh radar sweeps we’d appreciate it.” The controller replied, “…understand – he did have visual with you. We’ll uh we’ll do that though, you can uh get that number from your ops if you want to call.” The pilot requested the number, and the controller again stated that they would need to get the number from UAL operations. The pilot acknowledged and the contact concluded.
The CIC logged the incident as a quality assurance review item in the Daily Record of Facility Operations. He also advised the front-line manager, who was out of the cab working on documentation of two previous incidents, of the United pilot’s complaint.
While still in flight, the captain of UAL889 recontacted the tower through UAL operations to discuss the incident further. The captain stated that she was very upset over the incident because of the close proximity of the Cessna, the lack of warning from the tower, and the TCAS alert indicating that the two aircraft were separated by only 200 feet vertically and horizontally. She questioned the tower’s procedures and the separation standards applicable to the encounter, and stated that she would be filing paperwork on the incident.
SFO ATCT did not initially file an operational error report on the incident. After review by service area and FAA headquarters management, the facility was directed to file an operational error report based on non-compliance with paragraph 7-2-1 of FAA Order 7110.65, and did so on April 5, 2010.
Radar data for this report was obtained from the ASR-9 sensor located at Oakland, California, about 8 miles northeast of SFO. Two graphics showing an overview of the paths of the two aircraft and a close view of their minimum separation, have been entered in the docket. 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 between UAL889 and N9870E of about 600 feet.
The local controller was assigned to SFO ATCT in 1999 and was qualified on all control positions in the tower.
Asked about any unusual circumstances on the day of the incident, the local controller noted that he had been controller-in-charge earlier that morning when another controller had an operational error. Reporting of that incident and the associated paperwork required the attention of the front-line manager (supervisor) on duty and resulted in the supervisor being occupied with administrative duties outside the tower cab for almost the whole shift. That effectively reduced available staffing because the controllers then had to fill the CIC position as well as the control positions.
Just before the incident, the radar coordinator asked the local controller if she should accept a handoff from Northern California TRACON on Cessna N9870E. As UAL889 was the only runway 28 departure pending, he told her to take the handoff. The Cessna reported over Hunter’s Point (north of the airport), and the local controller instructed the pilot to keep highway 101 off of his left side as he proceeded southbound. The ground control position then began verbally coordinating with the radar coordinator regarding an aircraft that would be taxiing around the west end of runways 28L/R “after the guy on the runway.” (UAL889) Ground control then amended the request to cross two aircraft instead of one. The local controller looked at the west end taxiway to check on the positions of the crossing aircraft and then cleared UAL889 for takeoff. He then looked back at taxiway Z to make sure that the taxiing aircraft were holding short of the runways while UAL889 departed. The local controller then looked at the radar display and realized there was a conflict between N9870E and UAL889. He pointed out the departing United aircraft as traffic to the Cessna pilot and instructed him to pass behind it.
When interviewed, the local controller stated that after he recognized the conflict and told the Cessna to turn behind the departure, he believed that he had successfully resolved the problem. When the crew of UAL889 requested another frequency to talk to the tower on, the local controller advised the CIC that the pilot was upset about the transition traffic, they had gotten “too close,” and the pilot wanted to talk to someone about it. The crew was given a spare frequency to use, and did contact the CIC to ask about the incident.
The local controller stated that his normal scan when clearing an aircraft for takeoff is to scan the runway, check the radar display, then go back to the runway. He said that in this instance, he was distracted by the ground controller’s taxi coordination and missed checking the radar display until after the departure was rolling.
The local controller stated that the tower has a procedure for using a flight strip as a reminder that there are aircraft on the transition route. It is his normal practice to physically place the reminder strip on top of the flight strips for runway 28 departures, but in this case he did not use his normal procedure and he was not sure exactly where he placed the strip.
The radar coordinator was assigned to SFO ATCT on November 23, 2008. She was still in training, and was certified on all positions except local control and cab coordinator.
She described the duties of the radar coordinator as coordinating with NCT, coordinating with the ground control position about the use of taxiway Z at the west end of runways 28L/R, serving as a second set of eyes for local control, taking handoffs, scanning strips, and updating proposed departure times to prevent flight plan timeouts.
The radar coordinator had been on position about two minutes at the time of the incident. She was engaged in coordinating a request from ground control to cross the west end of runways 28 with one or two aircraft. It was an extended exchange, and somewhat confusing because there was training in progress at GC. The trainee asked for one thing, and then the instructor changed it. The coordination was done verbally directly between the radar coordinator and the ground controllers, not on the interphone, so it was all audible to the local controller and may have momentarily distracted him. When the coordination with GC concluded, the radar coordinator reported hearing the local controller instructing N9870E to “…pass behind…” someone. She looked at the radar display and recognized the conflict. UAL889 had just acquired a radar tag after departure. With the training in progress and other activity in the cab, she stated that, “…it was pretty loud up there.”
When the radar coordinator took over the position, she did receive a recorded position relief briefing that included information on the Cessna, but she did not recall exactly what was said. Transition traffic is a normal part of the relief briefing, and she was aware of the Cessna when she took over the position. She last remembers seeing the aircraft “…pretty far north” in the tower’s airspace, maybe near the Hunter’s Point area or Candlestick Park.
The controller-in-charge was assigned to SFO ATCT in 1991, and was qualified on all positions in the tower cab. When interviewed, he described the CIC’s duties as “…answer the phones, watch the operation, deal with breaks, and perform other administrative duties.”
Around the time of the incident, the CIC was essentially occupied with administrative duties, and was not monitoring the operation. There is no local requirement for the CIC to directly monitor control positions. The CIC first became aware of the incident shortly after UAL889 departed, when the local controller told him that the pilot would be calling on frequency 128.65 about a Cessna. The CIC looked at the radar display and saw the Cessna about halfway between SFO and San Carlos. UAL889 was off the edge of the radar display by then.
The pilot of UAL889 did call on the spare frequency to request information on the incident. During that discussion, the CIC asked the local controller if traffic had been issued, if the Cessna had the B777 in sight, and if visual separation had been applied. The local controller responded affirmatively to all three questions. The CIC advised the pilot of that information, and the conversation concluded.
Post-Incident Corrective Actions
After this incident, SFO ATCT management and controllers initiated a review of the event and the circumstances leading up to it. The following actions were taken:
- The supervisor on duty on the day of the incident conducted a Quality Assurance Review, examining radio and radar recordings, interviewing the local controller involved, and identifying opportunities for improvements.
- The Air Traffic Manager discussed the incident with both pilots via telephone, and met with the captain of UAL889 at the tower.
- The facility produced a “Summary Report” of the incident, itemizing the existing SFO ATCT procedures that should have prevented it – including the ability to exercise more control over transitions, assistance to the local controller by the radar coordinator, use of memory aids, direct supervisor or CIC monitoring of the local control position, and better control over the timing of runway 28 takeoff clearances vs. transitioning aircraft.
SFO ATCT also implemented short-term followup actions, including:
- Face-to-face supervisory briefings on new mandatory procedures for increasing awareness of runway 28 departures, including verbal announcements in the tower cab, mandatory use of memory aids, and focus on the radar coordinator’s responsibility to assist the local controller.
- Team briefings on this and similar past incidents, including a replay of the UAL889 event.
- A Safety Risk Analysis panel that included an open discussion between management and controllers on all aspects of the UAL889 event and possible corrective or mitigating actions.
- Issuance of an Operational Notice revising coordination and control procedures for VFR transition traffic through the SFO class B surface area.
- Establishing a panel to review and discuss the current transition corridor, including representatives from the tower, SFO Airport, FAA Flight Standards, Northern California TRACON, Air Transport Association, the Aircraft Owners and Pilots Association, and the National Air Traffic Controllers Association.
- Coordinating with other FAA facilities having a stand-alone class B airspace position, such as LaGuardia and Newark, to discuss such operations and determine whether such a position would be beneficial at SFO.