Date: 201503
Local time of day: 1201-1800
Location: SFO.Airport, CA
Flight conditions: VMC
Weather elements / visibility: 10
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B SFO
ATC / advisory: Tower SFO
Second aircraft: B757 Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Human factors: Situational Awareness
Second reporter function: Captain; Pilot Flying
Anomaly: Conflict Airborne Conflict
Detector: Automation Aircraft RA; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Vectors to the visual approach 28L SFO; with the captain flying the approach and myself as PM. We reported B757 in sight; who was for the right (28R). We were instructed at first to maintain 180 knots and immediately slowed to comply. We were not cleared for a visual approach until after we were vectored on a dog leg for final; where we used the ILS for lateral and vertical guidance. Shortly after joining final we were instructed to slow to 170 knots until 6 DME; as the B757 was not very far ahead of us. As the two airplanes progressed; and with myself primarily concerned with the traffic (90 percent outside); I noticed the B757 level off; or even pitch slightly up; drop their gear and obviously configure for approach. I also noticed that the B757 speed was decreasing and informed the captain; where we selected landing flaps 25 and slowed to approach speed (145 kts) so as not to pass the traffic. With eyes glued to the B757; that aircraft trend was slowly but consistently trending toward our flight vector. I glanced inside and noted that the captain was even slightly left of course; confirming that we were not the migrating culprits. The lateral closure between our two airplanes was slow but consistent; and just as the proximity was becoming uncomfortable the B757 self-initiated a go around; and seconds later we got an RA to descend. No maneuvering was required on our part as the RA pitch bar did not command action beyond our normal glide path gradient at the time. From my vantage point it appeared that the B757 vector was still migrating toward our path even after initiating the go around; and perhaps 2-4 seconds passed before the B757 noticeably turned to the right; away from our vector. We continued to a normal landing with no need at any time to execute an avoidance maneuver beyond ensuring our descent complied with the RA. Whatever was going on in the B757 cockpit; I applaud them in their decision to initiate a go around before things 'got out of hand' to the point where we would need to take more urgent action to avoid a collision.


Second narrative: While being vectored to a visual approach to Runway 28L in SFO; we were initially on autopilot. A B757 was also being vectored to runway 28R at the same time. Eventually we were cleared the visual; and on autopilot; intercepted the final approach and glide slope. We were also given the restriction to slow to 170 knots until 6 miles; which we did. Approaching the 'bridge'; I disconnected the autopilot and began to hand fly as we were on speed; on glide slope; and on the localizer as well. We were told to not pass the B757; but the B757 appeared to suddenly slow so we began slowing below 170 knots to stay behind him; in fact went to 30 flaps and 30 approach speed to stay behind him. That flight began to look like they were getting left of their centerline; so we creeped to the left a little to give him some room. Then we got a TCAS RA alert to descend so I continued to descend on the glide slope and stay just at the bottom of the red TCAS alert bar. The B757 went around; appeared to go over the top of us somewhat; but separation was assured and the RA alert stopped. We continued and made an uneventful landing. During the entire event we had the B757 insight.


Synopsis: B777 flight crew on visual approach to Runway 28L at SFO experiences a TCAS RA with a B757 on approach to Runway 28R. The B757 had drifted slightly left of course and was slightly high and initiated a go around at the same time the B777 crew received their RA.