Narrative:

We were being vectored for arrival in sfo for 28L. We had leveled off at 4000 ft and were asked to call visual on rj traffic that was at our 11 o'clock and descending to cross in front of us for runway 28R. We had visual on the traffic and then were given a turn to intercept 28L ATC asked if we had the field in sight. We responded that we had a visual on the field and visual on the traffic. ATC then cleared us for the visual 28L and said to maintain 180 knots to the bridge. We read back the clearance and put in 1800 ft in the altitude window. I clicked off the automation and started to descend and make a slow turn to intercept the runway centerline of 28L. Just as the descent was commenced we received a TCAS RA descend command. I started the descent and complied with the RA. I looked out my right window and saw the rj turning into us and descending so I kept the descent going and started a turn away. When the RA cleared we reestablished ourselves on the visual for 28L while keeping an eye on the rj (regional jet); who was still crowding us on our approach. No communication was received from tower of any potential conflict. Shortly after crossing the bridge we had another RA descend command from the same rj who was now over top of us and could not be seen. I complied with the RA and kept the speed up to try to get some separation horizontally as well until the RA cleared. Still no call from tower and we landed uneventfully. I have to believe that the rj never saw us and was lining up on the wrong runway. Or they were just very confused!

Related reports:

Google
 

Original NASA ASRS Text

Title: B737 flight crew reported receiving an RA from a nearby regional jet on parallel approaches to SFO Runways 28L and 28R.

Narrative: We were being vectored for arrival in SFO for 28L. We had leveled off at 4000 ft and were asked to call visual on RJ traffic that was at our 11 o'clock and descending to cross in front of us for RWY 28R. We had visual on the traffic and then were given a turn to intercept 28L ATC asked if we had the field in sight. We responded that we had a visual on the field and visual on the traffic. ATC then cleared us for the visual 28L and said to maintain 180 knots to the Bridge. We read back the clearance and put in 1800 ft in the altitude window. I clicked off the automation and started to descend and make a slow turn to intercept the runway centerline of 28L. Just as the descent was commenced we received a TCAS RA Descend command. I started the descent and complied with the RA. I looked out my right window and saw the RJ turning into us and descending so I kept the descent going and started a turn away. When the RA cleared we reestablished ourselves on the visual for 28L while keeping an eye on the RJ (Regional Jet); who was still crowding us on our approach. No communication was received from Tower of any potential conflict. Shortly after crossing the bridge we had another RA Descend command from the same RJ who was now over top of us and could not be seen. I complied with the RA and kept the speed up to try to get some separation horizontally as well until the RA cleared. Still no call from Tower and we landed uneventfully. I have to believe that the RJ never saw us and was lining up on the wrong runway. Or they were just very confused!

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.