Narrative:

While being vectored for an approach to sea (runway 16 in use), we were given a descent to 5000 ft on an east downwind, nwbound. It was nighttime, VMC. Traffic volume was moderate to heavy. I was the captain, and also the PF. The first officer read back the new altitude clearance to ATC. We used SOP to set and confirm the new altitude, and I began a descent at about 1000 FPM. As we descended through 6000 ft, I commented that there was traffic at our 1-2 O'clock position, swbound towards our position. He appeared to be at, or near, our altitude. The first officer acknowledged seeing the traffic and possible conflict. Shortly thereafter, we received a TCASII RA on that traffic. About that time, sea approach told air carrier Y, an A320, to expedite his descent. At this point we received a TCASII RA to descend. I disconnected the autoplt and autothrottle, and used SOP to follow the RA guidance. The ATC controller made a comment to us regarding the traffic, and the first officer radioed that we were responding to a TCASII RA. At this point, both aircraft appeared to be continuing a descent towards each other. Our TCASII 'descend' RA then changed to a 'climb' RA. I followed the guidance, and the RA shortly thereafter terminated. During this time the first officer had the other aircraft in sight and watched it pass off our right, below our flight path. Nothing else was said to, or by, the ATC controller regarding this issue. We completed a normal arrival and visual approach without further incident. From our point of view, it appears ATC had 2 aircraft on descending vectors towards each other, both assigned the same altitude (5000 ft). After landing we talked (via radio) to the air carrier Y crew. They commented that they, also, had responded to two, opposite direction TCASII RA's. Dispatch was notified by phone after landing.

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Original NASA ASRS Text

Title: B737 FLT CREW LNDG SEA EXPERIENCED TCASII RA WITH A320 ON BASE TURN AS BOTH ACFT ARE CLRED TO 5000 FT.

Narrative: WHILE BEING VECTORED FOR AN APCH TO SEA (RWY 16 IN USE), WE WERE GIVEN A DSCNT TO 5000 FT ON AN E DOWNWIND, NWBOUND. IT WAS NIGHTTIME, VMC. TFC VOLUME WAS MODERATE TO HVY. I WAS THE CAPT, AND ALSO THE PF. THE FO READ BACK THE NEW ALT CLRNC TO ATC. WE USED SOP TO SET AND CONFIRM THE NEW ALT, AND I BEGAN A DSCNT AT ABOUT 1000 FPM. AS WE DSNDED THROUGH 6000 FT, I COMMENTED THAT THERE WAS TFC AT OUR 1-2 O'CLOCK POS, SWBOUND TOWARDS OUR POS. HE APPEARED TO BE AT, OR NEAR, OUR ALT. THE FO ACKNOWLEDGED SEEING THE TFC AND POSSIBLE CONFLICT. SHORTLY THEREAFTER, WE RECEIVED A TCASII RA ON THAT TFC. ABOUT THAT TIME, SEA APCH TOLD ACR Y, AN A320, TO EXPEDITE HIS DSCNT. AT THIS POINT WE RECEIVED A TCASII RA TO DSND. I DISCONNECTED THE AUTOPLT AND AUTOTHROTTLE, AND USED SOP TO FOLLOW THE RA GUIDANCE. THE ATC CTLR MADE A COMMENT TO US REGARDING THE TFC, AND THE FO RADIOED THAT WE WERE RESPONDING TO A TCASII RA. AT THIS POINT, BOTH ACFT APPEARED TO BE CONTINUING A DSCNT TOWARDS EACH OTHER. OUR TCASII 'DSND' RA THEN CHANGED TO A 'CLB' RA. I FOLLOWED THE GUIDANCE, AND THE RA SHORTLY THEREAFTER TERMINATED. DURING THIS TIME THE FO HAD THE OTHER ACFT IN SIGHT AND WATCHED IT PASS OFF OUR R, BELOW OUR FLT PATH. NOTHING ELSE WAS SAID TO, OR BY, THE ATC CTLR REGARDING THIS ISSUE. WE COMPLETED A NORMAL ARR AND VISUAL APCH WITHOUT FURTHER INCIDENT. FROM OUR POINT OF VIEW, IT APPEARS ATC HAD 2 ACFT ON DSNDING VECTORS TOWARDS EACH OTHER, BOTH ASSIGNED THE SAME ALT (5000 FT). AFTER LNDG WE TALKED (VIA RADIO) TO THE ACR Y CREW. THEY COMMENTED THAT THEY, ALSO, HAD RESPONDED TO TWO, OPPOSITE DIRECTION TCASII RA'S. DISPATCH WAS NOTIFIED BY PHONE AFTER LNDG.

Data retrieved from NASA's ASRS site as of July 2007 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.