Narrative:

VFR WX, the first officer was flying on a vector for approach to land. ATIS was 'expect husky or bay visual approach, runway 16L/right, sea.' level at 4000 ft, 14 mi dogleg, 230 degree heading, and approach had not yet told us what runway to expect. However, first officer and I anticipated runway 16R. We set up the localizer for runway 16R, and just as we approached the extended ctrlines of runway 16L&right, approach cleared us for the visual runway 16L. First officer thought they said runway 16R and armed the localizer, but the autoplt didn't capture runway 16R localizer. I told ATC we were overshooting the final and first officer said, 'I thought we were cleared for runway 16R.' I said 'no, visual runway 16L,' then asked ATC to confirm approach clearance to runway 16L. ATC stated, 'cleared to runway 16L.' first officer quickly corrected and intercepted extended runway 16L centerline. Approach said, 'traffic 3 O'clock, 3000 ft, 2(?) mi.' I replied, 'searching.' approach then said, 'traffic, commuter, has you in sight, but might lose you.' on final now, slightly left of runway 16L centerline, approaching boeing field at FAF, and TCASII traffic showed several targets within 2 mi -- all below us. Then, TCASII 'monitor vertical speed' with a red square 300 ft below at 11 O'clock and less than a mi. First officer responded by leveling, and we noted that we might be too steep to continue the approach. TCASII 'climb, climb' -- target 6 O'clock, just below us. First officer climbed aircraft and said, 'I'm going around.' I radioed that we were on the go around. The target was then 5 O'clock, just below, and very close. On downwind, approach asked 'why did you go around?' I replied, 'TCASII RA.' approach: 'a false target from boeing field?' I answered, 'not sure.' it was not a false target. The commuter aircraft on visual to runway 16R either overshot his final or thought he was cleared runway 16L, because he was right below us on final to runway 16L. We were informed of this by a non revenue XXX captain in our aircraft after we landed.

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Original NASA ASRS Text

Title: AN MD80 FLC TOOK EVASIVE ACTION DURING A VISUAL APCH TO RWY 16L AT SEA, AFTER A TCASII RA DIRECTED THE FLC TO CLB. THE CREW RPTS THAT COMMUTER TFC WAS DIRECTLY BENEATH THEM, ON THE APCH FOR RWY 16L.

Narrative: VFR WX, THE FO WAS FLYING ON A VECTOR FOR APCH TO LAND. ATIS WAS 'EXPECT HUSKY OR BAY VISUAL APCH, RWY 16L/R, SEA.' LEVEL AT 4000 FT, 14 MI DOGLEG, 230 DEG HDG, AND APCH HAD NOT YET TOLD US WHAT RWY TO EXPECT. HOWEVER, FO AND I ANTICIPATED RWY 16R. WE SET UP THE LOC FOR RWY 16R, AND JUST AS WE APCHED THE EXTENDED CTRLINES OF RWY 16L&R, APCH CLRED US FOR THE VISUAL RWY 16L. FO THOUGHT THEY SAID RWY 16R AND ARMED THE LOC, BUT THE AUTOPLT DIDN'T CAPTURE RWY 16R LOC. I TOLD ATC WE WERE OVERSHOOTING THE FINAL AND FO SAID, 'I THOUGHT WE WERE CLRED FOR RWY 16R.' I SAID 'NO, VISUAL RWY 16L,' THEN ASKED ATC TO CONFIRM APCH CLRNC TO RWY 16L. ATC STATED, 'CLRED TO RWY 16L.' FO QUICKLY CORRECTED AND INTERCEPTED EXTENDED RWY 16L CTRLINE. APCH SAID, 'TFC 3 O'CLOCK, 3000 FT, 2(?) MI.' I REPLIED, 'SEARCHING.' APCH THEN SAID, 'TFC, COMMUTER, HAS YOU IN SIGHT, BUT MIGHT LOSE YOU.' ON FINAL NOW, SLIGHTLY L OF RWY 16L CTRLINE, APCHING BOEING FIELD AT FAF, AND TCASII TFC SHOWED SEVERAL TARGETS WITHIN 2 MI -- ALL BELOW US. THEN, TCASII 'MONITOR VERT SPD' WITH A RED SQUARE 300 FT BELOW AT 11 O'CLOCK AND LESS THAN A MI. FO RESPONDED BY LEVELING, AND WE NOTED THAT WE MIGHT BE TOO STEEP TO CONTINUE THE APCH. TCASII 'CLB, CLB' -- TARGET 6 O'CLOCK, JUST BELOW US. FO CLBED ACFT AND SAID, 'I'M GOING AROUND.' I RADIOED THAT WE WERE ON THE GAR. THE TARGET WAS THEN 5 O'CLOCK, JUST BELOW, AND VERY CLOSE. ON DOWNWIND, APCH ASKED 'WHY DID YOU GO AROUND?' I REPLIED, 'TCASII RA.' APCH: 'A FALSE TARGET FROM BOEING FIELD?' I ANSWERED, 'NOT SURE.' IT WAS NOT A FALSE TARGET. THE COMMUTER ACFT ON VISUAL TO RWY 16R EITHER OVERSHOT HIS FINAL OR THOUGHT HE WAS CLRED RWY 16L, BECAUSE HE WAS RIGHT BELOW US ON FINAL TO RWY 16L. WE WERE INFORMED OF THIS BY A NON REVENUE XXX CAPT IN OUR ACFT AFTER WE LANDED.

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.