Narrative:

On approach to runway 34R at sea. I was cleared visibility approach to follow an air carrier widebody transport at 12 O'clock and 4 mi. I overheard the controller clear another air carrier, large transport Y, for a visibility 34L and to maintain a visibility on me. Moments later the traffic alert system activated, warning of traffic from behind us and 200', going to 100' above. The rfd warning traffic symbol on our scope was rapidly overtaking us and showed traffic directly overhead. We were already descending 1700 FPM and the RA was recommending 2000 FPM. I questioned the approach controller about the traffic as we increased descent rate and he responded with, 'he is maintaining visibility sep on you--he is landing 34L. You are cleared for 34R. Contact the tower.' at about this time I became aware of a dark shadow overheard. I looked up out the left eyebrow window, which was filled with large transport Y. He passed no more than 50-75' overhead, and then as we made a shallow turn to the right he passed in front of us. At no time were we to the left of the 34R localizer centerline. I asked the controller how large transport Y was maintaining a visibility sep from us, as he was now completely in front of us and I could not see any part of his cockpit. The response was unsatisfactory and we changed over to the tower frequency. Air carrier large transport Y subsequently reduced his speed and we touched down almost simultaneously. All s-turning we made to maintain our sep on the widebody transport ahead were made to the east of 3 yr. I believe the TCAS saved our lives and in retrospect I wish I had followed its advisories more aggressively.

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Original NASA ASRS Text

Title: NMAC BETWEEN 2 ACR LGT'S ON PARALLEL VISUAL APCHS TO SEA.

Narrative: ON APCH TO RWY 34R AT SEA. I WAS CLRED VIS APCH TO FOLLOW AN ACR WDB AT 12 O'CLOCK AND 4 MI. I OVERHEARD THE CTLR CLR ANOTHER ACR, LGT Y, FOR A VIS 34L AND TO MAINTAIN A VIS ON ME. MOMENTS LATER THE TFC ALERT SYS ACTIVATED, WARNING OF TFC FROM BEHIND US AND 200', GOING TO 100' ABOVE. THE RFD WARNING TFC SYMBOL ON OUR SCOPE WAS RAPIDLY OVERTAKING US AND SHOWED TFC DIRECTLY OVERHEAD. WE WERE ALREADY DSNDING 1700 FPM AND THE RA WAS RECOMMENDING 2000 FPM. I QUESTIONED THE APCH CTLR ABOUT THE TFC AS WE INCREASED DSNT RATE AND HE RESPONDED WITH, 'HE IS MAINTAINING VIS SEP ON YOU--HE IS LNDG 34L. YOU ARE CLRED FOR 34R. CONTACT THE TWR.' AT ABOUT THIS TIME I BECAME AWARE OF A DARK SHADOW OVERHEARD. I LOOKED UP OUT THE LEFT EYEBROW WINDOW, WHICH WAS FILLED WITH LGT Y. HE PASSED NO MORE THAN 50-75' OVERHEAD, AND THEN AS WE MADE A SHALLOW TURN TO THE RIGHT HE PASSED IN FRONT OF US. AT NO TIME WERE WE TO THE LEFT OF THE 34R LOC CENTERLINE. I ASKED THE CTLR HOW LGT Y WAS MAINTAINING A VIS SEP FROM US, AS HE WAS NOW COMPLETELY IN FRONT OF US AND I COULD NOT SEE ANY PART OF HIS COCKPIT. THE RESPONSE WAS UNSATISFACTORY AND WE CHANGED OVER TO THE TWR FREQ. ACR LGT Y SUBSEQUENTLY REDUCED HIS SPD AND WE TOUCHED DOWN ALMOST SIMULTANEOUSLY. ALL S-TURNING WE MADE TO MAINTAIN OUR SEP ON THE WDB AHEAD WERE MADE TO THE E OF 3 YR. I BELIEVE THE TCAS SAVED OUR LIVES AND IN RETROSPECT I WISH I HAD FOLLOWED ITS ADVISORIES MORE AGGRESSIVELY.

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.