Narrative:

Wind was 190-200 degrees at 20-25 KTS. We were descending on the runway 25L localizer. Approach offered runway 19L due to wind. We accepted the offer. About 10-15 NM from las, controller began to vector us, and shortly slowed us to 170 KTS. As we were vectored to the left base, I noticed a twin otter low and below us on the approximately same heading. I shortly lost sight of the otter below. Controller step-descended us above the otter. The controller called the position of the otter as 1 - 2 O'clock at 3500 ft. We did not report it in sight at that time. We were close in and high. Finally, the controller told us to join the final on the assigned heading (270 degrees, I think) and maintain 4000 ft MSL (until on final, cleared visual approach) due to wbound otter at 3500 ft below. I complied. We were somewhat high, so I started idle descent as soon as I turned final. TCASII immediately gave us an RA to pull up on climb. I did not comply with the TCASII RA because the otter position calls had been north of us and the otter had reported us in sight and had been told to maintain visual separation. Nothing was said on the radio by anyone. After landing, my first officer said he thought I should have complied with the RA. In hindsight, he was right. What if the RA had been from one of the many helicopters or another aircraft in the area? A go around would have been better than any risk of collision.

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Original NASA ASRS Text

Title: B738 PIC DISREGARDS TCASII RA FROM A DHC6 ON PARALLEL RWY 19 APCH AT LAS BECAUSE OF SEQUENCING BY L30. AFTER LNDG, FO QUESTIONS CAPT'S JUDGEMENT.

Narrative: WIND WAS 190-200 DEGS AT 20-25 KTS. WE WERE DSNDING ON THE RWY 25L LOC. APCH OFFERED RWY 19L DUE TO WIND. WE ACCEPTED THE OFFER. ABOUT 10-15 NM FROM LAS, CTLR BEGAN TO VECTOR US, AND SHORTLY SLOWED US TO 170 KTS. AS WE WERE VECTORED TO THE L BASE, I NOTICED A TWIN OTTER LOW AND BELOW US ON THE APPROX SAME HDG. I SHORTLY LOST SIGHT OF THE OTTER BELOW. CTLR STEP-DSNDED US ABOVE THE OTTER. THE CTLR CALLED THE POS OF THE OTTER AS 1 - 2 O'CLOCK AT 3500 FT. WE DID NOT RPT IT IN SIGHT AT THAT TIME. WE WERE CLOSE IN AND HIGH. FINALLY, THE CTLR TOLD US TO JOIN THE FINAL ON THE ASSIGNED HDG (270 DEGS, I THINK) AND MAINTAIN 4000 FT MSL (UNTIL ON FINAL, CLRED VISUAL APCH) DUE TO WBOUND OTTER AT 3500 FT BELOW. I COMPLIED. WE WERE SOMEWHAT HIGH, SO I STARTED IDLE DSCNT AS SOON AS I TURNED FINAL. TCASII IMMEDIATELY GAVE US AN RA TO PULL UP ON CLB. I DID NOT COMPLY WITH THE TCASII RA BECAUSE THE OTTER POS CALLS HAD BEEN N OF US AND THE OTTER HAD RPTED US IN SIGHT AND HAD BEEN TOLD TO MAINTAIN VISUAL SEPARATION. NOTHING WAS SAID ON THE RADIO BY ANYONE. AFTER LNDG, MY FO SAID HE THOUGHT I SHOULD HAVE COMPLIED WITH THE RA. IN HINDSIGHT, HE WAS RIGHT. WHAT IF THE RA HAD BEEN FROM ONE OF THE MANY HELIS OR ANOTHER ACFT IN THE AREA? A GAR WOULD HAVE BEEN BETTER THAN ANY RISK OF COLLISION.

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.