Narrative:

Near miss with B747 runway 25L lax. On final ILS runway 25L, approach controller asked if we had airport in sight. Replied affirmative. Cleared visual runway 25L. Shortly thereafter, approach controller asked if we had a B747 on downwind to base for the north side. Replied affirmative. Told to maintain visual with B747 for the north side. B747 was observed coming off perch from downwind to base. B747 rolled wings level on base. Pointed B747 out to first officer to ensure he saw the same aircraft. First officer stated correctly that B747 should be turning final runway 25L lax just inside of hunda. Approach controller asked if we had airport in sight. Replied affirmative. Cleared visual runway 25L. Approach controller asked if had B747 downwind to base for north side. Replied affirmative. Told to maintain visual with B747. B747 turned base and rolled wings level. Basically constant bearing decreasing range with very slight aftward trend. At that point, it appeared that an overshoot was occurring. First officer started a left turn and started leveling aircraft. TCASII alert 'climb, climb.' started climb at a 220 degree heading. Told approach controller that we had to turn to avoid B747 and could not see him. He had passed behind and below our wing line. Guess B747 offset about 1 mi before he started to turn. We deviated 1 - 1 1/2 mi south of centerline for avoidance. TCASII had B747 300 ft below and very, very close. Symbology for B747 was touching tail of plane symbol on TCASII. Approach controller advised that B747 was turning and we could continue approach. Started slight turn towards field and saw B747 with divergent heading estimated less than 1 mi and 400-500 ft below us. Estimate that he was on centerline for runway 25L or south of centerline. Supplemental information from acn 459794: I was flying a visual approach to runway 25L when approach pointed out a B747 on a base turn to runway 24. When I looked out my window the B747 seemed to be heading directly towards us, so I immediately began a left climbing turn away from the B747. Almost immediately we received a TCASII RA commanding a climb. Shortly thereafter the TCASII commanded a 'monitor vertical climb.' when I began my left climb, I lost visual with the B747. At approximately 1 1/2 mi left of centerline, I began a turn back to the right to obtain visual with the B747. Back on an approximately 250 degree heading, I saw the B747 making a 45 degree intercept back towards runway 24. We landed without any further incident.

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Original NASA ASRS Text

Title: B757 CREW AVOIDED AN NMAC BY FOLLOWING TCASII RA.

Narrative: NEAR MISS WITH B747 RWY 25L LAX. ON FINAL ILS RWY 25L, APCH CTLR ASKED IF WE HAD ARPT IN SIGHT. REPLIED AFFIRMATIVE. CLRED VISUAL RWY 25L. SHORTLY THEREAFTER, APCH CTLR ASKED IF WE HAD A B747 ON DOWNWIND TO BASE FOR THE N SIDE. REPLIED AFFIRMATIVE. TOLD TO MAINTAIN VISUAL WITH B747 FOR THE N SIDE. B747 WAS OBSERVED COMING OFF PERCH FROM DOWNWIND TO BASE. B747 ROLLED WINGS LEVEL ON BASE. POINTED B747 OUT TO FO TO ENSURE HE SAW THE SAME ACFT. FO STATED CORRECTLY THAT B747 SHOULD BE TURNING FINAL RWY 25L LAX JUST INSIDE OF HUNDA. APCH CTLR ASKED IF WE HAD ARPT IN SIGHT. REPLIED AFFIRMATIVE. CLRED VISUAL RWY 25L. APCH CTLR ASKED IF HAD B747 DOWNWIND TO BASE FOR N SIDE. REPLIED AFFIRMATIVE. TOLD TO MAINTAIN VISUAL WITH B747. B747 TURNED BASE AND ROLLED WINGS LEVEL. BASICALLY CONSTANT BEARING DECREASING RANGE WITH VERY SLIGHT AFTWARD TREND. AT THAT POINT, IT APPEARED THAT AN OVERSHOOT WAS OCCURRING. FO STARTED A L TURN AND STARTED LEVELING ACFT. TCASII ALERT 'CLB, CLB.' STARTED CLB AT A 220 DEG HDG. TOLD APCH CTLR THAT WE HAD TO TURN TO AVOID B747 AND COULD NOT SEE HIM. HE HAD PASSED BEHIND AND BELOW OUR WING LINE. GUESS B747 OFFSET ABOUT 1 MI BEFORE HE STARTED TO TURN. WE DEVIATED 1 - 1 1/2 MI S OF CTRLINE FOR AVOIDANCE. TCASII HAD B747 300 FT BELOW AND VERY, VERY CLOSE. SYMBOLOGY FOR B747 WAS TOUCHING TAIL OF PLANE SYMBOL ON TCASII. APCH CTLR ADVISED THAT B747 WAS TURNING AND WE COULD CONTINUE APCH. STARTED SLIGHT TURN TOWARDS FIELD AND SAW B747 WITH DIVERGENT HDG ESTIMATED LESS THAN 1 MI AND 400-500 FT BELOW US. ESTIMATE THAT HE WAS ON CTRLINE FOR RWY 25L OR S OF CTRLINE. SUPPLEMENTAL INFO FROM ACN 459794: I WAS FLYING A VISUAL APCH TO RWY 25L WHEN APCH POINTED OUT A B747 ON A BASE TURN TO RWY 24. WHEN I LOOKED OUT MY WINDOW THE B747 SEEMED TO BE HDG DIRECTLY TOWARDS US, SO I IMMEDIATELY BEGAN A L CLBING TURN AWAY FROM THE B747. ALMOST IMMEDIATELY WE RECEIVED A TCASII RA COMMANDING A CLB. SHORTLY THEREAFTER THE TCASII COMMANDED A 'MONITOR VERT CLB.' WHEN I BEGAN MY L CLB, I LOST VISUAL WITH THE B747. AT APPROX 1 1/2 MI L OF CTRLINE, I BEGAN A TURN BACK TO THE R TO OBTAIN VISUAL WITH THE B747. BACK ON AN APPROX 250 DEG HDG, I SAW THE B747 MAKING A 45 DEG INTERCEPT BACK TOWARDS RWY 24. WE LANDED WITHOUT ANY FURTHER INCIDENT.

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.