Narrative:

The WX was not a factor, although the afternoon sky was hazy. (ATIS: 30000 thin scattered, 20 mi visibility, temperature 66 degrees, wind 250 degrees at 15 KTS, runways 24 and 25 in use.) the aircraft was an large transport on a scheduled air carrier operation. The captain was flying. We were downwind north of lax, flying eastbound at 5000'. La approach control cleared us for a 'harbor visual approach to runway 25,' and requested that we report turning base leg. Approximately 10 mi northeast of lax we reported 'turning base.' approach requested if we had medium large transport X in sight at '1-2 O'clock.' the captain replied, 'affirmative,' which I relayed to approach. Approach told us to maintain a visual on the traffic, to pass above and behind it, and that we were cleared for a visual approach to runway 25, and to switch to la tower at the OM. We maintained a visual watch on the reported traffic and continued our approach. We began turning onto final approach when approach control inquired in a very concerned tone of voice if we 'still had our traffic?' we replied 'affirmative,' and asked if there was a problem. Approach control said 'yes,' our traffic was now at our 9 O'clock at 2 mi! We looked to our left and immediately saw medium large transport Y, same type, on final approach. We made an immediate left turn and s-turned around medium large transport Y and re-established ourselves on final approach behind the medium large transport Y. We thanked approach for their timely warning. No violation was charged, and the aircraft did not pass close enough to warrant a near miss report. I believe the controller issued our traffic at '1-2 O'clock' on the basis of where the traffic would have been if we had still been flying eastbound downwind. But, because we had already turned southbound on base leg, the '1-2 O'clock traffic' was now at our 9 O'clock. By coincidence, there was another medium large transport at our 'new' 1-2 O'clock position, which would have been at our 5 O'clock if we had still been flying eastbound. The way to prevent this problem in the future is for traffic to be called out according to magnetic bearings, instead of reference to clock positions (which is actually relative bearing). Magnetic bearings remain the same, no matter what the heading of the observing aircraft. I believe that this is a much more precise way of calling traffic, especially when the observing aircraft is in the process of changing headings, such as in the airport traffic pattern.

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Original NASA ASRS Text

Title: ACT LGT STARTED TO TURN IN FRONT OF MLG THEY HAD BEEN CLEARED TO FOLLOW. THERE WERE 2 MLGS ON APCH TO THE ARPT AND THE FLT CREW STARTED TO FOLLOW THE WRONG ACFT.

Narrative: THE WX WAS NOT A FACTOR, ALTHOUGH THE AFTERNOON SKY WAS HAZY. (ATIS: 30000 THIN SCATTERED, 20 MI VIS, TEMP 66 DEGS, WIND 250 DEGS AT 15 KTS, RWYS 24 AND 25 IN USE.) THE ACFT WAS AN LGT ON A SCHEDULED ACR OPERATION. THE CAPT WAS FLYING. WE WERE DOWNWIND N OF LAX, FLYING EBND AT 5000'. LA APCH CTL CLRED US FOR A 'HARBOR VISUAL APCH TO RWY 25,' AND REQUESTED THAT WE RPT TURNING BASE LEG. APPROX 10 MI NE OF LAX WE RPTED 'TURNING BASE.' APCH REQUESTED IF WE HAD MLG X IN SIGHT AT '1-2 O'CLOCK.' THE CAPT REPLIED, 'AFFIRMATIVE,' WHICH I RELAYED TO APCH. APCH TOLD US TO MAINTAIN A VISUAL ON THE TFC, TO PASS ABOVE AND BEHIND IT, AND THAT WE WERE CLRED FOR A VISUAL APCH TO RWY 25, AND TO SWITCH TO LA TWR AT THE OM. WE MAINTAINED A VISUAL WATCH ON THE REPORTED TFC AND CONTINUED OUR APCH. WE BEGAN TURNING ONTO FINAL APCH WHEN APCH CTL INQUIRED IN A VERY CONCERNED TONE OF VOICE IF WE 'STILL HAD OUR TFC?' WE REPLIED 'AFFIRMATIVE,' AND ASKED IF THERE WAS A PROB. APCH CTL SAID 'YES,' OUR TFC WAS NOW AT OUR 9 O'CLOCK AT 2 MI! WE LOOKED TO OUR LEFT AND IMMEDIATELY SAW MLG Y, SAME TYPE, ON FINAL APCH. WE MADE AN IMMEDIATE LEFT TURN AND S-TURNED AROUND MLG Y AND RE-ESTABLISHED OURSELVES ON FINAL APCH BEHIND THE MLG Y. WE THANKED APCH FOR THEIR TIMELY WARNING. NO VIOLATION WAS CHARGED, AND THE ACFT DID NOT PASS CLOSE ENOUGH TO WARRANT A NEAR MISS RPT. I BELIEVE THE CTLR ISSUED OUR TFC AT '1-2 O'CLOCK' ON THE BASIS OF WHERE THE TFC WOULD HAVE BEEN IF WE HAD STILL BEEN FLYING EBND DOWNWIND. BUT, BECAUSE WE HAD ALREADY TURNED SBND ON BASE LEG, THE '1-2 O'CLOCK TFC' WAS NOW AT OUR 9 O'CLOCK. BY COINCIDENCE, THERE WAS ANOTHER MLG AT OUR 'NEW' 1-2 O'CLOCK POS, WHICH WOULD HAVE BEEN AT OUR 5 O'CLOCK IF WE HAD STILL BEEN FLYING EBND. THE WAY TO PREVENT THIS PROB IN THE FUTURE IS FOR TFC TO BE CALLED OUT ACCORDING TO MAGNETIC BEARINGS, INSTEAD OF REF TO CLOCK POSITIONS (WHICH IS ACTUALLY RELATIVE BEARING). MAGNETIC BEARINGS REMAIN THE SAME, NO MATTER WHAT THE HDG OF THE OBSERVING ACFT. I BELIEVE THAT THIS IS A MUCH MORE PRECISE WAY OF CALLING TFC, ESPECIALLY WHEN THE OBSERVING ACFT IS IN THE PROCESS OF CHANGING HDGS, SUCH AS IN THE ARPT TFC PATTERN.

Data retrieved from NASA's ASRS site as of August 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.