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.

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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.