B767 TOOK TURN CLRNC FOR A B757 RESULTING IN A LTSS. RPTR RECEIVED AN UNIDENTED ACKNOWLEDGMENT OF TURN INSTRUCTION. NO VERIFICATION OF CALLER WAS MADE TO DETERMINE WHICH ACFT RESPONDED TO CLRNC. PLTDEV.

Narrative

ACFT #1 DEPARTED THE LAX NORTH RWY COMPLEX ON A 250 DEG HDG. ACFT #2 DEPARTED THE LAX SOUTH RWY COMPLEX ON A 270 DEG HDG AT THE SMO 160 DEG RADIAL AS PUBLISHED ON THE LAXX2 DEP. ACFT #1 CHKED ON FREQ AND I ISSUED A CLB TO 13000 FT AND A SPD RESTR OF 250 KTS. ACFT #1 ACKNOWLEDGED THE CLRNC. MY NEXT XMISSION WAS 'ACFT #2 TURN L HDG 190 DEGS.' THE READBACK I RECEIVED WAS 'ROGER; HDG 190 DEGS.' NO CALL SIGN WAS USED. A SHORT TIME LATER I OBSERVED THAT BOTH ACFT #2 AND ACFT #1 WERE TURNING S. I INSTRUCTED ACFT #1 TO STOP TURN AND ISSUED A TFC ALERT ON THE B757 1 MI AHEAD. ACFT #1 RPTED TFC IN SIGHT. I INSTRUCTED HIM TO MAINTAIN VISUAL SEPARATION AND VERIFIED HIS DEP ASSIGNMENT. I THEN ISSUED A L TURN DIRECT LAX VOR TO GET HIM FURTHER AWAY FROM THE B757. IN LISTENING TO THE TAPE RECORDING IT SEEMS LIKELY THAT ACFT #1 READ BACK THE CLRNC ISSUED TO ACFT #2 WITHOUT USING HIS CALL SIGN. I CANNOT EMPHASIS STRONGLY ENOUGH THE IMPORTANCE OF INCLUDING CALL SIGNS ON CLRNC READBACKS. IF PLTS CHOOSE NOT TO USE THEIR CALL SIGNS THEY ARE DENYING AIR TFC CTLRS THE OPPORTUNITY TO PROVIDE A LAST CHANCE SAFETY CHK. CALL SIGN USAGE IS UP TO THE PLT. CTLRS DO NOT HAVE TIME ON FREQ TO INSIST ON CALL SIGN USAGE EACH TIME PLTS CHOOSE TO OMIT THEM.