Narrative:

Aircraft #1 departed the lax north runway complex on a 250 degree heading. Aircraft #2 departed the lax south runway complex on a 270 degree heading at the smo 160 degree radial as published on the LAXX2 departure. Aircraft #1 checked on frequency and I issued a climb to 13000 ft and a speed restr of 250 KTS. Aircraft #1 acknowledged the clearance. My next transmission was 'aircraft #2 turn left heading 190 degrees.' the readback I received was 'roger, heading 190 degrees.' no call sign was used. A short time later I observed that both aircraft #2 and aircraft #1 were turning south. I instructed aircraft #1 to stop turn and issued a traffic alert on the B757 1 mi ahead. Aircraft #1 reported traffic in sight. I instructed him to maintain visual separation and verified his departure assignment. I then issued a left turn direct lax VOR to get him further away from the B757. In listening to the tape recording it seems likely that aircraft #1 read back the clearance issued to aircraft #2 without using his call sign. I cannot emphasis strongly enough the importance of including call signs on clearance readbacks. If pilots choose not to use their call signs they are denying air traffic controllers the opportunity to provide a last chance safety check. Call sign usage is up to the pilot. Controllers do not have time on frequency to insist on call sign usage each time pilots choose to omit them.

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Original NASA ASRS Text

Title: 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.

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.