Narrative:

Aircraft X was on vectors on downwind to ILS runway 24R. Aircraft X was approximately 10 mi northeast of lax at 6000 ft when I slowed it to 180 KTS; requiring aircraft X to level off at 6000 ft. Aircraft Y (BE40) was on a heading 280 degrees; vectors to smo visual approach. At 8000 ft; traffic was exchanged between both aircraft. I descended aircraft Y to 7000 ft and advised he would be stepped down reference traffic on downwind; a B777. At 3 mi separation; I reissued traffic instructions to aircraft Y as 'traffic 11:30 O'clock position; 3 mi; 6000 ft; descending B777.' as I unkeyed; I observed aircraft Y below assigned altitude at 6800 ft. Aircraft Y responded that he saw the traffic and was diving under him. I saw aircraft Y at 6600 ft. I instructed aircraft Y to level off. Observing aircraft Y continuing his descent; I continued with 'turn right; turn right.' aircraft Y replied with I am 'diving' under traffic or something like that; but diving was again used. At this point the aircraft were on a collision course approximately 1/2 mi apart with aircraft X at 6000 ft and aircraft Y at 6100 ft. I transmitted to aircraft X 'traffic alert; traffic descending in front of you.' aircraft X responded in a very panicked voice; as mine had been; 'TCAS climb.' targets merged with no observed difference between altitudes. I could not tell who went under who. Targets came apart without a collision and both aircraft proceeded to their destinations. I was relieved of my duties. Aircraft Y called about my poor service. Aircraft X declined to call the facility. A pilot deviation is being filed by the FAA.

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Original NASA ASRS Text

Title: SCT CTLR DESCRIBES NMAC AS LAX AND SMO ARR ACFT CONFLICT AFTER SMO TFC DSNDS WITHOUT CLRNC.

Narrative: ACFT X WAS ON VECTORS ON DOWNWIND TO ILS RWY 24R. ACFT X WAS APPROX 10 MI NE OF LAX AT 6000 FT WHEN I SLOWED IT TO 180 KTS; REQUIRING ACFT X TO LEVEL OFF AT 6000 FT. ACFT Y (BE40) WAS ON A HDG 280 DEGS; VECTORS TO SMO VISUAL APCH. AT 8000 FT; TFC WAS EXCHANGED BTWN BOTH ACFT. I DSNDED ACFT Y TO 7000 FT AND ADVISED HE WOULD BE STEPPED DOWN REF TFC ON DOWNWIND; A B777. AT 3 MI SEPARATION; I REISSUED TFC INSTRUCTIONS TO ACFT Y AS 'TFC 11:30 O'CLOCK POS; 3 MI; 6000 FT; DSNDING B777.' AS I UNKEYED; I OBSERVED ACFT Y BELOW ASSIGNED ALT AT 6800 FT. ACFT Y RESPONDED THAT HE SAW THE TFC AND WAS DIVING UNDER HIM. I SAW ACFT Y AT 6600 FT. I INSTRUCTED ACFT Y TO LEVEL OFF. OBSERVING ACFT Y CONTINUING HIS DSCNT; I CONTINUED WITH 'TURN R; TURN R.' ACFT Y REPLIED WITH I AM 'DIVING' UNDER TFC OR SOMETHING LIKE THAT; BUT DIVING WAS AGAIN USED. AT THIS POINT THE ACFT WERE ON A COLLISION COURSE APPROX 1/2 MI APART WITH ACFT X AT 6000 FT AND ACFT Y AT 6100 FT. I XMITTED TO ACFT X 'TFC ALERT; TFC DSNDING IN FRONT OF YOU.' ACFT X RESPONDED IN A VERY PANICKED VOICE; AS MINE HAD BEEN; 'TCAS CLB.' TARGETS MERGED WITH NO OBSERVED DIFFERENCE BTWN ALTS. I COULD NOT TELL WHO WENT UNDER WHO. TARGETS CAME APART WITHOUT A COLLISION AND BOTH ACFT PROCEEDED TO THEIR DESTS. I WAS RELIEVED OF MY DUTIES. ACFT Y CALLED ABOUT MY POOR SVC. ACFT X DECLINED TO CALL THE FACILITY. A PLTDEV IS BEING FILED BY THE FAA.

Data retrieved from NASA's ASRS site as of January 2009 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.