ACR LGT ALTDEV EXCURSION FROM CLRNC ALT IN RESPONSE TO TCASII RA.

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OUR ACFT WAS 10 MI NW OF AMIGO INTXN ON THE JULIAN ARR TO LAX ARPT. LAX CTLR (125.85) ADVISED US OF VFR TFC AT OUR 11 O'CLOCK POS 25 MI AT 15500 FT. WE OBSERVED THE TFC ON OUR TCASII SYS AND VISUALLY SIGHTING HIS LIGHTS AND ADVISED ATC OF TFC IN SIGHT. THE ALTIMETER WAS SET AT 29.96 AS GIVEN BY CENTER. AT THE 10 MI RANGE ON OUR TCASII WE OBSERVED OUR YELLOW WARNING LIGHT COME ON AND ALT READOUT -300. WE ASKED ATC WHAT THE ALT WAS OF OUR TFC. ATC ADVISED ALT 15500 FT; AN SMT. AT THE 5 MI RANGE ON OUR TCASII THE YELLOW WARNING LIGHT WENT TO RED AND A VOICE ACTIVATED CLB WARNING GIVEN BY THE TCASII. I QUICKLY LOOKED AT; SAW THAT THE VFR TFC WAS READING OUT ON THE TCASII AT 00 FT AND A VISUAL INDICATION TO US WAS THAT HE APPEARED TO BE AT OUR ALT. I QUICKLY DISCONNECTED THE AUTOPLT AND MADE A RAPID CLB TO 17000 FT. AS THE FO ADVISED ATC OF OUR DEP FROM 16000 FT TO 17000 FT BECAUSE OF OUR TCASII WARNING. THE VFR TFC PASSED BELOW US AT WHAT APPEARED TO MY FO AT OR NEAR 16000 FT. IT APPEARED TO ME THAT THE VFR TFC WAS BEGINNING TO CLB TO OUR ALT FROM THE TCASII READOUT. AFTER THE TFC MOVED TOWARDS OUR 2 O'CLOCK POS I IMMEDIATELY RETURNED TO 16000 FT AND SO ADVISED ATC. THERE WAS NEVER ANY CONFLICT WITH ANY TFC ABOVE US BY VISUAL OR BY THE TCASII PRIOR TO CLBING TO AND BACK DOWN TO OUR ASSIGNED ALT. ON ARR I CALLED AND TALKED WITH THE ATC SUPVR FOR AREA 'C' AND EXPLAINED WHY I CLBED WITHOUT A CLRNC TO 17000 FT. HE SAID THAT THE VFR TFC WAS AT 15600 FT AND NEVER DEVIATED FROM THAT ALT. I SAID THAT TCASII ISSUED ME THE WARNING AND IT LOOKED TO ME THAT THE ACFT HAD CLBED UP TO MY ALT AND THIS IS WHY I TOOK THE ACTION TO LEAVE MY ALT. I THEN ASKED IF CTLR HAD AN ALT ALERT. HE SAID YES; AT 25 MI AND WHEN WE BOTH HAD EACH OTHER IN SIGHT; HE HAD SUPPRESSED THE ALERT. I ASKED IF THE ATC HAD RADIO CONTACT WITH THE VFR TFC AND HE SAID YES. I ASKED WHY HE DID NOT VECTOR ME OUT OF THE WAY OF THE VFR TFC. HE SAID THAT SINCE WE BOTH SAW EACH OTHER THERE WAS NO NEED TO. I THEN ASKED IF HE WAS GOING TO VIOLATE ME. HE SAID AFTER CHKING IT OUT; NO VIOLATION AT HIS LEVEL WOULD BE FILED FOR ALTDEV AND/OR SEPARATION. I THANKED HIM. HE FURTHER ADDED THAT THE INFO WOULD BE SENT BACK TO WASHINGTON FOR REVIEW. IN MY OPINION I TOOK THE CORRECT COURSE OF ACTION WITH THE INFO AT HAND. I BELIEVE THE TCASII SYS WAS OPERATING PROPERLY. I WOULD BE SURPRISED IF THE SYS HAD MALFUNCTIONED. THE TCASII HAD BEEN WORKING NORMALLY ALL DAY ON THIS ACFT. I CONTACTED OUR MAINT SUPVR TO HAVE THE TCASII UNIT PULLED AND SENT BACK TO OUR MAIN MAINT BASE FOR TESTING TO DETERMINE IF THE UNIT HAD MALFUNCTIONED OR WAS OPERATING AS ADVERTISED.