Narrative:

Our aircraft was 10 mi northwest of amigo intersection on the julian arrival to lax airport. Lax controller (125.85) advised us of VFR traffic at our 11 O'clock position 25 mi at 15500 ft. We observed the traffic on our TCASII system and visually sighting his lights and advised ATC of traffic 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 altitude readout -300. We asked ATC what the altitude was of our traffic. ATC advised altitude 15500 ft, an small transport. At the 5 mi range on our TCASII the yellow warning light went to red and a voice activated climb warning given by the TCASII. I quickly looked at, saw that the VFR traffic was reading out on the TCASII at 00 ft and a visual indication to us was that he appeared to be at our altitude. I quickly disconnected the autoplt and made a rapid climb to 17000 ft. As the first officer advised ATC of our departure from 16000 ft to 17000 ft because of our TCASII warning. The VFR traffic passed below us at what appeared to my first officer at or near 16000 ft. It appeared to me that the VFR traffic was beginning to climb to our altitude from the TCASII readout. After the traffic moved towards our 2 O'clock position I immediately returned to 16000 ft and so advised ATC. There was never any conflict with any traffic above us by visual or by the TCASII prior to climbing to and back down to our assigned altitude. On arrival I called and talked with the ATC supervisor for area 'C' and explained why I climbed without a clearance to 17000 ft. He said that the VFR traffic was at 15600 ft and never deviated from that altitude. I said that TCASII issued me the warning and it looked to me that the aircraft had climbed up to my altitude and this is why I took the action to leave my altitude. I then asked if controller had an altitude 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 traffic and he said yes. I asked why he did not vector me out of the way of the VFR traffic. 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 checking it out, no violation at his level would be filed for altitude deviation and/or separation. I thanked him. He further added that the information would be sent back to washington for review. In my opinion I took the correct course of action with the information at hand. I believe the TCASII system was operating properly. I would be surprised if the system had malfunctioned. The TCASII had been working normally all day on this aircraft. I contacted our maintenance supervisor to have the TCASII unit pulled and sent back to our main maintenance base for testing to determine if the unit had malfunctioned or was operating as advertised.

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Original NASA ASRS Text

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

Narrative: 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.

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.