Narrative:

On the kepec RNAV one arrival into las as we leveled at 13000 ft, slowing to 250 KTS just prior to clarr, las vegas approach control advised traffic at 1 or 2 O'clock position, 5 mi, VFR target at 12500 ft unconfirmed. We had no visual contact but observed the target on the TCASII display at the correct location and 400 ft below our altitude. I reported that we had no contact, but that our TCASII showed approximately the same unconfirmed altitude for the target. Almost simultaneously we received a TCASII RA of 'climb, climb, climb.' the copilot immediately disconnected the autoplt and initiated a climb, following the TCASII rate of climb command of approximately 2500 FPM to about 13800 ft MSL. The climb command then reduced to about 200 FPM followed by a 'clear of conflict.' we advised approach immediately as we initiated the climb that we were climbing in response to an RA, and we returned to our last assigned altitude as soon as the conflict had been resolved. Upon arrival in las I called approach on the phone and they said that ZLA had later made contact with the VFR traffic, a cessna centurion, and the pilot reported that he had been level at 12500 ft MSL at the time. Supplemental information from acn 601773: just as the autoplt captured the altitude and without any other warning, the TCASII announced, 'climb, climb, climb.' the resolution given on the vsi indicated that a climb of at least 2500 FPM was required, the aircraft symbol was red and 400 ft below us. I disconnected the autoplt and responded as necessary. After climbing about 600 ft, the TCASII gave a different resolution, a green arc of only about 300 FPM climb with red in the entire descent realm. I saw the aircraft fly directly under us as we leveled at about 13800 ft. The other aircraft seemed to be operating legally as were we. The system operated as it was designed and a potential hazard was averted. However, these are exactly the 2 reasons I feel this report is necessary. 500 ft separation between aircraft not talking to the same controller is inadequate. Different altimeter settings, non TCASII equipped aircraft, VFR aircraft climbing, to albeit legal altitudes, through IFR arrival corridors all seem like potentially hazardous ingredients.

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Original NASA ASRS Text

Title: B737-500 CREW AND A C210 HAD NMAC IN LAS CLASS E. THE CREW RESPONDED TO TCASII RA GUIDANCE.

Narrative: ON THE KEPEC RNAV ONE ARR INTO LAS AS WE LEVELED AT 13000 FT, SLOWING TO 250 KTS JUST PRIOR TO CLARR, LAS VEGAS APCH CTL ADVISED TFC AT 1 OR 2 O'CLOCK POS, 5 MI, VFR TARGET AT 12500 FT UNCONFIRMED. WE HAD NO VISUAL CONTACT BUT OBSERVED THE TARGET ON THE TCASII DISPLAY AT THE CORRECT LOCATION AND 400 FT BELOW OUR ALT. I RPTED THAT WE HAD NO CONTACT, BUT THAT OUR TCASII SHOWED APPROX THE SAME UNCONFIRMED ALT FOR THE TARGET. ALMOST SIMULTANEOUSLY WE RECEIVED A TCASII RA OF 'CLB, CLB, CLB.' THE COPLT IMMEDIATELY DISCONNECTED THE AUTOPLT AND INITIATED A CLB, FOLLOWING THE TCASII RATE OF CLB COMMAND OF APPROX 2500 FPM TO ABOUT 13800 FT MSL. THE CLB COMMAND THEN REDUCED TO ABOUT 200 FPM FOLLOWED BY A 'CLR OF CONFLICT.' WE ADVISED APCH IMMEDIATELY AS WE INITIATED THE CLB THAT WE WERE CLBING IN RESPONSE TO AN RA, AND WE RETURNED TO OUR LAST ASSIGNED ALT AS SOON AS THE CONFLICT HAD BEEN RESOLVED. UPON ARR IN LAS I CALLED APCH ON THE PHONE AND THEY SAID THAT ZLA HAD LATER MADE CONTACT WITH THE VFR TFC, A CESSNA CENTURION, AND THE PLT RPTED THAT HE HAD BEEN LEVEL AT 12500 FT MSL AT THE TIME. SUPPLEMENTAL INFO FROM ACN 601773: JUST AS THE AUTOPLT CAPTURED THE ALT AND WITHOUT ANY OTHER WARNING, THE TCASII ANNOUNCED, 'CLB, CLB, CLB.' THE RESOLUTION GIVEN ON THE VSI INDICATED THAT A CLB OF AT LEAST 2500 FPM WAS REQUIRED, THE ACFT SYMBOL WAS RED AND 400 FT BELOW US. I DISCONNECTED THE AUTOPLT AND RESPONDED AS NECESSARY. AFTER CLBING ABOUT 600 FT, THE TCASII GAVE A DIFFERENT RESOLUTION, A GREEN ARC OF ONLY ABOUT 300 FPM CLB WITH RED IN THE ENTIRE DSCNT REALM. I SAW THE ACFT FLY DIRECTLY UNDER US AS WE LEVELED AT ABOUT 13800 FT. THE OTHER ACFT SEEMED TO BE OPERATING LEGALLY AS WERE WE. THE SYS OPERATED AS IT WAS DESIGNED AND A POTENTIAL HAZARD WAS AVERTED. HOWEVER, THESE ARE EXACTLY THE 2 REASONS I FEEL THIS RPT IS NECESSARY. 500 FT SEPARATION BTWN ACFT NOT TALKING TO THE SAME CTLR IS INADEQUATE. DIFFERENT ALTIMETER SETTINGS, NON TCASII EQUIPPED ACFT, VFR ACFT CLBING, TO ALBEIT LEGAL ALTS, THROUGH IFR ARR CORRIDORS ALL SEEM LIKE POTENTIALLY HAZARDOUS INGREDIENTS.

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.