Narrative:

Near midair -- response to an RA. While being radar vectored to final approach to runway 19R at sna we received an advisory about a VFR aircraft at our 11 O'clock position. We were established on a 270 degree heading passing through about 6000 ft and with a clearance to 4000 ft with the other aircraft level at 4500 ft. We were subsequently cleared to 3000 ft. Socal approach advised that the other aircraft had us in sight but we were unable to see it. Visibility was obscured by haze, I estimate no more than 5-6 mi. First officer was flying and at about 5000 ft, I instructed him to stop the descent as it appeared the aircraft was headed directly for us 600 ft below as displayed on the navigation display. Immediately thereafter, we received an RA which resulted in a climb of about 200 ft to 5200 ft. About 5 seconds before our paths crossed I spotted the aircraft which appeared to be a twin beech pass directly below the nose of the aircraft 700 ft below us. It is my assessment that had we not stopped the descent early, there is a very high probably that we would have collided at 4500 ft. I find it totally unacceptable for any ATC agency to clear an IFR aircraft to fly through the path of another known aircraft in poor visibility without confirmation that both pilots are able to see each other and guarantee separation. Because of the event we were too high to fly the approach and had to request vectors for another approach. It seems to me that the controller was overly anxious to get us down so as not to delay our approach.

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Original NASA ASRS Text

Title: B737 ON DSCNT INTO SNA EXPERIENCES TCASII RA WITH VFR TFC.

Narrative: NEAR MIDAIR -- RESPONSE TO AN RA. WHILE BEING RADAR VECTORED TO FINAL APCH TO RWY 19R AT SNA WE RECEIVED AN ADVISORY ABOUT A VFR ACFT AT OUR 11 O'CLOCK POS. WE WERE ESTABLISHED ON A 270 DEG HDG PASSING THROUGH ABOUT 6000 FT AND WITH A CLRNC TO 4000 FT WITH THE OTHER ACFT LEVEL AT 4500 FT. WE WERE SUBSEQUENTLY CLRED TO 3000 FT. SOCAL APCH ADVISED THAT THE OTHER ACFT HAD US IN SIGHT BUT WE WERE UNABLE TO SEE IT. VISIBILITY WAS OBSCURED BY HAZE, I ESTIMATE NO MORE THAN 5-6 MI. FO WAS FLYING AND AT ABOUT 5000 FT, I INSTRUCTED HIM TO STOP THE DSCNT AS IT APPEARED THE ACFT WAS HEADED DIRECTLY FOR US 600 FT BELOW AS DISPLAYED ON THE NAV DISPLAY. IMMEDIATELY THEREAFTER, WE RECEIVED AN RA WHICH RESULTED IN A CLB OF ABOUT 200 FT TO 5200 FT. ABOUT 5 SECONDS BEFORE OUR PATHS CROSSED I SPOTTED THE ACFT WHICH APPEARED TO BE A TWIN BEECH PASS DIRECTLY BELOW THE NOSE OF THE ACFT 700 FT BELOW US. IT IS MY ASSESSMENT THAT HAD WE NOT STOPPED THE DSCNT EARLY, THERE IS A VERY HIGH PROBABLY THAT WE WOULD HAVE COLLIDED AT 4500 FT. I FIND IT TOTALLY UNACCEPTABLE FOR ANY ATC AGENCY TO CLR AN IFR ACFT TO FLY THROUGH THE PATH OF ANOTHER KNOWN ACFT IN POOR VISIBILITY WITHOUT CONFIRMATION THAT BOTH PLTS ARE ABLE TO SEE EACH OTHER AND GUARANTEE SEPARATION. BECAUSE OF THE EVENT WE WERE TOO HIGH TO FLY THE APCH AND HAD TO REQUEST VECTORS FOR ANOTHER APCH. IT SEEMS TO ME THAT THE CTLR WAS OVERLY ANXIOUS TO GET US DOWN SO AS NOT TO DELAY OUR APCH.

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.