Narrative:

We were flying a scheduled air carrier flight from sfo to sts in a jetstream 31. In the vicinity of sau VOR oakland center advised us that the visibility wasn't very good and that aircraft ahead of us shot the ILS to visual apches when they acquired the airport. Sts ATIS was reporting sky partially obscured 3 mi visibility and haze. We told the oakland controller we would like the sts ILS 32 and at burdie intersection we were cleared for the approach. Approximately 2 mi south of the OM oakland center terminated radar services and handed us off to sts tower. Tower told us to call the airport in sight, plan to circle east if the airport not in sight at 1000 ft advise, also report crossing the OM inbound. We acknowledged the call and reported that we were crossing the marker now. I was flying the airplane so my primary concentration was inside the cockpit, tracking down the ILS. I would estimate visibility in the haze layer between 1000 ft to 3000 ft at about 2 mi. At approximately 1500 ft MSL on the descent, my first officer said 'jeez! Did you see that guy!' simultaneously my peripheral vision picked up an aircraft at 2 O'clock, rapidly passing through 3 O'clock, slightly below us, opposite direction. My first officer got a much better look at the traffic than I did, he described it as 'a white with blue trim cessna single engine retract, possibly a centurion.' as soon as frequency congestion allowed (sts tower was very busy) we called tower and asked if they were aware of the cessna that appeared to be tracking outbound on the localizer. The tower replied 'negative.' we also saw and reported the airport in sight (we were about 3 mi out by then), and we were told to circle east for landing on runway 14. The rest of the flight was uneventful. I feel the hazard of this type of incident happening again is good due to the WX patterns in the area and the amount of general aviation traffic in the area, especially on the weekends. If sts tower was equipped with a remote radar display and/or we were equipped with TCASII (assuming the cessna was squawking mode C) the hazard could be greatly reduced. Regional (commuter) carriers spend more time in the terminal area than our big brothers equipped with TCASII do. It is mystery to me why we don't have TCASII required now, since the terminal area is where the biggest threat of midairs is. It also concerns me that a GA pilot would track outbound on the localizer on such a marginal day, especially if he was advised of traffic inbound on the ILS (assuming this advisory occurred). Also, if the cessna advised the tower of his departure intentions and tower passed that information on to us, we would be more 'heads up' for see and avoid. Postscript: after talking about this incident in the crew lounge, several other pilots related similar accounts in the sts area.

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Original NASA ASRS Text

Title: NMAC

Narrative: WE WERE FLYING A SCHEDULED ACR FLT FROM SFO TO STS IN A JETSTREAM 31. IN THE VICINITY OF SAU VOR OAKLAND CTR ADVISED US THAT THE VISIBILITY WASN'T VERY GOOD AND THAT ACFT AHEAD OF US SHOT THE ILS TO VISUAL APCHES WHEN THEY ACQUIRED THE ARPT. STS ATIS WAS RPTING SKY PARTIALLY OBSCURED 3 MI VISIBILITY AND HAZE. WE TOLD THE OAKLAND CTLR WE WOULD LIKE THE STS ILS 32 AND AT BURDIE INTERSECTION WE WERE CLRED FOR THE APCH. APPROX 2 MI S OF THE OM OAKLAND CTR TERMINATED RADAR SERVICES AND HANDED US OFF TO STS TWR. TWR TOLD US TO CALL THE ARPT IN SIGHT, PLAN TO CIRCLE E IF THE ARPT NOT IN SIGHT AT 1000 FT ADVISE, ALSO RPT XING THE OM INBOUND. WE ACKNOWLEDGED THE CALL AND RPTED THAT WE WERE XING THE MARKER NOW. I WAS FLYING THE AIRPLANE SO MY PRIMARY CONCENTRATION WAS INSIDE THE COCKPIT, TRACKING DOWN THE ILS. I WOULD ESTIMATE VISIBILITY IN THE HAZE LAYER BTWN 1000 FT TO 3000 FT AT ABOUT 2 MI. AT APPROX 1500 FT MSL ON THE DSCNT, MY FO SAID 'JEEZ! DID YOU SEE THAT GUY!' SIMULTANEOUSLY MY PERIPHERAL VISION PICKED UP AN ACFT AT 2 O'CLOCK, RAPIDLY PASSING THROUGH 3 O'CLOCK, SLIGHTLY BELOW US, OPPOSITE DIRECTION. MY FO GOT A MUCH BETTER LOOK AT THE TFC THAN I DID, HE DESCRIBED IT AS 'A WHITE WITH BLUE TRIM CESSNA SINGLE ENG RETRACT, POSSIBLY A CENTURION.' AS SOON AS FREQ CONGESTION ALLOWED (STS TWR WAS VERY BUSY) WE CALLED TWR AND ASKED IF THEY WERE AWARE OF THE CESSNA THAT APPEARED TO BE TRACKING OUTBOUND ON THE LOC. THE TWR REPLIED 'NEGATIVE.' WE ALSO SAW AND RPTED THE ARPT IN SIGHT (WE WERE ABOUT 3 MI OUT BY THEN), AND WE WERE TOLD TO CIRCLE E FOR LNDG ON RWY 14. THE REST OF THE FLT WAS UNEVENTFUL. I FEEL THE HAZARD OF THIS TYPE OF INCIDENT HAPPENING AGAIN IS GOOD DUE TO THE WX PATTERNS IN THE AREA AND THE AMOUNT OF GENERAL AVIATION TFC IN THE AREA, ESPECIALLY ON THE WEEKENDS. IF STS TWR WAS EQUIPPED WITH A REMOTE RADAR DISPLAY AND/OR WE WERE EQUIPPED WITH TCASII (ASSUMING THE CESSNA WAS SQUAWKING MODE C) THE HAZARD COULD BE GREATLY REDUCED. REGIONAL (COMMUTER) CARRIERS SPEND MORE TIME IN THE TERMINAL AREA THAN OUR BIG BROTHERS EQUIPPED WITH TCASII DO. IT IS MYSTERY TO ME WHY WE DON'T HAVE TCASII REQUIRED NOW, SINCE THE TERMINAL AREA IS WHERE THE BIGGEST THREAT OF MIDAIRS IS. IT ALSO CONCERNS ME THAT A GA PLT WOULD TRACK OUTBOUND ON THE LOC ON SUCH A MARGINAL DAY, ESPECIALLY IF HE WAS ADVISED OF TFC INBOUND ON THE ILS (ASSUMING THIS ADVISORY OCCURRED). ALSO, IF THE CESSNA ADVISED THE TWR OF HIS DEP INTENTIONS AND TWR PASSED THAT INFO ON TO US, WE WOULD BE MORE 'HEADS UP' FOR SEE AND AVOID. POSTSCRIPT: AFTER TALKING ABOUT THIS INCIDENT IN THE CREW LOUNGE, SEVERAL OTHER PLTS RELATED SIMILAR ACCOUNTS IN THE STS AREA.

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.