Narrative:

Sfo arrival ATIS remarks were indicated that tipp toe and quiet bridge approachs were being made. While on the big sur arrival, the airport was in sight at approximately 20-30 mi out, however there appeared to be a stratus cloud layer over the bay in the runway 28 approach area. As we approached menlo, an air carrier Y flight ahead requested an ILS approach because he did not have the airport in sight. He was cleared for an ILS to 28L. In the vicinity of menlo, bay approach asked us if we had the airport in sight. We did not, and replied 'not in sight.' instructions were then received to intercept the sfo 095 degree right and descend to 1800'. At approximately 7 mi we could only see the approach lights to 28R, so the captain requested and we were cleared for the ILS to 28R. The ILS was flown IMC through the cloud layer, and upon breaking out (bases 1000-1200) an air carrier Z commuter twin engine turbo propeller was observed at our 9-9:30 position, approximately 200' away at the same altitude on a visibility approach to 28L. Subsequent to this event, the captain spoke with a bay approach supervisor. He reviewed the tape and said that his review indicated the approach controller had handled the approachs properly, although they switched to an in trail IFR ILS operation immediately after our approach. The air carrier Z commuter had reported to approach control that they had us and the airport in sight, so they had been cleared for a visibility to 28L. I believe that he would have had great difficulty keeping us in sight as we descended through the stratus cloud layer. This incident reflects concerns re: parallel visibility approachs to runways 28, especially when the WX over the bay in the approach path is significantly different than that at the airport, and pilots cleared on a visibility approach can keep the runway in sight, but not maintain visibility contact with traffic that they have acknowledged in sight. I believe that it is essential that sfo develop a means to observe the actual WX along the final approach path, and alter their approach sequencing accordingly in advance of potential problems.

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Original NASA ASRS Text

Title: ACR FO EXPRESSES CONCERN ABOUT OAK APCH USING CHARTED VISUAL APCHS WHEN THE BAY IS PARTIALLY OBSCURED BY STRATUS CLOUDS.

Narrative: SFO ARR ATIS REMARKS WERE INDICATED THAT TIPP TOE AND QUIET BRIDGE APCHS WERE BEING MADE. WHILE ON THE BIG SUR ARR, THE ARPT WAS IN SIGHT AT APPROX 20-30 MI OUT, HOWEVER THERE APPEARED TO BE A STRATUS CLOUD LAYER OVER THE BAY IN THE RWY 28 APCH AREA. AS WE APCHED MENLO, AN ACR Y FLT AHEAD REQUESTED AN ILS APCH BECAUSE HE DID NOT HAVE THE ARPT IN SIGHT. HE WAS CLRED FOR AN ILS TO 28L. IN THE VICINITY OF MENLO, BAY APCH ASKED US IF WE HAD THE ARPT IN SIGHT. WE DID NOT, AND REPLIED 'NOT IN SIGHT.' INSTRUCTIONS WERE THEN RECEIVED TO INTERCEPT THE SFO 095 DEG R AND DSND TO 1800'. AT APPROX 7 MI WE COULD ONLY SEE THE APCH LIGHTS TO 28R, SO THE CAPT REQUESTED AND WE WERE CLRED FOR THE ILS TO 28R. THE ILS WAS FLOWN IMC THROUGH THE CLOUD LAYER, AND UPON BREAKING OUT (BASES 1000-1200) AN ACR Z COMMUTER TWIN ENG TURBO PROP WAS OBSERVED AT OUR 9-9:30 POS, APPROX 200' AWAY AT THE SAME ALT ON A VIS APCH TO 28L. SUBSEQUENT TO THIS EVENT, THE CAPT SPOKE WITH A BAY APCH SUPVR. HE REVIEWED THE TAPE AND SAID THAT HIS REVIEW INDICATED THE APCH CTLR HAD HANDLED THE APCHS PROPERLY, ALTHOUGH THEY SWITCHED TO AN IN TRAIL IFR ILS OPERATION IMMEDIATELY AFTER OUR APCH. THE ACR Z COMMUTER HAD RPTED TO APCH CTL THAT THEY HAD US AND THE ARPT IN SIGHT, SO THEY HAD BEEN CLRED FOR A VIS TO 28L. I BELIEVE THAT HE WOULD HAVE HAD GREAT DIFFICULTY KEEPING US IN SIGHT AS WE DSNDED THROUGH THE STRATUS CLOUD LAYER. THIS INCIDENT REFLECTS CONCERNS RE: PARALLEL VIS APCHS TO RWYS 28, ESPECIALLY WHEN THE WX OVER THE BAY IN THE APCH PATH IS SIGNIFICANTLY DIFFERENT THAN THAT AT THE ARPT, AND PLTS CLRED ON A VIS APCH CAN KEEP THE RWY IN SIGHT, BUT NOT MAINTAIN VIS CONTACT WITH TFC THAT THEY HAVE ACKNOWLEDGED IN SIGHT. I BELIEVE THAT IT IS ESSENTIAL THAT SFO DEVELOP A MEANS TO OBSERVE THE ACTUAL WX ALONG THE FINAL APCH PATH, AND ALTER THEIR APCH SEQUENCING ACCORDINGLY IN ADVANCE OF POTENTIAL PROBS.

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.