Narrative:

The WX at sfo was several scattered and broken layers. Ceiling was 2000' on previous ATIS. Ceiling was raised on ATIS just prior to approach. Do not remember exact ceiling, but had undercast. We were issued standard 140 degree right from sfo. At approximately 12 DME was issued headings. Final heading was 310 degrees to intercept the 28L localizer. At this time we were between layers. At the time we were given the 310 degree heading we were given traffic at 12 O'clock, commuter type, on a visibility approach to 28R. The commuter aircraft had us in visibility contact and would maintain visibility sep from us. I asked for sep from approach control and was told, 'aircraft on visibility had us in contact and would maintain visibility sep, cleared ILS 28L approach.' we did sight an aircraft in the position that the visibility aircraft should have been at the 11-12 O'clock position (it was the correct aircraft). The copilot was flying the aircraft. I noticed that he had edged the heading to approximately 290 degrees for the intercept because of the discomfort from the proximity of the other plane. At this time we could not see the ground nor the airport and it appeared as though we would have to penetrate a cloud layer on the approach. We stated this to the controller and were again told the other aircraft would maintain visibility sep. We went slightly above G/south so that we would avoid cloud penetration. At this time the aircraft maintaining sep from us was at the 12:30 position. ('How could he keep sep?') I believe that this sequence is extremely dangerous. Particularly at night and with WX. Had we been given a choice prior to the 310 degree heading we would have declined the approach. The safest scenario once issued the clearance was to proceed and take evasive actions as necessary. Visibility perception, particularly at night is marginal at best! This practice should be stopped before we run 2 aircraft together.

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Original NASA ASRS Text

Title: FLT CREW OF ACR MLG QUESTIONS THE USE OF VISUAL SEPARATION FOR NIGHT OPERATION TO PARALLEL RWYS AT SFO.

Narrative: THE WX AT SFO WAS SEVERAL SCATTERED AND BROKEN LAYERS. CEILING WAS 2000' ON PREVIOUS ATIS. CEILING WAS RAISED ON ATIS JUST PRIOR TO APCH. DO NOT REMEMBER EXACT CEILING, BUT HAD UNDERCAST. WE WERE ISSUED STANDARD 140 DEG R FROM SFO. AT APPROX 12 DME WAS ISSUED HDGS. FINAL HDG WAS 310 DEGS TO INTERCEPT THE 28L LOC. AT THIS TIME WE WERE BTWN LAYERS. AT THE TIME WE WERE GIVEN THE 310 DEG HDG WE WERE GIVEN TFC AT 12 O'CLOCK, COMMUTER TYPE, ON A VIS APCH TO 28R. THE COMMUTER ACFT HAD US IN VIS CONTACT AND WOULD MAINTAIN VIS SEP FROM US. I ASKED FOR SEP FROM APCH CTL AND WAS TOLD, 'ACFT ON VIS HAD US IN CONTACT AND WOULD MAINTAIN VIS SEP, CLRED ILS 28L APCH.' WE DID SIGHT AN ACFT IN THE POS THAT THE VIS ACFT SHOULD HAVE BEEN AT THE 11-12 O'CLOCK POS (IT WAS THE CORRECT ACFT). THE COPLT WAS FLYING THE ACFT. I NOTICED THAT HE HAD EDGED THE HDG TO APPROX 290 DEGS FOR THE INTERCEPT BECAUSE OF THE DISCOMFORT FROM THE PROX OF THE OTHER PLANE. AT THIS TIME WE COULD NOT SEE THE GND NOR THE ARPT AND IT APPEARED AS THOUGH WE WOULD HAVE TO PENETRATE A CLOUD LAYER ON THE APCH. WE STATED THIS TO THE CTLR AND WERE AGAIN TOLD THE OTHER ACFT WOULD MAINTAIN VIS SEP. WE WENT SLIGHTLY ABOVE G/S SO THAT WE WOULD AVOID CLOUD PENETRATION. AT THIS TIME THE ACFT MAINTAINING SEP FROM US WAS AT THE 12:30 POS. ('HOW COULD HE KEEP SEP?') I BELIEVE THAT THIS SEQUENCE IS EXTREMELY DANGEROUS. PARTICULARLY AT NIGHT AND WITH WX. HAD WE BEEN GIVEN A CHOICE PRIOR TO THE 310 DEG HDG WE WOULD HAVE DECLINED THE APCH. THE SAFEST SCENARIO ONCE ISSUED THE CLRNC WAS TO PROCEED AND TAKE EVASIVE ACTIONS AS NECESSARY. VIS PERCEPTION, PARTICULARLY AT NIGHT IS MARGINAL AT BEST! THIS PRACTICE SHOULD BE STOPPED BEFORE WE RUN 2 ACFT TOGETHER.

Data retrieved from NASA's ASRS site as of August 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.