B747 LNDG SFO MAY HAVE EXITED CLASS B DURING VISUAL APCH.

Narrative

WE HAD FLOWN UNEVENTFULLY FROM JAPAN TO SFO AND WERE BEING VECTORED FOR AN ILS RWY 28R. WE ACQUIRED THE FIELD VISUALLY WHILE DSNDING TO 3000 FT ON A BASE LEG. WE WERE CLRED FOR THE VISUAL APCH TO RWY 28R. WE HAD BRIEFED THE ILS RWY 28R AND REVIEWED THE QUIET BRIDGE VISUAL RWY 28R. (WE HAD ALSO FLOWN THE QUIET BRIDGE TO RWY 28R 3 DAYS EARLIER.) AS WE CONTINUED TURNING FINAL; I RECOMMENDED TO MY FO THAT HE 'SHOOT FOR 1900 FT;' AS RECOMMENDED FOR A XING ALT AT THE SAN MATEO BRIDGE. AS I RECALL; I CHKED IN WITH SFO TWR RPTING 15 DME ON THE VISUAL TO RWY 28R. I DO NOT RECALL OUR EXACT ALT; BUT RECALL THAT WE WERE CLOSE TO OR AT 1900 FT. WE LANDED ON RWY 28R WITH NO WARNINGS OR ADVISORIES FROM THE TWR AND TAXIED TO OUR GATE. AFTER SOME REST AT THE HOTEL; I REVIEWED THE SFO 10-1 PAGE AND CAME TO THE CONCLUSION THAT; DURING THE APCH; I VERY POSSIBLY EXITED THE FLOOR OF THE CLASS B AIRSPACE. MY COMPANY OP SPECS (FMS) STATE THAT; DURING A VISUAL APCH TO AN AIRFIELD IN CLASS B AIRSPACE; WE MUST REMAIN IN THE CLASS B AIRSPACE DURING THE ENTIRE APCH. HAD WE MAINTAINED OUR LAST ASSIGNED ALT OF 3000 FT UNTIL INTERCEPTING THE GS; THIS RPT WOULD NOT HAVE BEEN SUBMITTED. THIS WAS DAY 6 OF FLYING FOR ME IN THE PREVIOUS 10 DAYS; BUT I DO NOT BELIEVE FATIGUE WAS A FACTOR. WE WERE ALL VERY ALERT AND ALL OPTIONS (ILS/VISUAL) FOR THE APCH HAD BEEN REVIEWED. WHILE THE RESPONSIBILITY IS ULTIMATELY MINE; AN ALT HEADS-UP ABOUT MY ALT FROM THE TWR COULD BE BENEFICIAL IN INSURING MY COMPLIANCE WITH THE AIRSPACE REQUIREMENT; OR A STATEMENT SUCH AS 'REMAIN IN THE CLASS B AIRSPACE; CLRED THE VISUAL APCH' MIGHT ALSO BE HELPFUL IN A SIMILAR SIT.