PROX OF OTHER ACFT ON APCH PROC TO SFO ARPT. FLC CONCERN REGARDING PROX TO OTHER ACFT AND CLRNC INTERP. WAS IT A VISUAL APCH; A PARALLEL APCH OR A RESTR SUBJECT TO VISUAL BEING MAINTAINED ON OTHER ACFT?

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WE WERE CLRED FOR THE VISUAL TO RWY 28L WHEN WE IDENTED THE PRECEDING ACFT APCHING RWY 28R WITH THE STIPULATION THAT WE KEEP OUR SPD AT LEAST 180 KTS TO THE BRIDGE. ON SHORT FINAL; OUR AIRSPD WAS OBVIOUSLY MUCH FASTER THAN THE PRECEDING ACFT AND WE PASSED IT ABOUT 1 MI FROM THRESHOLD AT 300-500 FT OF ALT. THE OTHER CREW MEMBERS WERE SURE THIS WAS A PARALLEL APCH. I KEYED THE MIKE TO ADVISE THAT OUR MINIMUM SPD AS CARRYING US PAST THE ACFT APCHING RWY 28R. THERE WAS NO RESPONSE FROM EITHER THE TWR OR THE OTHER ACFT. IN HINDSIGHT; I SHOULD HAVE TAKEN OVER CTL OF THE ACFT AND EXECUTED A GAR TO PREVENT OUR PASSING THE OTHER ACFT. SUPPLEMENTAL INFO FROM ACN 361657: OUTSIDE BRIDGE; NOTICED WE WERE GAINING ON B737; SO PUT GEAR AND FLAPS 35 DEGS DOWN (FINAL FLAPS) AND SLOWED TO OUR APCH SPD OF 148 KTS. BY THE TIME WE REALIZED WE WERE STILL GAINING AND ABOUT TO PASS THE B737 WE WERE SET WITH FINAL GEAR AND FLAPS FOR THE LNDG AND CLRED TO LAND RWY 28L. OUR ONLY OPTION WOULD HAVE BEEN TO MAKE A GAR AT APPROX 400 FT AGL. RECOMMENDATION: APCH AND TWR ADVISE FASTER AND HEAVIER ACFT ON FINAL (OR ABOUT TO TURN FINAL) OF APCH FINAL SPD OF SLOWER ACFT WHEN ON PARALLEL APCHS AS EARLY AS POSSIBLE. CTLR CAN OBTAIN THIS INFO FROM SLOWER ACFT. HEAVIER AND FASTER ACFT CAN THEN DETERMINE WHETHER THEY CAN STAY BEHIND LIGHTER AND SLOWER ACFT OR WILL NEED TO EXECUTE A GAR AT A MUCH HIGHER AND SAFER ALT.