MLG DISTR BY TCASII ALERT LANDS WITHOUT CLRNC.

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FLT MGR-SFO. FLT WAS UNEVENTFUL UNTIL SFO TFC AREA. FLT WAS CLRED FOR A VISUAL APCH ON RWY 28R SFO AND INSTRUCTED TO CONTACT TWR OVER THE SAN MATEO BRIDGE. COPLT WAS FLYING THE APCH; AUTOPLT WAS OFF; THE ILS WAS TUNED FOR RWY 28R AND THE FLT DIRECTOR WAS IN APCH MODE AS BACKUP. WE WERE TOLD TO MAINTAIN AT LEAST 180 KIAS UNTIL BRIDGE. AS THE CAPT SET IN TWR FREQ OVER BRIDGE; WE HAD A TCASII WARNING WITH A PULL UP INDICATION. I STARTED TO DEVIATE AND CLB AS INSTRUCTED THEN THE CAPT IDENTED THE TFC WHICH WAS A TWIN TURBO PROP PASSING US ON THE L FOR RWY 28L. I CONTINUED WITH THIS APCH AND LANDED. AFTER WE TAXIED OFF THE ACTIVE RWY; I NOTICED THAT WE WERE STILL ON APCH'S FREQ. I RADIOED THE TWR AND ASKED IF WE WERE CLRED TO CROSS RWY 28L. TWR REPLIED 'YES; AND WE WERE TRYING TO REACH YOU.' I REPLIED 'ROGER; WE'RE CLR TO CROSS THE L; SORRY; WE WERE TEMPORARILY OFF OF YOUR FREQ.' TAXI IN WAS NORMAL. DUE TO TASK SATURATION IN THE HIGH TFC ENVIRONMENT WE ALLOWED OURSELVES TO LAND WITHOUT CLRNC. ALL SOP'S AND CHKLISTS WERE COMPLIED WITH; INCLUDING THE 1000 FT CALL WHEN I REPLIED 'RWY IN SIGHT 28R; WE'RE CLR TO LAND.' THE CAPT REPEATED 'WE'RE CLR TO LAND.'