A B757 FLT CREW WAS DISTRACTED LOOKING FOR TFC WHICH LED THEM TO INADVERTENTLY LAND WITHOUT A CLRNC FROM TWR.

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DURING FMS BRIDGE VISUAL APCH ATC COMMANDED 210 KT APCH; WERE TOLD TO LOOK FOR A KING AIR ON FINAL FOR RWY 28L. COULD NOT SEE HIM IN THE CLUTTER OF THE HILL. APCHING THE BRIDGE A LIGHT TWIN WENT UNDERNEATH US CAUSING US TO QUESTION JUST WHAT THE OTHER ACFT WAS DOING. ATC CONFIRMED ONE BENEATH US; AND THEN ASKED US DID WE HAVE THE KING AIR FOR RWY 28L. WE REPLIED NEGATIVE. XING THE BRIDGE AND TURNING TO FINAL THE CAPT; PF; SLOWED AND CONFIGURED THE ACFT WHILE I WAS FINISHING THE CHKLIST. INTERCEPTING FINAL ATC TOLD US WE WOULD HAVE TO GO AROUND IF WE DID NOT HAVE A VISUAL ON THE KING AIR. WE FINALLY ACQUIRED HIM AS HE HAD THE BAY BENEATH HIM TO PROVIDE CONTRAST. AT THAT TIME; WE BOTH HEARD 'CLRED TO LAND;' SLID THE LAST ITEM ON THE MECHANICAL CHKLIST; AND DEDICATED OUR ATTN TO THE LNDG AND LNDG CALLOUTS. ON ROLLOUT; WE REALIZED WE WERE NOT ON TWR FREQ. WE WERE DISTRACTED BY THE REQUIREMENT TO ACQUIRE A SMALL TARGET IN A BUSY BACKGROUND; COUPLED WITH A HIGHER THAN USUAL APCH SPD; DUE TO LOOKING FOR THE TFC; SLIGHTLY BEHIND AT THE BRIDGE. THE CALL THAT WE WOULD GO AROUND IF TFC WAS NOT IN SIGHT RIVETED EACH OF OUR ATTN TO FIND THE TFC. BEING SO CLOSE TO LNDG; WE BELIEVED WE HEARD A CLRNC TO LAND. THIS APCH SETS UP AIRCREWS TO GET OUT OF ANY SEMBLANCE OF USUAL RHYTHM AND HABIT PATTERNS. THE LARGER ACFT ON RWY 28L ARE EASIER TO SEE; BUT PRESENT A WORRISOME APPEARANCE WHEN IN A WING UP ATTITUDE AND JOINING COURSE; LEAVING THOSE ON RWY 28R WONDERING IF THIS IS THE ONE WHO WILL OVERSHOOT AND CAUSE A CONFLICT. THE SMALLER ACFT ARE MORE DIFFICULT TO SEE; AND PRESENT THE DIFFICULTY OF KNOWING YOU HAVE ADEQUATE CLRNC WHEN JOINING FINAL. HAVING SAID THAT; I WILL RECHK IN THE FUTURE THAT I HAVE TALKED TO TWR AND RECEIVED PROPER CLRNC.