UNABLE TO MAINTAIN VISUAL CONTACT WITH ANOTHER ACFT ON APCH; PLT TRIED TO NOTIFY CTLR; BUT CONGESTED FREQ PREVENTED COM.

Narrative

ON BASE LEG TO FINAL FOR RWY 19L AT SFO; BAY APCH CALLED OUT TFC AT OUR 12-1 O'CLOCK POS. WE ACKNOWLEDGED SEARCHING AS THERE WERE 4 ACFT WITH LIGHTS ILLUMINATED IN THAT AREA. THE RADIO WAS QUITE BUSY. AGAIN APCH ASKED IF WE HAD THE TFC. WE RESPONDED THAT WE DID AND APCH SAID TO KEEP VISUAL SEPARATION WITH THAT TFC AND CLRED US TO INTERCEPT THE RWY 19L LOC. AS WE TURNED TO INTERCEPT THE LOC; IT BECAME APPARENT THAT WE WERE GOING TO TURN INSIDE THE TFC AND LOSE SIGHT OF HIM AS WE COMPLETED THE TURN. I REMEMBER READING ABOUT A PLT RECENTLY VIOLATED AND FINED FOR NOT KEEPING VISUAL CONTACT WITH AN ACFT SO I WAS CONCERNED WHEN WE WERE TURNING INSIDE THE OTHER ACFT. THAT ACFT WAS GOING TO LAND ON RWY 19R. I WANTED TO TELL THE CTLR WE COULDN'T KEEP THAT ACFT IN SIGHT AND DID XMIT THAT FACT; BUT THE CTLR NEVER REALLY ACKNOWLEDGED MY CALL. THERE WERE FEW BREAKS IN RADIO TFC AND THE CTLR CLRED US FOR A VISUAL APCH; CROSS 7 DME AT 3000 FT; AND CONTACT THE TWR. SINCE I WAS STILL TRYING TO KEEP THE OTHER ACFT IN SIGHT; I SELECTED APCH MODE OF THE AUTOFLT CTLS WHICH WOULD MAKE SURE WE DIDN'T OVERSHOOT THE LOC AND WOULD CAPTURE THE GLIDE PATH. I ALLOWED THE AUTOPLT TO FLY DOWN THE GLIDE PATH WHILE STILL TRYING TO TELL THE CTLR ABOUT LOSING SIGHT OF THE OTHER ACFT. AS WE INTERCEPTED THE NORMAL GLIDE PATH WE WERE BELOW 3000 FT AT 7 MI; BUT ON THE NORMAL GLIDE PATH. ON SHORT FINAL; I ASKED TWR TO CALL APCH AND ASK WHAT OUR RESTR WAS. TWR SAID CROSS 10 DME AT 3000 FT. WE WERE JUST ABOUT AT THAT ALT; BUT WE BOTH HEARD 7 DME; THEREFORE THE CONFUSION. CORRECTIVE - TRY TO CALL ON RADIO AND CHK ON RESTR - RADIO WAS BUSY AND WE WERE GETTING CLOSER TO RWY. CONTRIBUTING FACTOR - ON RESERVE; UP AT XA00 AM; CALLED AT XM00 PM FOR ALL NIGHT FLT MSP-SFO-MSP....FATIGUE.