FLC OF A B737-300 RESPONDED TO ANOTHER ACFT CALL SIGN DUE TO SIMILAR SOUNDING CALL SIGN AND FLC ACKNOWLEDGMENT BLOCK TO ATC.

Narrative

THE FLT WAS ENRTE FROM SLC TO SJC AND HAD BEEN NAVING VIA THE JAWWS ONE ARR PROC. AFTER PASSING PAPEE INTXN; THE FLT WAS ISSUED A VECTOR HEADING TO INTERCEPT THE ARR NE OF JAWWS INTXN. BAY APCH THEN ISSUED A VECTOR HEADING; TAKING THE FLT OFF OF THE ARR; AND ISSUED CLRNC TO DSND TO 6000 FT. WHILE ON VECTORS AND STILL DSNDING TO 6000 FT BOTH PLTS HEARD AND UNDERSTOOD THAT THE FLT WAS FURTHER CLRED TO DSND TO 4000 FT AND TO CHANGE TO ANOTHER FREQ. THE CAPT RESET THE ALT WINDOW ON THE MCP AND THE FO VERIFIED THE SETTING. THE FO CONFIRMED THE ALT ASSIGNMENT AND FREQ CHANGE. NO REPLY FROM BAY APCH WAS RECEIVED AND THE FO SWITCHED TO THE NEWLY ASSIGNED FREQ AND CONTACTED BAY APCH. THE CTLR ACKNOWLEDGED THE FLT'S CALL AND NO FURTHER COM WAS IMMEDIATELY MADE. THE CTLR DID NOT QUESTION THE ALT ASSIGNMENT FOLLOWING THE FREQ CHANGE. THE FLT CONTINUED A SLOW DSCNT BELOW 6000 FT AND THE CAPT REMARKED THAT THE ASSIGNED ALT WAS BELOW THE MSA DEPICTED ON THE ILS RWY 12R APCH PLATE; BUT ACCEPTED THE ALT AS A MINIMUM VECTOR ALT ISSUED BY BAY APCH. THE FO WAS ABLE TO SEE THE GND AND REMARKED THAT IT APPEARED TO BE COMFORTABLY BELOW THE ACFT. THE FLT WAS OPERATING IN IMC WITH BREAKS IN THE CLOUDS ALLOWING INTERMITTENT VERTICAL VISIBILITY. FLT CONDITIONS INCLUDED RAIN AND CONTINUOUS LIGHT AND OCCASIONAL MODERATE TURB. AS THE SLOW DSCNT (1000 FPM) CONTINUED; BAY APCH ISSUED A VECTOR WHICH CHANGED THE HEADING BY APPROX 20 DEGS TO THE R AND REMARKED THAT THE VECTOR WAS TO AVOID TERRAIN. FURTHER VECTORS WERE ISSUED AND NO XMISSIONS WERE RECEIVED REGARDING THE FLT'S ALT. THE FLT ACQUIRED THE ARPT VISUALLY AND WAS CLRED FOR A VISUAL APCH TO RWY 12R. THE FLT LANDED UNEVENTFULLY AND AS IT WAS TAXIING TO THE GATE; SAN JOSE GND CTL ASKED THE CREW TO CONTACT BAY APCH BY TELEPHONE. THE CAPT CONTACTED BAY APCH BY TELEPHONE AND WAS TOLD THAT THE FLT HAD ACCEPTED A CLRNC FOR ANOTHER FLT ACR Y. THE SUPVR OFFERED THAT HE HAD REVIEWED THE AUDIO TAPE AND HAD HEARD A SOUND CONSISTENT WITH 2 ACFT XMITTING SIMULTANEOUSLY FOLLOWING THE ISSUANCE OF THE CLRNC TO DSND TO 4000 FT AND CHANGE FREQS. HE SAID THAT IT WAS NOT POSSIBLE TO IDENT WHICH ACFT HAD BEEN XMITTING SIMULTANEOUSLY. THE GPWS DID NOT ACTIVATE DURING THE FLT. AT NO TIME WAS THE FLT INFORMED BY RADIO THAT IT HAD ACCEPTED AN INCORRECT CLRNC. NOR WAS ANY XMISSION RECEIVED AMENDING THE ALT CLRNC OR INSTRUCTING THE FLT TO STOP DSCNT OR CLB.