FLC OF MLG OVERSHOT DSCNT CLRNC ALT ON APCH TO SJC.

Narrative

OUR ARR INTO SJC WAS THE EL NIDO 3. CLRNC READ: CROSS EL NIDO AT 240 OR BELOW TO MAINTAIN 160. AFTER XING EL NIDO FURTHER CLRNC WAS GIVEN TO DSND AND MAINTAIN 120. AFTER THAT FURTHER CLRNC TO MAINTAIN 100. AT 100 WE WERE GIVEN A RADAR VECTOR TO INTERCEPT THE SJC 30L LOC. WE UNDERSTOOD THE CLRNC AND SET 100 INTO THE ALT ALERTER. THE ALT ALERTER IN THIS PARTICULAR ACFT IS LOCATED ON THE FO'S FORWARD PANEL AND IT HAS A HIGH PITCH WHISTLE WARNING SOUND DIFFERENT FROM THE ALL-FAMILIAR 'BONG' I AM USED TO. I BECAME SUSPICIOUS WHEN THE CTLR SAID MAINTAIN 280 KTS. AT THAT TIME I LOOKED DOWN AND REALIZED WE WERE OUT OF 100. IT WAS REALIZED AT 9400 MSL. I IMMEDIATELY CLBED BACK TO 100. JUST BEFORE REACHING 100 I WAS GIVEN CLRNC TO 080. WE DID EXPERIENCE A COM PROBLEM WITH APCH AND DID ASK FOR A DIFFERENT XMITTER. COMS WERE FULLY RESTORED AND FLT CONTINUED NORMALLY. IN MY 25 YRS OF FLYING I'VE NEVER VIOLATED AN ALT RESTRICTION. I REALLY DON'T KNOW WHAT CREATED THE PROBLEM ONLY THAT AFTER YRS OF BECOMING USED TO AN INST'S FAMILIAR LOCATION AND SOUND I FAILED TO HEAR THE UNFAMILIAR SOUND OF THIS PARTICULAR ALT ALERTER. ATC WAS VERY PROFESSIONAL THROUGHOUT THE ENTIRE FLT.