A G4 FO MONITORING THE CAPT'S TEB VOR-DME-A APCH FAILED TO SEE THE CAPT RESET THE MCP ALT SET AND DSND BELOW A XING RESTR.

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WE WERE CLRED FOR THE VOR/DME-A APCH AT TEB. THE PIC; WHO WAS THE PF HAD PROGRAMMED THE FMS BEFOREHAND WITH THE APPLICABLE WAYPOINTS AND XING RESTRS FOR THE APCH INTO THE FMS. I DOUBLE-CHKED HIS PROGRAMMING AND SAW THAT EVERYTHING WAS ENTERED CORRECTLY. HE WAS GOING TO EXECUTE THE APCH IN BLUE (USING THE FMS) AND I WAS GOING TO MONITOR THE APCH IN GREEN (RAW DATA). CLRED FOR THE APCH; WE WERE INSTRUCTED TO CROSS WANES INTXN AT 3000 FT; CLIFO INTXN AT 2000 FT AND CROSS OVER THE ARPT AT 1500 FT; EXACTLY AS PROGRAMMED IN THE FMS -- NO CONFUSION OF WHAT WE HAD TO DO AS FAR AS COURSE; WAYPOINTS; AND ALTS. WE CROSSED WANES AT 3000 FT AND THE PF RESET THE ALT ALERTER TO 2000 FT; THE CLIFO XING ALT. SHORTLY BEFORE CLIFO I NOTICED THAT OUR ALT WAS 2200 FT AND DSNDING ON SCHEDULE. I WAS LOOKING AT THE ARPT AND COMPLETING THE APCH CHKLIST. I LOOKED AT OUR ALT AGAIN AND NOTICED THAT WE WERE DSNDING THROUGH 1800 FT. THIS WAS BEFORE CLIFO. I MENTIONED TO THE PF THAT WE HAD TO STOP DSCNT AT 2000 FT AND CROSS CLIFO AT 2000 FT. THE TWR WAS CALLING US NOW AND I WAS TRYING TO GET THE PF TO STOP DSCNT. THE PF YELLED AT ME TO ANSWER THE TWR. THE TWR HAD NOTICED THAT WE HAD DSNDED BELOW 2000 FT. WE LEVELED AT 1500 FT XING CLIFO AT ABOUT 1500 FT. THE PF THEN RECOGNIZED THAT HE HAD STARTED HIS DSCNT TOO SOON AND SO STATED. THE ALT ALERTER HAD BEEN RESET TO 1500 FT BY THE PF AND HE USED EITHER THE 'VERT SPD' MODE OR THE 'FLT LEVEL CHANGE' MODE TO DSND TO 1500 FT TOO EARLY. THERE WAS NO VOCALIZING BY THE PF OF THE FACT THAT HE WAS RESETTING THE ALT ALERTER TO 1500 FT OR THAT HE WAS DSNDING TO 1500 FT. I IMPROPERLY MONITORED THE APCH IN THAT I DIDN'T SEE THE PF DSND EARLY FROM 2000 FT. WE HAD BRIEFED THE APCH SO WELL; AND WE BOTH HAVE EXECUTED THIS APCH MANY TIMES THAT I FELT; KNEW; THAT THIS APCH WOULD BE EXECUTED PROPERLY. I AM AT A LOSS TO EXPLAIN WHY THE PF DSNDED TO 1500 FT TOO EARLY. A GOOD BRIEFING DOES NOT NECESSARILY LEAD TO A GOOD APCH. VOCALIZATION BTWN THE FLT CREW MEMBERS ABOUT WHAT EACH IS DOING (CHANGING THE ALT ALERTER; STARTING A DSCNT; ETC) IS ABSOLUTELY NECESSARY. PROPER MONITORING IS ALSO NECESSARY. I WAS TAKEN OUT OF THE LOOP WHEN THE PF DECIDED TO DO THE RESETTING OF THE ALT ALERTER DURING THE APCH AND NOT COMMAND ME TO DO IT OR VOCALIZE WHAT HE WAS DOING. I GUESS I ASSUMED THE APCH WOULD GO AS BRIEFED SINCE WE HAD A GOOD APCH BRIEFING; AND BOTH OF US WERE FAMILIAR WITH THE APCH. THE PF IS A GOOD PLT AND MAKES VERY FEW MISTAKES. ONE CANNOT ASSUME. I WAS MONITORING THE APCH BUT MY ATTN WAS DIVERTED BY CHKLISTS AND LOOKING AT THE ARPT. I SAW THE ALT WAS DSNDING THROUGH 1800 FT AND RELAYED THIS TO THE PF. HE CUT ME OFF AND TOLD ME TO ANSWER THE TWR. THE APCH COULD HAVE BEEN SALVAGED AT THIS POINT BY STOPPING THE DSCNT AND CLBING BACK TO 2000 FT; BUT THE PF WAS 'HELL-BENT' ON 1500 FT AND HAD LITTLE INTEREST IN WHAT I HAD TO SAY. I HAVE FLOWN WITH THIS PLT MANY TIMES BEFORE AND HE DOES NOT LISTEN TO HIS COPLTS; ESPECIALLY SUGGESTIONS OR CORRECTIONS. ANY FURTHER ATTEMPT ON MY PART TO TRY; IN THIS CASE; STOP THE DSCNT WOULD HAVE BEEN COUNTER-PRODUCTIVE AND DID BRING A STRONG REBUKE FROM THE PF; 'MY JOB IS TO FLY THE AIRPLANE; YOUR JOB IS TO TALK ON THE RADIO;' NOT EXACTLY HIS WORDS BUT CLOSE. HE'S A RETIRED AIRLINE CAPT AND HE HAS YET TO MAKE HIS FIRST MISTAKE. A LOUSY SIT.