B767 FLT CREW DESCENDS BELOW ASSIGNED ALT WHEN CAPT LOSES SITUATIONAL AWARENESS AND ORDERS A DESCENT PREMATURELY DURING APPROACH.

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ON APCH TO ZURICH; 4000 FT ON VECTORS FOR THE ILS 14; WE WERE TOLD TO HOLD 4000 FT TILL ESTABLISHED ON THE LOC. THE CTLR SAID SOMETHING TO US WHICH I DIDN'T UNDERSTAND. THE CAPT TOLD ME TO DSND AND I ASKED AGAIN WHAT THE INSTRUCTIONS HAD BEEN. THE CAPT AGAIN TOLD ME TO DSND. I STARTED A DSCNT TO 3000 FT THEN THE CTLR ASKED OUR ALT AND WHY WE WERE DSNDING. THE CAPT PRESSED ALT HOLD AND WE LEVELED OFF AT 3200 FT. THE CTLR ASKED AGAIN WHY WE WERE DSNDING. THE CAPT HAD THOUGHT WE WERE ABOVE THE GS INSTEAD OF BELOW. SUPPLEMENTAL INFO FROM ACN 797283: I'M THE RELIEF PLT ON A 3-MAN CREW. THE CAPT IS A LINE CHK AIRMAN ADMINISTERING A TRANSOCEANIC OPERATING EXPERIENCE TO A FIRST YR NEW HIRE. AFTER RECEIVING CLRNC TO THE INITIAL APCH ALT; APCH ASKED FOR A WIND READOUT. THIS DISTR THE CAPT AND SITUATIONAL AWARENESS WAS MOMENTARILY LOST CAUSING THE CAPT TO 'FEEL' HE WAS HIGH ON THE GLIDE PATH WHEN ACTUALLY THE ACFT WAS BELOW THE GLIDE PATH. CAPT DIRECTED A DSCNT BELOW THE INITIAL APCH ALT AND SHORTLY THEREAFTER; ZURICH APCH CALLED OUR FLT TWICE THAT WE WERE BELOW THE GLIDE PATH INTERCEPT PUBLISHED ALT. WE DSNDED 400 FT BELOW PUBLISHED INTERCEPT ALT AND THEN LEVELED OFF TO RECAPTURE AND PROCEED WITH THE APCH.