FLC WAS DISTRACTED DURING A HIGH WORKLOAD TIME (DSCNT APCH PHASE); AND DSNDED THROUGH AN ASSIGNED ALT.

Narrative

I WAS IN A DSCNT FLYING THE ACFT BY USE OF THE AUTOPLT. I RECEIVED A VECTOR TO INTERCEPT THE LOC. I WAS HAVING DIFFICULTY WITH THE AUTOPLT ACCEPTING THE LOC INTERCEPT MODE; SO I DISENGAGED THE AUTOPLT MANUALLY INTERCEPTED THE LOC; THEN RE-ENGAGED THE AUTOPLT AND COMMANDED IT TO TRACK THE LOC. I WAS CLRED TO MAINTAIN 9000 FT; HOWEVER; WHEN I ENGAGED THE AUTOPLT; I FAILED TO REARM ALT CAPTURE. I HAD DSNDED APPROX 500 FT BELOW ASSIGNED ALT WHEN THE FO ALERTED ME OF THE DEV. I IMMEDIATELY CLBED THE ACFT BACK TO 9000 FT. CONTRIBUTING FACTORS WERE AN APCH PHASE MOVING AT A RAPID PACE; WHILE FLYING IN WX; AND AN AUTOPLT THAT WOULD NOT ACCEPT CERTAIN COMMANDS. A FACTOR AFFECTING THE QUALITY OF HUMAN PERFORMANCE WOULD BE THE B-727 AUTOPLT. IT IS OLD TECHNOLOGY AND LABOR INTENSIVE AT TIMES THAT ATTN SHOULD NOT BE DIVIDED. SUPPLEMENTAL INFO FROM ACN 296141: CLRNC WAS MAINTAIN 9000 FT UNTIL LUFCO CLRED RWY 34 ILS. I SWITCHED UP THE ILS AND THE CAPT ASKED ME TO RETURN TO SLC; TO IDENT LUFCO. (SLC ILS DOESN'T HAVE DME) I SWITCHED BACK TO SLC AND WAS LOOKING FOR LUFCO'S DME.