Narrative:

I was in a descent flying the aircraft by use of the autoplt. I received a vector to intercept the localizer. I was having difficulty with the autoplt accepting the localizer intercept mode, so I disengaged the autoplt manually intercepted the localizer, then re-engaged the autoplt and commanded it to track the localizer. I was cleared to maintain 9000 ft, however, when I engaged the autoplt, I failed to rearm altitude capture. I had descended approximately 500 ft below assigned altitude when the first officer alerted me of the deviation. I immediately climbed the aircraft back to 9000 ft. Contributing factors were an approach 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 attention should not be divided. Supplemental information from acn 296141: clearance was maintain 9000 ft until lufco cleared runway 34 ILS. I switched up the ILS and the captain asked me to return to slc, to identify lufco. (Slc ILS doesn't have DME) I switched back to slc and was looking for lufco's DME.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.