A DSNDING B737 OVERSHOT ITS ASSIGNED ALT WHEN THE PIC DOES NOT RESET HIS ALTIMETER TO LCL QNH. CREW HAD NOT COMPLETED THEIR DSCNT CHKLIST ON ACCOUNT OF ATC BURDENS.

Narrative

THE 4TH AMENDMENT TO OUR ARR CLRNC INTO BOSTON WAS A CLRNC TO THE LFV VOR AND THEN EXPECT RADAR VECTORS. WE WERE ON A DSCNT TO 15000 FT AS WE APCHED THE VOR AND STILL HAD NOT RECEIVED A VECTOR FOR AFTER THE VOR. AS WE CROSSED THE LFV VOR WE REQUESTED A HEADING AND APCH CTL CLRED US TO THE SCUPP INTXN. AS WE INTERCEPTED THE OUTBOUND RADIAL TO SCUPP; WE WERE GIVEN A DSCNT CLRNC TO 12000 FT AND HOLDING INSTRUCTIONS AT SCUPP. WE WERE ALSO NOTIFIED OF A RWY CHANGE AND TO NOW EXPECT RWY 22L INSTEAD OF RWY 27. AS WE APCHED SCUPP INTXN THE ACFT LEVELED OFF AT 12000 FT (AUTOPLT ON). THE FO NOTICED THE CAPT HAD NOT RESET HIS ALTIMETER TO THE LCL ALTIMETER SETTING. THE ACFT HAD LEVELED OFF APPROX 200 FT LOW AT 11800 FT. THE ACFT WAS IMMEDIATELY CLBED BACK TO 12000 FT. APCH CTL MADE NO COMMENT ABOUT THE DISCREPANCY AND THE FLT CONTINUED AS PLANNED. I BELIEVE THE PROB WAS CAUSED BY A COMBINATION OF FACTORS. THE CLRNC CHANGES; RWY CHANGE; HOLDING INSTRUCTIONS; AND ALSO A NEW ATIS INFO ALL COMBINED FOR A VERY BUSY COCKPIT ENVIRONMENT. IN THIS PROCESS A DSCNT CHKLIST WAS NOT COMPLETED AND LED TO THE FAULTY ALTIMETER SETTING.