Narrative:

In the initial descent phase of flight, issued descent clearance to cross 30 east of agc at 11000' I selected 11000 in the altitude alert counter, took the autoplt off the pms mode (performance management system) and in the control wheel steering mode initiated the descent. During the descent the first officer went off the center frequency and listened to the pittsburgh ATIS. While descending, I reviewed the en route chart for NAVAID frequencys. We descended through 11000, were alerted by the altitude alert system, recovered by 10700' and climbed back up to the assigned 11000'. The center controller made no mention of the altitude deviation. I believe the primary contributing factor was the difference in autoflt systems in the same aircraft. The airline as the result of a merger just intermixed the separate fleets as O january 1990. In the medium large transport I have been flying for 3 yrs, regardless of the autoflt mode of descent (vertical speed, pre departure clearance on level change), the aircraft will only automatically level off at the desired altitude if the autoplt is selected to the pms mode. Also contributing factors include: different locations of the altitude alert counter (glare shield vs console), unusual clearance -- normally issued restriction at 30 mi and 10000', and the fact that both myself and the first officer were being distracted by attention to other details than monitoring the descent.

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Original NASA ASRS Text

Title: ALT BUST.

Narrative: IN THE INITIAL DSCNT PHASE OF FLT, ISSUED DSCNT CLRNC TO CROSS 30 E OF AGC AT 11000' I SELECTED 11000 IN THE ALT ALERT COUNTER, TOOK THE AUTOPLT OFF THE PMS MODE (PERFORMANCE MGMNT SYSTEM) AND IN THE CONTROL WHEEL STEERING MODE INITIATED THE DSCNT. DURING THE DSCNT THE F/O WENT OFF THE CENTER FREQ AND LISTENED TO THE PITTSBURGH ATIS. WHILE DESCENDING, I REVIEWED THE ENRTE CHART FOR NAVAID FREQS. WE DESCENDED THROUGH 11000, WERE ALERTED BY THE ALT ALERT SYSTEM, RECOVERED BY 10700' AND CLIMBED BACK UP TO THE ASSIGNED 11000'. THE CENTER CTLR MADE NO MENTION OF THE ALT DEVIATION. I BELIEVE THE PRIMARY CONTRIBUTING FACTOR WAS THE DIFFERENCE IN AUTOFLT SYSTEMS IN THE SAME ACFT. THE AIRLINE AS THE RESULT OF A MERGER JUST INTERMIXED THE SEPARATE FLEETS AS O JANUARY 1990. IN THE MLG I HAVE BEEN FLYING FOR 3 YRS, REGARDLESS OF THE AUTOFLT MODE OF DSCNT (VERTICAL SPEED, PDC ON LEVEL CHANGE), THE ACFT WILL ONLY AUTOMATICALLY LEVEL OFF AT THE DESIRED ALT IF THE AUTOPLT IS SELECTED TO THE PMS MODE. ALSO CONTRIBUTING FACTORS INCLUDE: DIFFERENT LOCATIONS OF THE ALT ALERT COUNTER (GLARE SHIELD VS CONSOLE), UNUSUAL CLRNC -- NORMALLY ISSUED RESTRICTION AT 30 MI AND 10000', AND THE FACT THAT BOTH MYSELF AND THE F/O WERE BEING DISTRACTED BY ATTN TO OTHER DETAILS THAN MONITORING THE DSCNT.

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.