Narrative:

Phl approach control cleared us to descend and maintain 8000 ft, and depart 'bucks' intersection on a heading of 100 degree. Expect ILS runway 27L, phl. The altitude alert selector was correctly set at 8000 ft, and both pilot's altimeters were set at the correct altimeter setting. The altitude alert warning system was functioning correctly and yet I continued descent through 8000 ft, got the altitude alert warning at 300 ft low, but did not arrest the descent until the first officer called 'below 8000 ft.' this occurred at approximately 7600 ft, indicated altitude. Within 10 seconds, I had returned the aircraft to level flight, at 8000 ft, and received no comment from phl approach control regarding an altitude deviation. In a postflt debrief with the crew we determined that the following factors contributed to our missing such a crucial, and routine, flight situation check: 1) we were all tired. We'd checked in for duty at XC00 local pacific time for the first leg of a 5 day pairing. At the time of the incident we had been airborne for 4 hours and were now, flying into the morning sun. 2) the first officer was new to the aircraft, and at the time was preoccupied with tuning and identing ILS frequencys. He was, however, the first of us, to catch the deviation. 3) the flight engineer was busy handling an abnormal situation: an airconditioning 'pack trip,' which had occurred. Simultaneously, with the deviation. 4) for myself: I was sidetracked by the ILS runway change - I expected, and briefed for runway 27R. The change to runway 27L had me scrambling for the appropriate chart.

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Original NASA ASRS Text

Title: A FLC WAS DISTRACTED BY RADIO TUNING, A NEW IAP CLRNC, AND AN EQUIP MALFUNCTION. THE CLRNC ALT WAS OVERSHOT BY 400 FT BEFORE THE CREW RECOGNIZED THE DEV.

Narrative: PHL APCH CTL CLRED US TO DSND AND MAINTAIN 8000 FT, AND DEPART 'BUCKS' INTXN ON A HDG OF 100 DEG. EXPECT ILS RWY 27L, PHL. THE ALT ALERT SELECTOR WAS CORRECTLY SET AT 8000 FT, AND BOTH PLT'S ALTIMETERS WERE SET AT THE CORRECT ALTIMETER SETTING. THE ALT ALERT WARNING SYS WAS FUNCTIONING CORRECTLY AND YET I CONTINUED DSCNT THROUGH 8000 FT, GOT THE ALT ALERT WARNING AT 300 FT LOW, BUT DID NOT ARREST THE DSCNT UNTIL THE FO CALLED 'BELOW 8000 FT.' THIS OCCURRED AT APPROX 7600 FT, INDICATED ALT. WITHIN 10 SECONDS, I HAD RETURNED THE ACFT TO LEVEL FLT, AT 8000 FT, AND RECEIVED NO COMMENT FROM PHL APCH CTL REGARDING AN ALTDEV. IN A POSTFLT DEBRIEF WITH THE CREW WE DETERMINED THAT THE FOLLOWING FACTORS CONTRIBUTED TO OUR MISSING SUCH A CRUCIAL, AND ROUTINE, FLT SIT CHK: 1) WE WERE ALL TIRED. WE'D CHKED IN FOR DUTY AT XC00 LCL PACIFIC TIME FOR THE FIRST LEG OF A 5 DAY PAIRING. AT THE TIME OF THE INCIDENT WE HAD BEEN AIRBORNE FOR 4 HRS AND WERE NOW, FLYING INTO THE MORNING SUN. 2) THE FO WAS NEW TO THE ACFT, AND AT THE TIME WAS PREOCCUPIED WITH TUNING AND IDENTING ILS FREQS. HE WAS, HOWEVER, THE FIRST OF US, TO CATCH THE DEV. 3) THE FE WAS BUSY HANDLING AN ABNORMAL SIT: AN AIRCONDITIONING 'PACK TRIP,' WHICH HAD OCCURRED. SIMULTANEOUSLY, WITH THE DEV. 4) FOR MYSELF: I WAS SIDETRACKED BY THE ILS RWY CHANGE - I EXPECTED, AND BRIEFED FOR RWY 27R. THE CHANGE TO RWY 27L HAD ME SCRAMBLING FOR THE APPROPRIATE CHART.

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.