Narrative:

Assigned altitude was 13000 ft at melon intersection. Descent below altitude to 11500 ft with immediate return to 13000 ft. Captain reported level at 13000 ft and approach instructed us to continue to 8000 ft. Factors: extreme fatigue. The nearly 11-hour flight was preceded by a 5-HR maintenance delay. The crew returned to the hotel for 5 hours after the maintenance delay (and before departure). None of the crew were able to sleep more than about 1 hour. 'Backside of the clock' flying. In the days preceding this trip, the PF flew anc-lax-hnl-lax-hnl-lax-jfk-anc, all at varying times, mostly after midnight. The flight in question was scheduled to depart in the evening but, because of the maintenance delay/duty break, departed around 13 hours later, the next day. During the approximately 32 hours before the end of the flight, the PF had slept approximately 4 hours. Mechanical defect: the altitude select window was inoperative. In fact, this was the cause of the maintenance delay the previous night. This item was deferred by maintenance, as there was no replacement part available. This defective item rendered the altitude alert system inoperative. The crew wrote each assigned altitude on a piece of note paper and placed the note paper forward of the throttles. Confusion as to the assigned altitude, mainly due to fatigue. The assigned altitude was 13000 ft. The STAR includes a note directing aircraft at melon to maintain 250 KTS below 11000 ft. Also, the PF asked the captain what the transition altitude was. The captain replied, '11000 ft.' despite the fact that the correct assigned altitude was written on a piece of paper, these 2 suggestions of '11000 ft,' combined with ATC's instruction to 'maintain high speed' in the descent, extreme fatigue, and an inoperative altitude alerter, led to an unintentional descent to 11000 ft. At approximately 12300 ft, the captain advised the PF of the correct assigned altitude. An immediate recovery was initiated, but 11500 ft was reached prior to establishing a climb. Supplemental information from acn 630170: on descent into hong kong (vhhh), we deviated from an assigned altitude. We were cleared to descend to and maintain FL130. We were on the elato 1B arrival, between point elato and magog. We descended to approximately FL115 before corrective action was taken. We returned to FL130 and no other action was taken. We were below FL130 for approximately 45 seconds. No mention of the altitude excursion was made by ATC. Contributing factors: fatigue. We had been on duty for 17 hours. Distraction. We were distraction with deviating around cumulonimbus in the area on descent. Deferred maintenance item. The altitude alerting system, and the altitude select system of the autoplt were deferred and inoperative.

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Original NASA ASRS Text

Title: A B747-200 FLT CREW RPTED THAT FATIGUE AND LACK OF AN ALT ALERTER CAUSED THEM TO DEVIATE FROM THEIR ASSIGNED ALT BY 1500 FT IN VHHH'S AIRSPACE.

Narrative: ASSIGNED ALT WAS 13000 FT AT MELON INTXN. DSCNT BELOW ALT TO 11500 FT WITH IMMEDIATE RETURN TO 13000 FT. CAPT RPTED LEVEL AT 13000 FT AND APCH INSTRUCTED US TO CONTINUE TO 8000 FT. FACTORS: EXTREME FATIGUE. THE NEARLY 11-HR FLT WAS PRECEDED BY A 5-HR MAINT DELAY. THE CREW RETURNED TO THE HOTEL FOR 5 HRS AFTER THE MAINT DELAY (AND BEFORE DEP). NONE OF THE CREW WERE ABLE TO SLEEP MORE THAN ABOUT 1 HR. 'BACKSIDE OF THE CLOCK' FLYING. IN THE DAYS PRECEDING THIS TRIP, THE PF FLEW ANC-LAX-HNL-LAX-HNL-LAX-JFK-ANC, ALL AT VARYING TIMES, MOSTLY AFTER MIDNIGHT. THE FLT IN QUESTION WAS SCHEDULED TO DEPART IN THE EVENING BUT, BECAUSE OF THE MAINT DELAY/DUTY BREAK, DEPARTED AROUND 13 HRS LATER, THE NEXT DAY. DURING THE APPROX 32 HRS BEFORE THE END OF THE FLT, THE PF HAD SLEPT APPROX 4 HRS. MECHANICAL DEFECT: THE ALT SELECT WINDOW WAS INOP. IN FACT, THIS WAS THE CAUSE OF THE MAINT DELAY THE PREVIOUS NIGHT. THIS ITEM WAS DEFERRED BY MAINT, AS THERE WAS NO REPLACEMENT PART AVAILABLE. THIS DEFECTIVE ITEM RENDERED THE ALT ALERT SYS INOP. THE CREW WROTE EACH ASSIGNED ALT ON A PIECE OF NOTE PAPER AND PLACED THE NOTE PAPER FORWARD OF THE THROTTLES. CONFUSION AS TO THE ASSIGNED ALT, MAINLY DUE TO FATIGUE. THE ASSIGNED ALT WAS 13000 FT. THE STAR INCLUDES A NOTE DIRECTING ACFT AT MELON TO MAINTAIN 250 KTS BELOW 11000 FT. ALSO, THE PF ASKED THE CAPT WHAT THE TRANSITION ALT WAS. THE CAPT REPLIED, '11000 FT.' DESPITE THE FACT THAT THE CORRECT ASSIGNED ALT WAS WRITTEN ON A PIECE OF PAPER, THESE 2 SUGGESTIONS OF '11000 FT,' COMBINED WITH ATC'S INSTRUCTION TO 'MAINTAIN HIGH SPD' IN THE DSCNT, EXTREME FATIGUE, AND AN INOP ALT ALERTER, LED TO AN UNINTENTIONAL DSCNT TO 11000 FT. AT APPROX 12300 FT, THE CAPT ADVISED THE PF OF THE CORRECT ASSIGNED ALT. AN IMMEDIATE RECOVERY WAS INITIATED, BUT 11500 FT WAS REACHED PRIOR TO ESTABLISHING A CLB. SUPPLEMENTAL INFO FROM ACN 630170: ON DSCNT INTO HONG KONG (VHHH), WE DEVIATED FROM AN ASSIGNED ALT. WE WERE CLRED TO DSND TO AND MAINTAIN FL130. WE WERE ON THE ELATO 1B ARR, BTWN POINT ELATO AND MAGOG. WE DSNDED TO APPROX FL115 BEFORE CORRECTIVE ACTION WAS TAKEN. WE RETURNED TO FL130 AND NO OTHER ACTION WAS TAKEN. WE WERE BELOW FL130 FOR APPROX 45 SECONDS. NO MENTION OF THE ALT EXCURSION WAS MADE BY ATC. CONTRIBUTING FACTORS: FATIGUE. WE HAD BEEN ON DUTY FOR 17 HRS. DISTR. WE WERE DISTR WITH DEVIATING AROUND CUMULONIMBUS IN THE AREA ON DSCNT. DEFERRED MAINT ITEM. THE ALT ALERTING SYS, AND THE ALT SELECT SYS OF THE AUTOPLT WERE DEFERRED AND INOP.

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.