Narrative:

During descent the local altimeter setting given by ATC 1059MB was set in the standby (3RD) altimeter to get the qnh equivalent (in inches of hg) input into ACARS for change over. Simultaneously ATC gave us descent and holding instructions disrupting the mental flow of events, resulting in the failure to reset the standby altimeter to 29.92/1013MB. We were then given numerous altitude clearance changes during a continuous descent to FL80. With the autoplt engaged, the first officer noticed on his altimeter (29.92) that the aircraft did not level off at FL80. By FL78 he analyzed the problem and took corrective action by pressing fl change on the AFDS panel which should have corrected the aircraft back to FL80. It was during the corrective climb that ATC questioned our altitude. After returning to FL80 the crew deduced that the misset standby altimeter resulted in the autoplt not capturing FL80. The standby altimeter was then reset to 29.92/1013MB and a catiii ILS approach was flawlessly accomplished. In conclusion, the problem was caused by a misset standby altimeter with the autoplt engaged. I believe the crew analyzed the problem and took corrective action in an expeditious manner without jeopardizing safety. Supplemental information from acn 199976. Company procedure is to set captain and first officer altimeters to afl (QFE) below 10000 ft, domestic flying with third altimeter to qnh. My habit pattern has been to fly the third altimeter (qnh) below 10000 ft for 24 yrs. On this day approaching lhr the international officer (10) asked me to set (1059MB) the local altimeter setting given in MB into the third altimeter to get qnh (11 mercury) for required input into ACARS. I reset the third altimeter as requested. At the same time we were cleared to descend to 13000 ft. I was working the radio and became involved with the descent procedures, change of radio frequencys, additional descent clrncs, and a hold clearance. I failed to reset the third altimeter to qne (1013MB, 29.92). The first officer flying questioned the aircraft altitude. My first action out of habit was to look at the third altimeter showing us still above 8000 ft descending (because it was misset). Since we were still above trans level the correct altitude was displayed on the captain's and first officer's altitudes (29.92, 1013MB). Do not allow habit patterns of domestic flying interfere with european procedures. Do not become head in the glass cockpit involved with FMC procedures and neglect basic altitude monitoring etc.

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Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT IN DSCNT PROC.

Narrative: DURING DSCNT THE LCL ALTIMETER SETTING GIVEN BY ATC 1059MB WAS SET IN THE STANDBY (3RD) ALTIMETER TO GET THE QNH EQUIVALENT (IN INCHES OF HG) INPUT INTO ACARS FOR CHANGE OVER. SIMULTANEOUSLY ATC GAVE US DSCNT AND HOLDING INSTRUCTIONS DISRUPTING THE MENTAL FLOW OF EVENTS, RESULTING IN THE FAILURE TO RESET THE STANDBY ALTIMETER TO 29.92/1013MB. WE WERE THEN GIVEN NUMEROUS ALT CLRNC CHANGES DURING A CONTINUOUS DSCNT TO FL80. WITH THE AUTOPLT ENGAGED, THE FO NOTICED ON HIS ALTIMETER (29.92) THAT THE ACFT DID NOT LEVEL OFF AT FL80. BY FL78 HE ANALYZED THE PROBLEM AND TOOK CORRECTIVE ACTION BY PRESSING FL CHANGE ON THE AFDS PANEL WHICH SHOULD HAVE CORRECTED THE ACFT BACK TO FL80. IT WAS DURING THE CORRECTIVE CLB THAT ATC QUESTIONED OUR ALT. AFTER RETURNING TO FL80 THE CREW DEDUCED THAT THE MISSET STANDBY ALTIMETER RESULTED IN THE AUTOPLT NOT CAPTURING FL80. THE STANDBY ALTIMETER WAS THEN RESET TO 29.92/1013MB AND A CATIII ILS APCH WAS FLAWLESSLY ACCOMPLISHED. IN CONCLUSION, THE PROBLEM WAS CAUSED BY A MISSET STANDBY ALTIMETER WITH THE AUTOPLT ENGAGED. I BELIEVE THE CREW ANALYZED THE PROBLEM AND TOOK CORRECTIVE ACTION IN AN EXPEDITIOUS MANNER WITHOUT JEOPARDIZING SAFETY. SUPPLEMENTAL INFO FROM ACN 199976. COMPANY PROC IS TO SET CAPT AND FO ALTIMETERS TO AFL (QFE) BELOW 10000 FT, DOMESTIC FLYING WITH THIRD ALTIMETER TO QNH. MY HABIT PATTERN HAS BEEN TO FLY THE THIRD ALTIMETER (QNH) BELOW 10000 FT FOR 24 YRS. ON THIS DAY APCHING LHR THE INTL OFFICER (10) ASKED ME TO SET (1059MB) THE LCL ALTIMETER SETTING GIVEN IN MB INTO THE THIRD ALTIMETER TO GET QNH (11 MERCURY) FOR REQUIRED INPUT INTO ACARS. I RESET THE THIRD ALTIMETER AS REQUESTED. AT THE SAME TIME WE WERE CLRED TO DSND TO 13000 FT. I WAS WORKING THE RADIO AND BECAME INVOLVED WITH THE DSCNT PROCS, CHANGE OF RADIO FREQS, ADDITIONAL DSCNT CLRNCS, AND A HOLD CLRNC. I FAILED TO RESET THE THIRD ALTIMETER TO QNE (1013MB, 29.92). THE FO FLYING QUESTIONED THE ACFT ALT. MY FIRST ACTION OUT OF HABIT WAS TO LOOK AT THE THIRD ALTIMETER SHOWING US STILL ABOVE 8000 FT DSNDING (BECAUSE IT WAS MISSET). SINCE WE WERE STILL ABOVE TRANS LEVEL THE CORRECT ALT WAS DISPLAYED ON THE CAPT'S AND FO'S ALTS (29.92, 1013MB). DO NOT ALLOW HABIT PATTERNS OF DOMESTIC FLYING INTERFERE WITH EUROPEAN PROCS. DO NOT BECOME HEAD IN THE GLASS COCKPIT INVOLVED WITH FMC PROCS AND NEGLECT BASIC ALT MONITORING ETC.

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.