Narrative:

On arrival to sfo from sel, a golden gate 3 arrival was issued with a crossing restr at lestr intersection, 250 KTS, 11000 ft. Just prior to lestr a further clearance of lestr, sfo cross sfo at 11000 ft and descend to 6000 ft, heading 140 degrees. An altitude of 6000 ft was selected on the FMC and the clearance was acknowledged. The aircraft on autoplt failed to level at 11000 ft. At 10700 ft I engaged altitude hold and started a vertical speed climb back to 11000 ft. The descent rate at the time was 100-200 FPM. The flight continued with no further incident. Supplemental information from acn 354877: flight was given a descent to 6000 ft after sfo VOR and a heading for vectors 140 degrees. Moments later planned runway was changed to runway 28L. I proceeded to load new runway and pointed out a shortcut to 'extend centerline' to captain, as he was new on equipment. As new change was executed the captain noticed the aircraft had already started a descent. The descent appeared at first to be uncommanded, but 6000 ft was set in altitude alert window and during the runway change instruction to CDU, it started down before planned execute. Best to have been in flight level change mode. Also backup first officer's did not hear 'after sfo' in descent to 6000 ft. So thought 'all was well' as descent started when captain/first officer were distraction with runway change. Supplemental information from acn 354399: problem arose by setting lower altitude (6000 ft) in altitude alert window prior to aircraft leveling and altitude capture in VNAV mode at 11000 ft. Problem discovered by TCASII alert. FMS/glass cockpits have many subtle features which sometimes can mislead and/or confuse the PF.

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Original NASA ASRS Text

Title: B747-400 FLC EXPERIENCES AN ALTDEV ALT EXCURSION AFTER PROGRAMMING A FUTURE ALT CHANGE IN THEIR FMC.

Narrative: ON ARR TO SFO FROM SEL, A GOLDEN GATE 3 ARR WAS ISSUED WITH A XING RESTR AT LESTR INTXN, 250 KTS, 11000 FT. JUST PRIOR TO LESTR A FURTHER CLRNC OF LESTR, SFO CROSS SFO AT 11000 FT AND DSND TO 6000 FT, HDG 140 DEGS. AN ALT OF 6000 FT WAS SELECTED ON THE FMC AND THE CLRNC WAS ACKNOWLEDGED. THE ACFT ON AUTOPLT FAILED TO LEVEL AT 11000 FT. AT 10700 FT I ENGAGED ALT HOLD AND STARTED A VERT SPD CLB BACK TO 11000 FT. THE DSCNT RATE AT THE TIME WAS 100-200 FPM. THE FLT CONTINUED WITH NO FURTHER INCIDENT. SUPPLEMENTAL INFO FROM ACN 354877: FLT WAS GIVEN A DSCNT TO 6000 FT AFTER SFO VOR AND A HDG FOR VECTORS 140 DEGS. MOMENTS LATER PLANNED RWY WAS CHANGED TO RWY 28L. I PROCEEDED TO LOAD NEW RWY AND POINTED OUT A SHORTCUT TO 'EXTEND CTRLINE' TO CAPT, AS HE WAS NEW ON EQUIP. AS NEW CHANGE WAS EXECUTED THE CAPT NOTICED THE ACFT HAD ALREADY STARTED A DSCNT. THE DSCNT APPEARED AT FIRST TO BE UNCOMMANDED, BUT 6000 FT WAS SET IN ALT ALERT WINDOW AND DURING THE RWY CHANGE INSTRUCTION TO CDU, IT STARTED DOWN BEFORE PLANNED EXECUTE. BEST TO HAVE BEEN IN FLT LEVEL CHANGE MODE. ALSO BACKUP FO'S DID NOT HEAR 'AFTER SFO' IN DSCNT TO 6000 FT. SO THOUGHT 'ALL WAS WELL' AS DSCNT STARTED WHEN CAPT/FO WERE DISTR WITH RWY CHANGE. SUPPLEMENTAL INFO FROM ACN 354399: PROB AROSE BY SETTING LOWER ALT (6000 FT) IN ALT ALERT WINDOW PRIOR TO ACFT LEVELING AND ALT CAPTURE IN VNAV MODE AT 11000 FT. PROB DISCOVERED BY TCASII ALERT. FMS/GLASS COCKPITS HAVE MANY SUBTLE FEATURES WHICH SOMETIMES CAN MISLEAD AND/OR CONFUSE THE PF.

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.