Narrative:

Copilot was PF on loupe 9 departure SID to cross sjc VOR at 12000 ft with altitude clearance to FL230. Copilot was using autoplt and managed climb on FMS mode with the pre-programmed restr of 12000 ft at sjc VOR. The aircraft however continued to climb higher than 12000 ft just prior to sjc VOR and copilot stopped climb by turning off autoplt and hand-flying the aircraft back to 12000 ft. Maximum altitude reached on captain altimeter was 12400 ft. Same on first officer altimeter. ATC controller noticed the altitude deviation and cleared us to 14000 ft. We initiated climb to 14000 ft but had already returned to 12000 ft when climb was initiated. Captain (myself) was distracted slightly from monitoring instruments by climb checklist and frequency change. On analysis and discussion with copilot as to why aircraft autoplt did not leveloff at 12000 ft we concluded that when copilot set in an altitude change on fmp from 12000 ft to FL230 he inadvertently selected open climb by pulling the altitude change button instead of just selecting the new altitude in the window. This would have deactivated the altitude constraint. Unfortunately neither pilot caught the mistake due to the many tasks that we were accomplishing in a short time frame.

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Original NASA ASRS Text

Title: FO OF AN AIRBUS A320, OVERSHOT THE SID DEP XING ALT DUE TO SETTING THE FMC MODE SELECTOR IN ERROR.

Narrative: COPLT WAS PF ON LOUPE 9 DEP SID TO CROSS SJC VOR AT 12000 FT WITH ALT CLRNC TO FL230. COPLT WAS USING AUTOPLT AND MANAGED CLB ON FMS MODE WITH THE PRE-PROGRAMMED RESTR OF 12000 FT AT SJC VOR. THE ACFT HOWEVER CONTINUED TO CLB HIGHER THAN 12000 FT JUST PRIOR TO SJC VOR AND COPLT STOPPED CLB BY TURNING OFF AUTOPLT AND HAND-FLYING THE ACFT BACK TO 12000 FT. MAX ALT REACHED ON CAPT ALTIMETER WAS 12400 FT. SAME ON FO ALTIMETER. ATC CTLR NOTICED THE ALTDEV AND CLRED US TO 14000 FT. WE INITIATED CLB TO 14000 FT BUT HAD ALREADY RETURNED TO 12000 FT WHEN CLB WAS INITIATED. CAPT (MYSELF) WAS DISTRACTED SLIGHTLY FROM MONITORING INSTS BY CLB CHKLIST AND FREQ CHANGE. ON ANALYSIS AND DISCUSSION WITH COPLT AS TO WHY ACFT AUTOPLT DID NOT LEVELOFF AT 12000 FT WE CONCLUDED THAT WHEN COPLT SET IN AN ALT CHANGE ON FMP FROM 12000 FT TO FL230 HE INADVERTENTLY SELECTED OPEN CLB BY PULLING THE ALT CHANGE BUTTON INSTEAD OF JUST SELECTING THE NEW ALT IN THE WINDOW. THIS WOULD HAVE DEACTIVATED THE ALT CONSTRAINT. UNFORTUNATELY NEITHER PLT CAUGHT THE MISTAKE DUE TO THE MANY TASKS THAT WE WERE ACCOMPLISHING IN A SHORT TIME FRAME.

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.