Narrative:

We were leveling off from climb at FL310. The autoplt was engaged and the aircraft leveled off at FL310 and then started to climb with the autoplt on altitude hold. We spotted the climb at about FL310 and rolled the autoplt pitch (vertical speed) control to descend. I was about to disengage the autoplt when it finally responded to inputs and leveled off and started back down to FL310 maximum. Altitude was FL313. The autoplt did the same thing again when I leveled off at FL310, but this time I disengaged the autoplt and trimmed aircraft by hand. Autoplt worked normally after re- engagement.

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Original NASA ASRS Text

Title: MLG CLBED ABOVE ASSIGNED CRUISE ALT WHEN THE AUTOPLT ALT HOLD DID NOT HOLD THE ALT AT WHICH THE ACFT HAD LEVELED OFF TO AFTER CLB.

Narrative: WE WERE LEVELING OFF FROM CLB AT FL310. THE AUTOPLT WAS ENGAGED AND THE ACFT LEVELED OFF AT FL310 AND THEN STARTED TO CLB WITH THE AUTOPLT ON ALT HOLD. WE SPOTTED THE CLB AT ABOUT FL310 AND ROLLED THE AUTOPLT PITCH (VERT SPD) CTL TO DSND. I WAS ABOUT TO DISENGAGE THE AUTOPLT WHEN IT FINALLY RESPONDED TO INPUTS AND LEVELED OFF AND STARTED BACK DOWN TO FL310 MAX. ALT WAS FL313. THE AUTOPLT DID THE SAME THING AGAIN WHEN I LEVELED OFF AT FL310, BUT THIS TIME I DISENGAGED THE AUTOPLT AND TRIMMED ACFT BY HAND. AUTOPLT WORKED NORMALLY AFTER RE- ENGAGEMENT.

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.