Narrative:

At XA03Z 75 NM southwest of fsd VOR assigned cruise altitude FL330 and first officer flying with performance cruise mode engaged -- ZMP called to ask our altitude. We were climbing very slowly through FL335 and promptly corrected with vertical speed mode to assigned altitude. FMA indications were not noted. We found the altitude set window on the flight guidance panel reading FL360 and pms plan altitude reading FL360. Pms had been set to FL330 during preflight. Pms plan altitude was reset to FL330 -- but about 30 min later it changed itself to FL350. First officer had reset pms speed to 260 about 5 min prior to event. He reset his VOR about 10 min prior to event. We do not think the altitude set knob was inadvertently touched.

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Original NASA ASRS Text

Title: FLC OF ACR MLG OVERSHOT CRUISE ALT DUE TO A MIS-SET PERFORMANCE MGMNT SYS (PMS).

Narrative: AT XA03Z 75 NM SW OF FSD VOR ASSIGNED CRUISE ALT FL330 AND FO FLYING WITH PERFORMANCE CRUISE MODE ENGAGED -- ZMP CALLED TO ASK OUR ALT. WE WERE CLBING VERY SLOWLY THROUGH FL335 AND PROMPTLY CORRECTED WITH VERT SPD MODE TO ASSIGNED ALT. FMA INDICATIONS WERE NOT NOTED. WE FOUND THE ALT SET WINDOW ON THE FLT GUIDANCE PANEL READING FL360 AND PMS PLAN ALT READING FL360. PMS HAD BEEN SET TO FL330 DURING PREFLT. PMS PLAN ALT WAS RESET TO FL330 -- BUT ABOUT 30 MIN LATER IT CHANGED ITSELF TO FL350. FO HAD RESET PMS SPD TO 260 ABOUT 5 MIN PRIOR TO EVENT. HE RESET HIS VOR ABOUT 10 MIN PRIOR TO EVENT. WE DO NOT THINK THE ALT SET KNOB WAS INADVERTENTLY TOUCHED.

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.