Narrative:

On climb out passing FL330, autoplt trim light came on. I disconnected autoplt and found aircraft out of trim. I retrimmed aircraft and leveled off at FL350. Autoplt was re- engaged and seemed to be doing fine. 20 mins later at FL350 trim movement was indicated by aural cockpit warning. I observed the aircraft in a 1500 FPM climb and passing 35300 ft. I disconnected the autoplt and topped the climb at 700 ft high (35700 ft). Flight director was giving fly-down commands through the maneuver. Suspect autoplt trim ran nose up. ZTL asked if we were still at FL350 and we told them we were getting there at that time. After leveloff autoplt was re-engaged and observed to be cycling plus or minus 75-100 ft. Switched to other autoplt and it was doing much better. No deviations were observed and the flight was continued using that autoplt with no further incidents. Aircraft was written up in dallas and the problem corrected by not considering that autoplt usable until it could be corrected/replaced. Supplemental information from acn 304390: aircraft gained approximately 700 ft in altitude. TCASII advisory went off at approximately FL355. Climb was discovered by altitude warning activating at 35250 ft. FMS remained in VNAV level the entire time. At the time we were involved in deviating around thunderstorms. My attention was devoted to the WX radar tuning and failed to catch the departure until the altitude deviation. Our altimeter warnings are set fleetwide at 250 ft. I believe it would be helpful if they were reset to plus or minus 100 ft.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION AFTER ACFT EXPERIENCES AN ACFT EQUIP PROB.

Narrative: ON CLBOUT PASSING FL330, AUTOPLT TRIM LIGHT CAME ON. I DISCONNECTED AUTOPLT AND FOUND ACFT OUT OF TRIM. I RETRIMMED ACFT AND LEVELED OFF AT FL350. AUTOPLT WAS RE- ENGAGED AND SEEMED TO BE DOING FINE. 20 MINS LATER AT FL350 TRIM MOVEMENT WAS INDICATED BY AURAL COCKPIT WARNING. I OBSERVED THE ACFT IN A 1500 FPM CLB AND PASSING 35300 FT. I DISCONNECTED THE AUTOPLT AND TOPPED THE CLB AT 700 FT HIGH (35700 FT). FLT DIRECTOR WAS GIVING FLY-DOWN COMMANDS THROUGH THE MANEUVER. SUSPECT AUTOPLT TRIM RAN NOSE UP. ZTL ASKED IF WE WERE STILL AT FL350 AND WE TOLD THEM WE WERE GETTING THERE AT THAT TIME. AFTER LEVELOFF AUTOPLT WAS RE-ENGAGED AND OBSERVED TO BE CYCLING PLUS OR MINUS 75-100 FT. SWITCHED TO OTHER AUTOPLT AND IT WAS DOING MUCH BETTER. NO DEVS WERE OBSERVED AND THE FLT WAS CONTINUED USING THAT AUTOPLT WITH NO FURTHER INCIDENTS. ACFT WAS WRITTEN UP IN DALLAS AND THE PROB CORRECTED BY NOT CONSIDERING THAT AUTOPLT USABLE UNTIL IT COULD BE CORRECTED/REPLACED. SUPPLEMENTAL INFO FROM ACN 304390: ACFT GAINED APPROX 700 FT IN ALT. TCASII ADVISORY WENT OFF AT APPROX FL355. CLB WAS DISCOVERED BY ALT WARNING ACTIVATING AT 35250 FT. FMS REMAINED IN VNAV LEVEL THE ENTIRE TIME. AT THE TIME WE WERE INVOLVED IN DEVIATING AROUND TSTMS. MY ATTN WAS DEVOTED TO THE WX RADAR TUNING AND FAILED TO CATCH THE DEP UNTIL THE ALTDEV. OUR ALTIMETER WARNINGS ARE SET FLEETWIDE AT 250 FT. I BELIEVE IT WOULD BE HELPFUL IF THEY WERE RESET TO PLUS OR MINUS 100 FT.

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.