Narrative:

Upon descent and after cancelling an IFR flight plan with approach; an elevator trim issue was encountered. While performing a maintenance flight on the aircraft up to fl 280; the pilot flying (PF) climbed up to fl 280 using manual controls including trim actuation. After the flight test; the PF was descending with the autopilot on from FL280 to 15;000 and then from 15;000 to 8;000. While in the descent the PF and pilot not flying (PNF) were being told to trim down by the autopilot voice for the latter half of the descent. The PF had been trimming the airplane.before the plane leveled off at the scheduled 8;000; the plane abruptly pitched up. When the (PNF) grabbed the controls he was able to push the nose down but it was very heavy. The PNF then said 'my airplane' and took control of the airplane. (The PF had less than 2 hours in the plane) the now new PF simultaneously tried to trim the nose down when pushing forward but the trim was not working. The PF then turned the trim switch off. The PF landed the airplane. On the way to landing the PF pulled the breaker for the trim upon the suggestion from the previous PF now PNF. The trim situation never got worse from the initial pitch up. After the initial pitch up; engine and control monitor was indicating full right aileron trim (all the way down the trim indicator) all the way nose down elevator trim was indicated as well. The PF and PNF did not have an aileron trim problem in the controls.the PF and PNF worked together to run checklists and to relieve each other of the opposing elevator control.after landing; the trim and trim switch were reset. [The engine and control monitor] then indicated normal aileron trim and elevator trim where it should have been for what the PF and PNF felt which was full nose up; the trim also worked again after was reset.there were no injuries or damage.

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Original NASA ASRS Text

Title: The electric trim ran nose up with autopilot on. The aircrew overrode the system by disconnecting it.

Narrative: Upon descent and after cancelling an IFR flight plan with Approach; an elevator trim issue was encountered. While performing a maintenance flight on the aircraft up to FL 280; the Pilot Flying (PF) climbed up to FL 280 using manual controls including trim actuation. After the flight test; the PF was descending with the autopilot on from FL280 to 15;000 and then from 15;000 to 8;000. While in the descent the PF and Pilot Not Flying (PNF) were being told to trim down by the autopilot voice for the latter half of the descent. The PF had been trimming the airplane.Before the plane leveled off at the scheduled 8;000; the plane abruptly pitched up. When the (PNF) grabbed the controls he was able to push the nose down but it was very heavy. The PNF then said 'my airplane' and took control of the airplane. (the PF had less than 2 hours in the plane) The now new PF simultaneously tried to trim the nose down when pushing forward but the trim was not working. The PF then turned the trim switch off. The PF landed the airplane. On the way to landing the PF pulled the breaker for the trim upon the suggestion from the previous PF now PNF. The trim situation never got worse from the initial pitch up. After the initial pitch up; engine and control monitor was indicating full right Aileron trim (all the way down the trim indicator) all the way nose down elevator trim was indicated as well. The PF and PNF did not have an aileron trim problem in the controls.The PF and PNF worked together to run checklists and to relieve each other of the opposing elevator control.After landing; the trim and trim switch were reset. [The engine and control monitor] then indicated normal aileron trim and elevator trim where it should have been for what the PF and PNF felt which was full nose up; the trim also worked again after was reset.There were no injuries or damage.

Data retrieved from NASA's ASRS site 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.