Narrative:

Aircraft had just come out of annual and was returning to ZZZ to ZZZ1. All systems including trim; flaps; cowl flaps; flight controls; autopilot and avionics tested fully functional prior to departure. Entire flight and descent for landing went normally; however after extending flaps for landing; manual or electric trim control would not allow trim position to budge from cruise position. Control forces were far too great to allow a safe landing on a narrow 3;200 ft. Runway in 20+ kt. Gusts. Completed a missed approach and attempted a second landing but trim was still frozen. Missed the approach a second time and climbed to 5;000 ft. To troubleshoot. Contacted service facility by phone while informing ATC of the problem. When it was clear that further trouble shooting was useless and fuel was down to landing reserves (1 hour remaining); [requested priority handling] and requested vectors to wide 6;100 ft. Runway at ZZZ2 (10 miles away) for landing. Determined that considerable control force could be alleviated if I landed without flaps and at vref +15. Landing was smooth and safe after aircraft floated about 4;000 ft. Because of higher than normal speed. After landing a maintenance technician removed the front belly panel and found FOD that had dropped down from the cockpit opening in the trim housing to the trim chain below. The FOD blocked the sprocket from turning the chain and made trim adjustment impossible. Since the plane was in light turbulence for most of the flight; the FOD most probably shifted from an undetectable benign position to a highly dangerous one. Maintenance shop is now removing the trim cover during all annual inspections to check for FOD.

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Original NASA ASRS Text

Title: Pilot reported that a trim malfunction resulted in a diversion.

Narrative: Aircraft had just come out of annual and was returning to ZZZ to ZZZ1. All systems including trim; flaps; cowl flaps; flight controls; autopilot and avionics tested fully functional prior to departure. Entire flight and descent for landing went normally; however after extending flaps for landing; manual or electric trim control would not allow trim position to budge from cruise position. Control forces were far too great to allow a safe landing on a narrow 3;200 ft. runway in 20+ kt. gusts. Completed a missed approach and attempted a second landing but trim was still frozen. Missed the approach a second time and climbed to 5;000 ft. to troubleshoot. Contacted service facility by phone while informing ATC of the problem. When it was clear that further trouble shooting was useless and fuel was down to landing reserves (1 hour remaining); [requested priority handling] and requested vectors to wide 6;100 ft. Runway at ZZZ2 (10 miles away) for landing. Determined that considerable control force could be alleviated if I landed without flaps and at Vref +15. Landing was smooth and safe after aircraft floated about 4;000 ft. because of higher than normal speed. After landing a Maintenance Technician removed the front belly panel and found FOD that had dropped down from the cockpit opening in the trim housing to the trim chain below. The FOD blocked the sprocket from turning the chain and made trim adjustment impossible. Since the plane was in light turbulence for most of the flight; the FOD most probably shifted from an undetectable benign position to a highly dangerous one. Maintenance shop is now removing the trim cover during all annual inspections to check for FOD.

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.