As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS IN DECENT, WHEN PILOT INPUTTED 1/4 TO 1/2 INCH MOVEMENT OF THE CONTROL WHEEL, CONTROLS BECAME LIGHT FOLLOWED BY THE AIRCRAFT SHAKING VIOLENTLY. THE CONTROL YOKE FLUCTUATED BETWEEN FULL FORWARD AND FULL AFT REQUIRING BOTH PILOT AND INSTRUCTOR PILOT TO HOLD THE CONTROL YOKE TO REGAIN CONTROL OF THE AIRCRAFT. LANDED WITHOUT FURTHER INCIDENT AND UPON EXITING THE AIRCRAFT FOUND THE TRIM TAB CONTROL TUBE SHEARED IN HALF.