As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT CREW REPORTED MOMENTARY PITCH TRIM RUNAWAY ON CLIMBOUT AT FL260. NOSE DOWN FOR APPROXIMATELY 2 SECONDS. BACK PRESSURE WAS APPLIED TO COUNTER TRIM AND NOSE UP ELECTRIC TRIM WAS SELECTED AND TRIM STOPPED. AUTO PILOT WAS OFF. REPLACED STABILIZER TRIM ACTUATOR AND R64 RELAY, PERFORMED OPERATIONAL TEST AND CHECKED OKAY.