As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RUDDER PEDALS WERE STIFF DURING CONTROL CHECK, ON CLIMB OUT OF ICT. CLIMBING TO FL 350, AIRCRAFT STARTED TO YAW AND DUTCH ROLL. DISCONNECTED AUTO PILOT. TURNING OFF YAW DAMPER AND GOING TO MANUAL RUDDER DID NOT STOP YAW/DUTCH ROLL. AIRCRAFT SLOWED AND DESCENDED TO 280 FOR REMAINDER OF FLIGHT. FOUND RUDDER POWER CONTROL ACTUATOR ASSEMBLY BY-PASSING HYDRAULIC FLUID. REPLACED THE CONTROL ACTUATOR ASSEMBLY IAW DC-9 AMM 27-20-06-4-0002.