As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNCOMMANDED RUDDER FLUCTUATION IN FLIGHT WITH BOTH AUTOPILOT AND YAW DAMPNER ON OR OFF. WHEN ON THE GROUND CREW NOTICED THE PEDALS WERE PULSATING EVERY COUPLE SECONDS WITH NO HYD PRESSURE ON THE SYSTEM. DECLARED AN EMERGENCY AND RETURNED TO THE FIELD. PULLED FDR. OPEN