As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT NR 6170 - IAD-EWR - DURING CRUISE, RETURNED TO IAD DUE TO VIBRATION BEING EXPERIENCED FROM THE RUDDER. AIRCRAFT LANDED AT IAD WITH NO FURTHER INCIDENTS. MAINTENANCE REPLACED THE RUDDER TRIM TAB BEARINGS. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (M)