What was found
FLIGHT 2152. DURING FLT HAD TWO EVENTS OF EXCESSIVE RT YAW MOVEMENTS. FIRST EVENT FL280 IN CRUISE FOR ABOUT 5 SECS, EVENT SELF CORRECTED. SECOND EVENT ON INITIAL DESCENT SUDDEN MOVEMENT TO RT. LASTED 2-3 MINUTES. AP WAS MANUALLY DISCONNECTED & YAW TRIM USED. USED ABOUT 3/4 OF TRIM TO LT. EVENT CORRECTED SLOWLY AND TRIM WAS NEUTRALIZED. AP ENGAGED BOTH EVENTS. PFD INDICATION SHOWED FULL DEFLECTION TO LT. TURBULANCE NILL/ CROSSWIND UNKOWN. LANDING UNEVENTFUL. REMOVED FROM SERVICE. REPLACED UPPER RUDDER PCU. REF LOGPAGE 1152017 FOR OPS CHKD FLT RELEASE. FLIGHT PASSED. RETURNED TO SERVICE.