AN ACR FREIGHTER CREW NOTICES UNUSUAL YAW MOMENTS DURING TURNS WITH FLAPS EXTENDED AND DURING GND TESTS OF THE RUDDER YAW DAMPER SYS. AFTER A NUMBER OF TESTS AND REPAIRS MAINT REPLACED THE ENTIRE RUDDER PWR CTL UNIT.

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INBOUND TO COS NOTICED ABNORMAL YAW WITH FLAPS EXTENDED AND IN A TURN UPON LEVEL OUT (WINGS) UNCOMMANDED YAW (RUDDER) IN OPPOSITE DIRECTION OF TURN. MADE ACFT MAINT LOG WRITE-UP UPON ARR IN COS IN THE MORNING. AML SIGNED OFF AS R&R COULD NOT DUPLICATE. ON DEP FROM COS SAME PROB NOTED -- UNCOMMANDED YAW BUT THIS TIME BOTH DIRECTIONS FOR APPROX 10 SECONDS AFTER THE TURN WAS COMPLETED. RETRACTED FLAPS BEFORE MAKING ANY TURNS. AT FLAP EXTENSION SAME PROB -- TURNED OFF LOWER YAW DAMPER; PROB WENT AWAY; LANDED PHX. PROB MAY NOT HAVE BEEN YAW DAMPER; BUT POSSIBLY RUDDER CTRING UNIT AS RUDDER POS INDICATOR WOULD HUNT BACK AND FORTH AFTER TURN FOR 10 SECONDS. IN PHX LOWER DAMPER DEFERRED BY MAINT CTL PERSONNEL. FLT TO OAK AT FL280 AND 290 KTS AS PER FLT MANUAL RESTR. I FEEL THAT IN THE COMPANY'S HASTE TO STAY ON TIME; THE PROB DID NOT HAVE HIGH PRIORITY AS NOTED BY A WRITE-UP AS SIMPLE AS 'COULD NOT DUPLICATE' WHEN PROB PERSISTED AGAIN ON DEP AND THE IMPORTANCE OF A FLT CTL MALFUNCTION WAS NOT ADDRESSED IN PHX; JUST DEFERRED. I'M SENDING THIS IN; IN LIGHT OF THE PREVIOUS LOSS OF CTL ACCIDENTS; FOR YOUR DATABASE. I DO NOT KNOW HOW TO CONTACT NTSB AND FEEL MY ACR WOULD JUST BURY IF I FILED A FLC SAFETY RPT -- PAST EXPERIENCE! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS FLYING A B727-200 FREIGHTER WHEN THE FLC NOTED SOME UNUSUAL YAWING MOMENTS DURING TURNS; PARTICULARLY WITH THE FLAPS EXTENDED. DURING GND TESTING HE ALSO NOTED UNUSUAL REACTIONS ON THE RUDDER POS INDICATOR. IN THE AIR THE ACFT WOULD YAW IN THE OPPOSITE DIRECTION OF THE TURN AND THE LOWER RUDDER WOULD DEFLECT FULL TRAVEL ON THE RUDDER POS INDICATOR IN THE OPPOSITE DIRECTION TO THE TURN. ON THE GND; DURING TAXI TESTS; THE LOWER RUDDER WOULD GO TO THE EXTREMES OF THE SCALE OPPOSITE TO THE DIRECTION OF THE TURN AND WHEN THE TURN WAS STOPPED THE INDICATOR WOULD SHOW THAT THE RUDDER THEN MOVED IN THE DIRECTION OF THE ORIGINAL TURN FOR 5-10 SECONDS. AFTER NUMEROUS MAINT CHKS AND REPAIR OR REPLACEMENT OF VARIOUS COMPONENTS IN THE RUDDER AND YAW DAMPER SYS THE ENTIRE RUDDER PWR CTL UNIT WAS REPLACED AND THE PROB WAS SOLVED.