B737-200 UNCOMMANDED RUDDER MOVEMENT ON CTL CHK ON TAXI OUT PHX.

Narrative

WHILE STOPPED AND AWAITING FOR TAXI CLRNC FROM THE RAMP; I ACCOMPLISHED A CTL CHK OF THE RUDDER. WHEN THE RUDDER PEDALS WERE RETURNED TO THE NEUTRAL POS; I NOTICED A VIBRATION IN THE AIRFRAME. THINKING IT MIGHT BE ENG BLAST FROM AN ACFT INVISIBLE TO THE COCKPIT; I DECIDED TO TRY AGAIN DURING TAXI OUT. WHEN TAXI CLRNC WAS RECEIVED AND WHILE THE ACFT WAS MOVING; I ONCE AGAIN PERFORMED THE CTL CHK. WITH THE ACFT MOVING; THE VIBRATION WAS MUCH SUBDUED; AND I DOUBT IF I WOULD HAVE NOTICED IT; HAD IT NOT BEEN SO APPARENT WHILE STOPPED. I ONCE AGAIN STOPPED AND REPEATED THE CTL CHK. AGAIN THE VIBRATION WAS OBSERVED WHEN THE RUDDER CTRED. AT THIS TIME I DECIDED TO RETURN TO THE GATE AND DEFER THIS MATTER TO MAINT. WITH A TECHNICIAN OUTSIDE THE AIRPLANE OBSERVING THE RUDDER; THE PEDALS WERE DISPLACED. THE TECHNICIAN NOTED THAT WHEN THE RUDDER RETURNED TO CTR; IT WOULD CONTINUE PAST CTR SEVERAL INCHES AND THEN REVERSE DIRECTION. IT WOULD BYPASS CTR; STOP AND REPEAT THE PROCESS. IT WOULD DO THIS SEVERAL TIMES WITH DECREASING FREQ AND AMPLITUDE BEFORE FINALLY STOPPING. I TURNED OFF THE YAW DAMPER; BUT NO CHANGE WAS NOTED WITH THE VIBRATION. APPARENTLY THIS IS WHAT WAS CAUSING THE SHUDDER I FELT IN THE AIRFRAME. MAINT INDICATED THE PCU HAD RECENTLY BEEN REPLACED AND DECIDED TO REMOVE THE ACFT FROM SVC. LATER DISCUSSION WITH MAINT CTL REVEALED THE LATEST PCU WOULD BE REPLACED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT AT THE TIME OF THE INCIDENT; HE CONTACTED COMPANY AND UNION SAFETY PERSONNEL. THE PCU UNIT HAD BEEN INSTALLED 7 DAYS PREVIOUSLY AND WITH THE MANDATED NEW AND IMPROVED VERSION. THE ACR MAINT PERSONS SENT THE UNIT BACK TO BOEING. THE UNIT WAS BENCH TESTED AT BOEING AND NO FAULT WAS FOUND. BOEING STATED TO THE ACR THAT THE INCIDENT WAS MOST LIKELY A RESULT OF A LINKAGE RIGGING PROB AT THE TIME OF INSTALLATION OF THE NEW UNIT. THE RPTR DISAGREES WITH BOEING'S DIAGNOSIS AND BELIEVES THAT THE BASIC PROB STILL EXISTS. HE FURTHER STATES THAT BOEING IS NOW RECOMMENDING INCREASED FLAPS ZERO TO ONE SPEEDS FROM 210 KIAS TO 220 KIAS AS PROTECTION AGAINST THE HARD OVER. THE RPTR BELIEVES THIS CHANGE TO BE INEFFECTIVE; ESPECIALLY SINCE THE SPEEDS REVERT TO THE OLD VALUES IN THE EVENT OF A SINGLE ENG ON TKOF. THE RPTR WOULD LIKE TO SEE A SPLIT RUDDER SOMEWHAT LIKE THE B727 AS A SAFER AND MORE REASONABLE FIX TO A DANGEROUS SIT. SUPPLEMENTAL INFO FROM ACN 443136: THIS OCCURRED WITH THE YAW DAMPER ON OR OFF. THE ACFT WAS GNDED AND TOWED TO THE HANGAR.