B757 captain reported excessive rudder trim inputs were needed during flight.

Attributes
ACN	1641869
Time
Date	201904
Place
Locale Reference	ZZZ.Airport
State Reference	US
Aircraft 1
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	Rudder Control System
Person 1
Function	Captain
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 171 Flight Crew Type 561
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

Narrative:

This jet required 5 units of left rudder trim in level flight. It also required multiple rudder trim adjustments on approach. We wrote this up; and the jet was taken out of service. It was out of service for about three days.turns out the rudder was out of rig; the rudder ratio changer had to be replaced; there was a damaged shear pin in the original rudder ratio changer; the rudder ratio changer input rod had a broken bearing; and the control rod for the upper rudder power control actuator had a broken nut plate and frozen bolt. At least I think that's what happened -- the maintenance history is a little hard to follow -- especially since we no longer have access to the [electronic] logbook!I don't know how long it had been flying around like this; but I wanted to give this some visibility via [safety report] because flight control system malfunctions are rare; at least in my experience. A malfunctioning rudder ratio changer; in the right failure mode; could potentially be catastrophic.

Original NASA ASRS Text

Title: B757 Captain reported excessive rudder trim inputs were needed during flight.

Narrative: This jet required 5 units of left rudder trim in level flight. It also required multiple rudder trim adjustments on approach. We wrote this up; and the jet was taken out of service. It was out of service for about three days.Turns out the rudder was out of rig; the rudder ratio changer had to be replaced; there was a damaged shear pin in the original rudder ratio changer; the rudder ratio changer input rod had a broken bearing; and the control rod for the upper rudder power control actuator had a broken nut plate and frozen bolt. At least I think that's what happened -- the maintenance history is a little hard to follow -- especially since we no longer have access to the [electronic] logbook!I don't know how long it had been flying around like this; but I wanted to give this some visibility via [safety report] because flight control system malfunctions are rare; at least in my experience. A malfunctioning rudder ratio changer; in the right failure mode; could potentially be catastrophic.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.