B737NG captain reported that he did not have rudder authority when he used the rudder standby system...

Attributes
ACN	1500361
Time
Date	201711
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Parked
Flight Plan	IFR
Component
Aircraft Component	Rudder Control System
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

Narrative:

We arrived for an aircraft swap early. During my (captain) preflight flow I always check the standby rudder. As I selected standby rudder the standby rudder light illuminated as normal but I had no rudder authority; when I moved to switch back to normal the standby rudder on light remained illuminated. Maintenance was called and replaced the overhead module to see if it was an electrical issue. With no change the aircraft was taken out of service. I spoke with two instructors and was told this was not the first occurrence of this problem. I'm concerned to think about the aircraft potentially flying for a period of time before we discovered the problem.put this check back into our preflight flow.

Original NASA ASRS Text

Title: B737NG Captain reported that he did not have rudder authority when he used the rudder standby system.

Narrative: We arrived for an aircraft swap early. During my (Captain) preflight flow I always check the standby rudder. As I selected standby rudder the Standby Rudder light illuminated as normal but I had no rudder authority; when I moved to switch back to normal the Standby Rudder on light remained illuminated. Maintenance was called and replaced the overhead module to see if it was an electrical issue. With no change the aircraft was taken out of service. I spoke with two instructors and was told this was not the first occurrence of this problem. I'm concerned to think about the aircraft potentially flying for a period of time before we discovered the problem.Put this check back into our preflight flow.

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.