Narrative:

During taxi I noticed the rudder trim indicator moving 5 degree either side of zero trim position. I reset the rudder trim indicator circuit breaker and the trim indicator moved to zero trim. I wrote the problem in the aircraft's logbook. Maintenance also noticed the same indication movements while aircraft sitting at the gate. They did not have the parts to repair it, so they MEL'ed the system. I complained that this was still unsafe should I receive an uncommanded input to the rudder trim, I would have no indication unless my feet were on the rudder pedals when they moved. The mechanic stated this was a FAA approved procedure. Considering the accident that occurred in lga regarding the rudder trim, I was quite surprised the FAA would allow an aircraft to dispatch with the rudder trim indicator inoperative. I have since contacted my local air safety representative and informed him that this problem needs to be addressed. The company was also notified. Takeoff with an undetected rudder trim in an extreme left or right position would be disastrous. Callback conversation with reporter revealed following information. The hazard for in-flight as I see it is that if a runway rudder trim occurred in flight the first indication would be when the autoplt tripped off because of too much rudder input and the aircraft might become, at least momentarily, uncontrollable. It is probable that the flight crew would not notice the indicator moving until they did detect a control problem even if it (right trim indicator) was operating normally. The only input to cause a runaway rudder would be a spurious signal of some kind that maintenance says could never happen but I believe anything electrically controled can do the impossible at the most embarrassing time. I have taken the MEL to company and my safety representative and it is being discussed and reexamined.

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Original NASA ASRS Text

Title: MLG ACFT RUDDER TRIM INDICATOR INOPERATIVE. ACFT DISPATCHED PER MEL WITH INDICATOR INOPERATIVE.

Narrative: DURING TAXI I NOTICED THE RUDDER TRIM INDICATOR MOVING 5 DEG EITHER SIDE OF ZERO TRIM POS. I RESET THE RUDDER TRIM INDICATOR CB AND THE TRIM INDICATOR MOVED TO ZERO TRIM. I WROTE THE PROB IN THE ACFT'S LOGBOOK. MAINT ALSO NOTICED THE SAME INDICATION MOVEMENTS WHILE ACFT SITTING AT THE GATE. THEY DID NOT HAVE THE PARTS TO REPAIR IT, SO THEY MEL'ED THE SYS. I COMPLAINED THAT THIS WAS STILL UNSAFE SHOULD I RECEIVE AN UNCOMMANDED INPUT TO THE RUDDER TRIM, I WOULD HAVE NO INDICATION UNLESS MY FEET WERE ON THE RUDDER PEDALS WHEN THEY MOVED. THE MECH STATED THIS WAS A FAA APPROVED PROC. CONSIDERING THE ACCIDENT THAT OCCURRED IN LGA REGARDING THE RUDDER TRIM, I WAS QUITE SURPRISED THE FAA WOULD ALLOW AN ACFT TO DISPATCH WITH THE RUDDER TRIM INDICATOR INOP. I HAVE SINCE CONTACTED MY LCL AIR SAFETY REPRESENTATIVE AND INFORMED HIM THAT THIS PROB NEEDS TO BE ADDRESSED. THE COMPANY WAS ALSO NOTIFIED. TKOF WITH AN UNDETECTED RUDDER TRIM IN AN EXTREME L OR R POS WOULD BE DISASTROUS. CALLBACK CONVERSATION WITH RPTR REVEALED FOLLOWING INFO. THE HAZARD FOR INFLT AS I SEE IT IS THAT IF A RWY RUDDER TRIM OCCURRED IN FLT THE FIRST INDICATION WOULD BE WHEN THE AUTOPLT TRIPPED OFF BECAUSE OF TOO MUCH RUDDER INPUT AND THE ACFT MIGHT BECOME, AT LEAST MOMENTARILY, UNCONTROLLABLE. IT IS PROBABLE THAT THE FLT CREW WOULD NOT NOTICE THE INDICATOR MOVING UNTIL THEY DID DETECT A CONTROL PROB EVEN IF IT (R TRIM INDICATOR) WAS OPERATING NORMALLY. THE ONLY INPUT TO CAUSE A RUNAWAY RUDDER WOULD BE A SPURIOUS SIGNAL OF SOME KIND THAT MAINT SAYS COULD NEVER HAPPEN BUT I BELIEVE ANYTHING ELECTRICALLY CTLED CAN DO THE IMPOSSIBLE AT THE MOST EMBARRASSING TIME. I HAVE TAKEN THE MEL TO COMPANY AND MY SAFETY REPRESENTATIVE AND IT IS BEING DISCUSSED AND REEXAMINED.

Data retrieved from NASA's ASRS site as of July 2007 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.