Narrative:

I experienced a left aircraft yaw at approximately 6700 ft MSL. The engines were normal and the yaw damper was turned off. The first officer noticed that the rudder trim indicated full left trim with the control knob centered. The first officer centered the rudder trim while I controled the aircraft. We returned to charlotte and made an uneventful landing on runway 18R. Callback conversation with reporter revealed the following: the captain was hand flying the aircraft during the climb out. At 6700 ft MSL he found that he had to push some rudder in on the right pedal to keep the aircraft going straight. He checked the engines and they were producing balanced power so he told the first officer about the problem and requested a level off at 7000 ft. While they were level they started an analysis of the problem. The first officer verified that the engines, flight controls and fuel were in a balanced condition and turned off the yaw damper as per procedure. The flight crew discussed turning off the hydraulic power to the flight controls, but decided not to do that. A few seconds later the first officer noticed the rudder trim was fully deflected to the left and with the captain's concurrence slowly centered it. The flight crew decided to return and land at clt. Maintenance decided to remove the entire rudder trim mechanism from the aircraft for a detailed examination. The flight crew has been interviewed by a number of different people from several organizations and the quip testing is ongoing. A B737-400 captain for another air carrier was on board and he reported that the yaw movement was very noticeable to him and the passenger. The flight attendants were informed of the situation by the flight crew as soon as they had the aircraft under control and the attendants also reported the noticeable yaw. The noticeable yaw occurred during power reduction after leveling at 7000 ft. The captain attempted to bring the throttles back smoothly together while adjusting his rudder inputs to the new flight dynamics for the B737-300, but admitted that he could have been more precise with practice in this confign.

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Original NASA ASRS Text

Title: ACFT EQUIP PROB - ACR RUDDER TRIM SYS HAD AN UNCOMMANDED FULL L TRIM INPUT DURING CLBOUT.

Narrative: I EXPERIENCED A L ACFT YAW AT APPROX 6700 FT MSL. THE ENGS WERE NORMAL AND THE YAW DAMPER WAS TURNED OFF. THE FO NOTICED THAT THE RUDDER TRIM INDICATED FULL L TRIM WITH THE CTL KNOB CTRED. THE FO CTRED THE RUDDER TRIM WHILE I CTLED THE ACFT. WE RETURNED TO CHARLOTTE AND MADE AN UNEVENTFUL LNDG ON RWY 18R. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE CAPT WAS HAND FLYING THE ACFT DURING THE CLB OUT. AT 6700 FT MSL HE FOUND THAT HE HAD TO PUSH SOME RUDDER IN ON THE R PEDAL TO KEEP THE ACFT GOING STRAIGHT. HE CHKED THE ENGS AND THEY WERE PRODUCING BALANCED PWR SO HE TOLD THE FO ABOUT THE PROB AND REQUESTED A LEVEL OFF AT 7000 FT. WHILE THEY WERE LEVEL THEY STARTED AN ANALYSIS OF THE PROB. THE FO VERIFIED THAT THE ENGS, FLT CTLS AND FUEL WERE IN A BALANCED CONDITION AND TURNED OFF THE YAW DAMPER AS PER PROC. THE FLC DISCUSSED TURNING OFF THE HYD PWR TO THE FLT CTLS, BUT DECIDED NOT TO DO THAT. A FEW SECONDS LATER THE FO NOTICED THE RUDDER TRIM WAS FULLY DEFLECTED TO THE L AND WITH THE CAPT'S CONCURRENCE SLOWLY CTRED IT. THE FLC DECIDED TO RETURN AND LAND AT CLT. MAINT DECIDED TO REMOVE THE ENTIRE RUDDER TRIM MECHANISM FROM THE ACFT FOR A DETAILED EXAMINATION. THE FLC HAS BEEN INTERVIEWED BY A NUMBER OF DIFFERENT PEOPLE FROM SEVERAL ORGANIZATIONS AND THE QUIP TESTING IS ONGOING. A B737-400 CAPT FOR ANOTHER ACR WAS ON BOARD AND HE RPTED THAT THE YAW MOVEMENT WAS VERY NOTICEABLE TO HIM AND THE PAX. THE FLT ATTENDANTS WERE INFORMED OF THE SIT BY THE FLC AS SOON AS THEY HAD THE ACFT UNDER CTL AND THE ATTENDANTS ALSO RPTED THE NOTICEABLE YAW. THE NOTICEABLE YAW OCCURRED DURING PWR REDUCTION AFTER LEVELING AT 7000 FT. THE CAPT ATTEMPTED TO BRING THE THROTTLES BACK SMOOTHLY TOGETHER WHILE ADJUSTING HIS RUDDER INPUTS TO THE NEW FLT DYNAMICS FOR THE B737-300, BUT ADMITTED THAT HE COULD HAVE BEEN MORE PRECISE WITH PRACTICE IN THIS CONFIGN.

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.