AN MLG EXPERIENCES A RUNAWAY RUDDER TRIM DURING INITIAL CLB.

Narrative

I WAS CAPT OF MLG NON STOP LAX-BWI. FO MADE THE TKOF. AT APPROX 1000 FT MSL; WHILE I WAS SWITCHING TO DEP CTL; I FELT THE ACFT YAW. AT FIRST I THOUGHT IT WAS WAKE TURB; THEN I CHKED THE ENG INSTS (NORMAL); THEN I CHKED THE RUDDER TRIM. I SAW THE RUDDER TRIM INDICATOR MOVING PAST 9 UNITS R TRIM. I GRABBED THE RUDDER TRIM CTL KNOB AND COMMANDED THE RUDDER BACK TO NEUTRAL. THE RUDDER RESPONDED AND WENT BACK TO NEUTRAL. THE FO HAND FLEW THE ACFT TO FL230 WHERE WE ENGAGED THE AUTOPLT AND PULLED THE RUDDER TRIM CTL CIRCUIT BREAKER. NO FURTHER PROBS WERE NOTED AND WE CONTINUED TO BWI AND WROTE UP THE RUDDER TRIM. OUR ACFT WAS AN ORIGINATOR IN LAX. I PERFORMED A RUDDER TRIM CHK PRIOR TO ENG START AND A FLT CTL CHK PRIOR TO TKOF. BOTH CHKS WERE NORMAL IN ALL RESPECTS. NO RUDDER TRIM KNOB STICKING WAS NOTED. NO RUDDER TRIM INPUTS WERE MADE BY EITHER PLT PRIOR TO THE TRIM RUNNING AWAY. I DO NOT BELIEVE THIS PROB WAS CAUSED BY A STICKING KNOB. I WONDER IF THIS IS IN ANY WAY RELATED TO THE LGA ACCIDENT. I KNOW MOST OF US FLYING THIS ACFT WOULD PREFER THE OLD MECHANICAL RUDDER TRIM SYS THAT IS ON THE MLG.