Narrative:

During early climb I noted that the rudder trim knob, at different times, did not return to the neutral position. The knob would remain hard over, left or right, depending on which way it was turned, until you returned it to the neutral position. This occurred during cruise also. After landing at den we placed the knob hard right and the rudder indice moved right until 10-12 units before it released and returned to the neutral position. We tried it several more times but the knob problem was not consistent and did not repeat its malfunction each time it was turned. I suspect the base of the knob is mounted too close to the surface under, causing it to bind on dirt, debris, lint, etc, that accumulated between the 2 surfaces. Cockpits are not the cleanest part of the aircraft. Operationally I would recommend that crews not let go of that knob until they feel it return to the neutral position and visually check to make sure it has returned to the neutral position. From a maintenance standpoint, I would suggest periodic checks to ascertain freedom of movement of the knob after being turned and then released. Height adjustment is critical as is the cleanliness of the surface below the knob. I think these 2 steps, proper cleaning and proper height adjustment, would solve the problem. Again, as with air carrier accident at lga, this small knob moved and monitored prior to takeoff could cause a hand full of problems running down a runway.

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Original NASA ASRS Text

Title: ACR MLG RUDDER TRIM KNOB BINDING ON PEDESTAL.

Narrative: DURING EARLY CLB I NOTED THAT THE RUDDER TRIM KNOB, AT DIFFERENT TIMES, DID NOT RETURN TO THE NEUTRAL POS. THE KNOB WOULD REMAIN HARD OVER, LEFT OR RIGHT, DEPENDING ON WHICH WAY IT WAS TURNED, UNTIL YOU RETURNED IT TO THE NEUTRAL POS. THIS OCCURRED DURING CRUISE ALSO. AFTER LNDG AT DEN WE PLACED THE KNOB HARD RIGHT AND THE RUDDER INDICE MOVED RIGHT UNTIL 10-12 UNITS BEFORE IT RELEASED AND RETURNED TO THE NEUTRAL POS. WE TRIED IT SEVERAL MORE TIMES BUT THE KNOB PROB WAS NOT CONSISTENT AND DID NOT REPEAT ITS MALFUNCTION EACH TIME IT WAS TURNED. I SUSPECT THE BASE OF THE KNOB IS MOUNTED TOO CLOSE TO THE SURFACE UNDER, CAUSING IT TO BIND ON DIRT, DEBRIS, LINT, ETC, THAT ACCUMULATED BTWN THE 2 SURFACES. COCKPITS ARE NOT THE CLEANEST PART OF THE ACFT. OPERATIONALLY I WOULD RECOMMEND THAT CREWS NOT LET GO OF THAT KNOB UNTIL THEY FEEL IT RETURN TO THE NEUTRAL POS AND VISUALLY CHK TO MAKE SURE IT HAS RETURNED TO THE NEUTRAL POS. FROM A MAINT STANDPOINT, I WOULD SUGGEST PERIODIC CHKS TO ASCERTAIN FREEDOM OF MOVEMENT OF THE KNOB AFTER BEING TURNED AND THEN RELEASED. HEIGHT ADJUSTMENT IS CRITICAL AS IS THE CLEANLINESS OF THE SURFACE BELOW THE KNOB. I THINK THESE 2 STEPS, PROPER CLEANING AND PROPER HEIGHT ADJUSTMENT, WOULD SOLVE THE PROB. AGAIN, AS WITH ACR ACCIDENT AT LGA, THIS SMALL KNOB MOVED AND MONITORED PRIOR TO TKOF COULD CAUSE A HAND FULL OF PROBS RUNNING DOWN A RWY.

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.