AILERON TRIM FAILURE. THE TRIM WOULD ONLY TRIM IN ONE DIRECTION. CREATED EXTRA FORCE ON THE CTLS. MECH SUSPECTS FAULTY RELAY.

Narrative

AT ABOUT 11 MINS INTO THE FLT; AFTER AN UNEVENTFUL TKOF AND DEP; AND ESTABLISHED AT CRUISE; THE AUTOMATIC FLT CTL SYS GAVE US A ROLL L WING DOWN MESSAGE. CAPT REACTED BY DISENGAGING THE AUTOPLT AND ADDED L AILERON AND RUDDER TRIM. UPON RE-ENGAGING THE AUTOPLT THE ACFT WAS STILL OUT OF TRIM; SO ADDITIONAL AILERON TRIM WAS ADDED. IN THE PROCESS OF ADDING THE ADDITIONAL AILERON TRIM; CAPT NOTICED THAT HE WAS UNABLE TO DECREASE TRIM AND ASKED ME MY OBSERVATION. INITIALLY; I NOTICED THAT IT WAS INTERMITTENTLY WORKING PROPERLY; BUT FOR THE MOST PART WOULD GIVE ONLY L WING DOWN TRIM. HE GAVE ME THE CTLS; AND I TRIED THEM MYSELF. I WAS ALSO UNABLE TO DECREASE L AILERON TRIM. AT THIS POINT CAPT LOOKED AT THE ABNORMAL CHKLISTS REGARDING AILERON MISTRIM AND AILERON JAM MALFUNCTIONS AND SURMISED THAT THERE WAS NOTHING ELSE WE COULD DO BUT CONTINUE ON FLYING THE ACFT MANUALLY. HE THEN TOOK BACK THE CTL OF THE ACFT AND TOLD ME TO LOOK AT THE ABNORMAL CHKLIST. I DREW THE SAME CONCLUSION. HE ALSO ADVISED ME TO TRY TO RECYCLE THE APPROPRIATE CIRCUIT BREAKERS; WHICH DID NOT REMEDY THE PROB. SINCE WE WERE PAST THE HALFWAY POINT AND IN RANGE OF KAHULUI WE CONTINUED THE FLT WITH CAPT AT THE CTLS OF THE ACFT. THE REMAINDER OF THE FLT WAS UNEVENTFUL. WHILE THE MECH WAS TRYING TO FIX THE ACFT WE WERE ABLE TO GET THE TRIM TO READ WINGS LEVEL. THE MECH PROCEEDED TO CHK THE AILERONS AND THE RESPECTIVE TRIM TABS TO MAKE SURE TRIMS WERE ZERO AND NO JAMS HAD OCCURRED. AT THIS POINT WE DECIDED TO FLY THE ACFT BACK WITHOUT AUTOPLT AND WITHOUT THE AILERON TRIM FUNCTION. AFTER OBTAINING THE APPROPRIATE PERMITS AND SIGNOFFS WE BROUGHT THE ACFT BACK TO HNL WITH CAPT AT THE CTLS. THE FLT WAS UNEVENTFUL. IN RETROSPECT I FEEL THAT WE SHOULD HAVE NOTIFIED ATC OF OUR PROB AND RETURNED TO HNL IMMEDIATELY AFTER THE PROB HAD OCCURRED; INSTEAD OF CONTINUING TO KAHULUI WHILE DEALING WITH THE PROB. SECONDLY; AFTER LNDG AT KAHULUI THE ACFT SHOULD NOT HAVE BEEN FLOWN BACK UNTIL THE ACFT WAS REPAIRED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE AILERON TRIM IS ELECTRICAL ON THIS ATR42-300. WHEN THE AFCS (AUTOMATIC FLT CTL SYS) GAVE A WING DOWN MESSAGE; THE CAPT DISENGAGED THE AUTOPLT AND ADDED L AILERON AND RUDDER TRIM; BUT WHEN RE-ENGAGING THE AUTOPLT; IT WAS STILL OUT OF TRIM; SO MORE TRIM WAS ADDED. IT WAS THEN NOTICED THAT THE TRIM COULD NOT BE DECREASED (TRIMMED THE OPPOSITE DIRECTION). SINCE THERE WAS NO IRREGULAR OR EMER CHKLIST ASSOCIATED WITH THAT PROB; THE FLC CONTINUED TO FLY MANUALLY WITHOUT USING THE AILERON TRIM. BECAUSE THE TRIM WAS DISPLACED; IT TOOK GREATER CTL FORCE TO FLY THE ACFT MANUALLY TO COUNTERACT THE TRIM. SINCE RUDDER TRIM IS USED MUCH MORE; PARTICULARLY WITH PWR CHANGES; IT HELPED TO COUNTER THE OFFSET AILERON. AFTER LNDG; THE MECH WAS ABLE TO GET THE TRIM BACK TO ZERO AND HE SURMISED THAT THE PROB OF 1-WAY AILERON TRIM WAS DUE TO A FAULTY RELAY. THE FLC DECIDED TO FLY THE ACFT BACK TO HNL. RPTR FO HAD NOT HEARD OF ANY SIMILAR PROBS WITH THE ATR42 AILERON TRIM; BUT HE HAD HEARD OF A SIMILAR PROB WITH THE HORIZ STABILIZER TRIM.