Narrative:

We were on an IFR flight plan. Our flight was interrupted by a rudder trim malfunction at cruise flight. On this day the flight crew met the director of maintenance at the maintenance repair shop located at ZZZ. The aircraft had been in maintenance to repair a flow control valve in the pressurization system. Also; the copilot's panel had been removed to repair a relay for the right pfd. The work had been completed in the early afternoon hours. After a thorough preflight of the aircraft exterior and interior the flight crew accepted the aircraft and the return of aircraft logs with appropriate logbook entries. The flight departed with only the flight crew on board. The entire flight went well; without incident and we had a successful test flight at altitude of all system through all phases of flight. The aircraft arrived at ZZZ1. At ZZZ1 we put on 200 gals of jet-a while waiting 1 hour for the passenger which were returning for a part 91 flight. On the return trip I was flying from the right seat on an IFR flight plan. On departure we noticed; once we activated the autoplt at 2000 ft MSL; there was an amber east on the right side pfd. I disengaged the autoplt and acknowledged the pitch fault from the autoplt. I then hand flew the aircraft and called for the abnormal checks. We proceeded to continue past 10000 ft and then began to troubleshoot during the cruise climb. After reaching a cruise altitude at FL210 we concluded all checklists. After verifying all trim indications and trim position I reengaged the autoplt to see if the aircraft had been re-trimmed properly. After re-engaging we got the amber east on the copilot mfd and the red trim light on the autoplt. We disconnected again then tried duplicating with an autoplt xfer to the pilot side. The problem did not duplicate this time. We continued to hand fly and I took the controls back and flew from the copilot side. While on a vector to the arrival and flying with the autoplt off I noticed the plane was trimmed but was indicating a slightly out of trim yaw indication. I proceeded to disengage the yaw dampener and apply a very slight input to yaw the nose slightly right. Upon engaging the rudder trim control panel the aircraft went to 60% left trim; yawing the aircraft left; causing me to immediately go to the msw (master thumb switch) and hold the control switch down which temporarily disconnected. The captain then took the controls in the pilot seat and we acknowledged we were completely out of trim. To confirm the situation the captain momentarily released the msw switch while we both kept heavy pressure on the right rudder pedal and his l-hand held the yaw trim circuit breaker. He confirmed the rudder control panel had been in the center position; but when he released the msw the plane continued to yaw further and then he repressed the msw switch and simultaneously pulled the yaw trim circuit breaker. We had verified control of the aircraft and declared an emergency advising we are pan-pan with rudder trim malfunction; have regained control and needed altitude discretion and vectors to ZZZ2 due to WX. We slowed down the aircraft and went through the emergency checklist. We managed to isolate all issues to the rudder trim and decided to fix in order to avoid landing with an asymmetric thrust or in a severe slip condition. While descending we pushed the yaw trim breaker and reapplied the rudder trim controller to center the yaw trim forces. This worked and then we disengaged the yaw trim breaker and monitored all trim functions closely while the captain hand flew the aircraft. We landed safely at ZZZ2 with all passenger and crew ok. I believe the determining factor that allowed this flight crew to respond quickly and accurately came from good simulator training and good CRM in an emergency situation. This led to efficient troubleshooting and corrections. There was complete agreement from both crew members on the emergency situation followed by the corrective action. This is an incredible learning experience and we all hope to never have to duplicate in actual flight conditions. Callback conversation with reporter revealed the following information: reporter stated that lear aircraft uses the terminology 'yaw trim ' and 'yaw trim controller' instead of 'rudder trim' or 'rudder trim control.' the terms are used interchangeably in the text of his report and apply to the same system; which is trim control of the rudder. This rudder system has an electric controlled rudder trim tab on the lower part of the rudder. Pressing the red master thumb button switch (msw) located on both yoke control wheels will disconnect the autopilot system; the yaw damper and all electric inputs to the aircraft trim control surfaces; except for the ailerons. Pressing the red msw button momentarily stops any further movement (runaway) of the trim surface(south) from electric input. This msw disconnect 'master switch' will not bring any of the trim positions back to neutral or center the tab position(south) while being pressed or after being released. So manual right rudder pedal input was required from both pilots; to compensate for the uncommanded left (yaw) rudder trim when the co-pilot attempted to correct the earlier yaw by using the rudder electric trim switch on the center control pedestal. At the same time; the captain was also pressing the msw switch on the control wheel and pulling the rudder (yaw) trim circuit breaker to disconnect the rudder electric trim motor and prevent any further movement of the trim tab. On descent; they did push the C/B for the rudder trim back in and were able to center the rudder trim yaw using the rudder trim controller switch that earlier appears to have caused the hard left yaw. They did re-pull the rudder trim control C/B afterwards to prevent any further uncommanded inputs. The reporter also reiterated the benefits of their recent recurrent simulator training in helping them deal with the uncommanded rudder trim input.

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Original NASA ASRS Text

Title: A LEAR-60 FLIGHT WAS INTERRUPTED BY A RUDDER TRIM MALFUNCTION AT CRUISE FLIGHT. EMERGENCY DECLARED. LANDED SAFELY. CREW AND PASSENGERS OK.

Narrative: WE WERE ON AN IFR FLT PLAN. OUR FLT WAS INTERRUPTED BY A RUDDER TRIM MALFUNCTION AT CRUISE FLT. ON THIS DAY THE FLT CREW MET THE DIRECTOR OF MAINT AT THE MAINT REPAIR SHOP LOCATED AT ZZZ. THE ACFT HAD BEEN IN MAINT TO REPAIR A FLOW CTL VALVE IN THE PRESSURIZATION SYS. ALSO; THE COPLT'S PANEL HAD BEEN REMOVED TO REPAIR A RELAY FOR THE R PFD. THE WORK HAD BEEN COMPLETED IN THE EARLY AFTERNOON HRS. AFTER A THOROUGH PREFLT OF THE ACFT EXTERIOR AND INTERIOR THE FLT CREW ACCEPTED THE ACFT AND THE RETURN OF ACFT LOGS WITH APPROPRIATE LOGBOOK ENTRIES. THE FLT DEPARTED WITH ONLY THE FLT CREW ON BOARD. THE ENTIRE FLT WENT WELL; WITHOUT INCIDENT AND WE HAD A SUCCESSFUL TEST FLT AT ALT OF ALL SYS THROUGH ALL PHASES OF FLT. THE ACFT ARRIVED AT ZZZ1. AT ZZZ1 WE PUT ON 200 GALS OF JET-A WHILE WAITING 1 HR FOR THE PAX WHICH WERE RETURNING FOR A PART 91 FLT. ON THE RETURN TRIP I WAS FLYING FROM THE R SEAT ON AN IFR FLT PLAN. ON DEP WE NOTICED; ONCE WE ACTIVATED THE AUTOPLT AT 2000 FT MSL; THERE WAS AN AMBER E ON THE R SIDE PFD. I DISENGAGED THE AUTOPLT AND ACKNOWLEDGED THE PITCH FAULT FROM THE AUTOPLT. I THEN HAND FLEW THE ACFT AND CALLED FOR THE ABNORMAL CHKS. WE PROCEEDED TO CONTINUE PAST 10000 FT AND THEN BEGAN TO TROUBLESHOOT DURING THE CRUISE CLB. AFTER REACHING A CRUISE ALT AT FL210 WE CONCLUDED ALL CHKLISTS. AFTER VERIFYING ALL TRIM INDICATIONS AND TRIM POS I REENGAGED THE AUTOPLT TO SEE IF THE ACFT HAD BEEN RE-TRIMMED PROPERLY. AFTER RE-ENGAGING WE GOT THE AMBER E ON THE COPLT MFD AND THE RED TRIM LIGHT ON THE AUTOPLT. WE DISCONNECTED AGAIN THEN TRIED DUPLICATING WITH AN AUTOPLT XFER TO THE PLT SIDE. THE PROB DID NOT DUPLICATE THIS TIME. WE CONTINUED TO HAND FLY AND I TOOK THE CTLS BACK AND FLEW FROM THE COPLT SIDE. WHILE ON A VECTOR TO THE ARR AND FLYING WITH THE AUTOPLT OFF I NOTICED THE PLANE WAS TRIMMED BUT WAS INDICATING A SLIGHTLY OUT OF TRIM YAW INDICATION. I PROCEEDED TO DISENGAGE THE YAW DAMPENER AND APPLY A VERY SLIGHT INPUT TO YAW THE NOSE SLIGHTLY R. UPON ENGAGING THE RUDDER TRIM CTL PANEL THE ACFT WENT TO 60% L TRIM; YAWING THE ACFT L; CAUSING ME TO IMMEDIATELY GO TO THE MSW (MASTER THUMB SWITCH) AND HOLD THE CTL SWITCH DOWN WHICH TEMPORARILY DISCONNECTED. THE CAPT THEN TOOK THE CTLS IN THE PLT SEAT AND WE ACKNOWLEDGED WE WERE COMPLETELY OUT OF TRIM. TO CONFIRM THE SITUATION THE CAPT MOMENTARILY RELEASED THE MSW SWITCH WHILE WE BOTH KEPT HVY PRESSURE ON THE R RUDDER PEDAL AND HIS L-HAND HELD THE YAW TRIM CIRCUIT BREAKER. HE CONFIRMED THE RUDDER CTL PANEL HAD BEEN IN THE CTR POS; BUT WHEN HE RELEASED THE MSW THE PLANE CONTINUED TO YAW FURTHER AND THEN HE REPRESSED THE MSW SWITCH AND SIMULTANEOUSLY PULLED THE YAW TRIM CIRCUIT BREAKER. WE HAD VERIFIED CTL OF THE ACFT AND DECLARED AN EMER ADVISING WE ARE PAN-PAN WITH RUDDER TRIM MALFUNCTION; HAVE REGAINED CTL AND NEEDED ALT DISCRETION AND VECTORS TO ZZZ2 DUE TO WX. WE SLOWED DOWN THE ACFT AND WENT THROUGH THE EMER CHKLIST. WE MANAGED TO ISOLATE ALL ISSUES TO THE RUDDER TRIM AND DECIDED TO FIX IN ORDER TO AVOID LNDG WITH AN ASYMMETRIC THRUST OR IN A SEVERE SLIP CONDITION. WHILE DSNDING WE PUSHED THE YAW TRIM BREAKER AND REAPPLIED THE RUDDER TRIM CTLR TO CTR THE YAW TRIM FORCES. THIS WORKED AND THEN WE DISENGAGED THE YAW TRIM BREAKER AND MONITORED ALL TRIM FUNCTIONS CLOSELY WHILE THE CAPT HAND FLEW THE ACFT. WE LANDED SAFELY AT ZZZ2 WITH ALL PAX AND CREW OK. I BELIEVE THE DETERMINING FACTOR THAT ALLOWED THIS FLT CREW TO RESPOND QUICKLY AND ACCURATELY CAME FROM GOOD SIMULATOR TRAINING AND GOOD CRM IN AN EMER SITUATION. THIS LED TO EFFICIENT TROUBLESHOOTING AND CORRECTIONS. THERE WAS COMPLETE AGREEMENT FROM BOTH CREW MEMBERS ON THE EMER SITUATION FOLLOWED BY THE CORRECTIVE ACTION. THIS IS AN INCREDIBLE LEARNING EXPERIENCE AND WE ALL HOPE TO NEVER HAVE TO DUPLICATE IN ACTUAL FLT CONDITIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT LEAR ACFT USES THE TERMINOLOGY 'YAW TRIM ' AND 'YAW TRIM CONTROLLER' INSTEAD OF 'RUDDER TRIM' OR 'RUDDER TRIM CTL.' THE TERMS ARE USED INTERCHANGEABLY IN THE TEXT OF HIS REPORT AND APPLY TO THE SAME SYSTEM; WHICH IS TRIM CONTROL OF THE RUDDER. THIS RUDDER SYSTEM HAS AN ELECTRIC CONTROLLED RUDDER TRIM TAB ON THE LOWER PART OF THE RUDDER. PRESSING THE RED MASTER THUMB BUTTON SWITCH (MSW) LOCATED ON BOTH YOKE CONTROL WHEELS WILL DISCONNECT THE AUTOPILOT SYSTEM; THE YAW DAMPER AND ALL ELECTRIC INPUTS TO THE ACFT TRIM CONTROL SURFACES; EXCEPT FOR THE AILERONS. PRESSING THE RED MSW BUTTON MOMENTARILY STOPS ANY FURTHER MOVEMENT (RUNAWAY) OF THE TRIM SURFACE(S) FROM ELECTRIC INPUT. THIS MSW DISCONNECT 'MASTER SWITCH' WILL NOT BRING ANY OF THE TRIM POSITIONS BACK TO NEUTRAL OR CENTER THE TAB POSITION(S) WHILE BEING PRESSED OR AFTER BEING RELEASED. SO MANUAL RIGHT RUDDER PEDAL INPUT WAS REQUIRED FROM BOTH PILOTS; TO COMPENSATE FOR THE UNCOMMANDED LEFT (YAW) RUDDER TRIM WHEN THE CO-PILOT ATTEMPTED TO CORRECT THE EARLIER YAW BY USING THE RUDDER ELECTRIC TRIM SWITCH ON THE CENTER CONTROL PEDESTAL. AT THE SAME TIME; THE CAPTAIN WAS ALSO PRESSING THE MSW SWITCH ON THE CONTROL WHEEL AND PULLING THE RUDDER (YAW) TRIM CIRCUIT BREAKER TO DISCONNECT THE RUDDER ELECTRIC TRIM MOTOR AND PREVENT ANY FURTHER MOVEMENT OF THE TRIM TAB. ON DESCENT; THEY DID PUSH THE C/B FOR THE RUDDER TRIM BACK IN AND WERE ABLE TO CENTER THE RUDDER TRIM YAW USING THE RUDDER TRIM CONTROLLER SWITCH THAT EARLIER APPEARS TO HAVE CAUSED THE HARD LEFT YAW. THEY DID RE-PULL THE RUDDER TRIM CONTROL C/B AFTERWARDS TO PREVENT ANY FURTHER UNCOMMANDED INPUTS. THE REPORTER ALSO REITERATED THE BENEFITS OF THEIR RECENT RECURRENT SIMULATOR TRAINING IN HELPING THEM DEAL WITH THE UNCOMMANDED RUDDER TRIM INPUT.

Data retrieved from NASA's ASRS site as of January 2009 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.