Narrative:

Flight control system malfunction (pitch trim) while at FL290 from an initial descent from our cruising altitude of FL330, we were alerted that the autoplt, while engaged, switched from the left automatic flight control system (left afcs) to the right afcs. Although there is no specific procedure in the abnormal procedures checklist for this failure, with our own troubleshooting ideas, we selected the autoplt back to the left afcs to see if we would get a repeat of the failure. Shortly thereafter, the autoplt switched back to the right afcs leaving the left afcs fail annunciator illuminated and the autoplt disengaged itself. It was at this point when the PF observed the elevator trim had been commanded by the autoplt to the full nose down position. The crew then realized the autoplt failures and disconnection was a result of the autoplt not being able to command enough nose down trim. A fair amount of forward pressure was needed on the control yoke to keep level flight while the elevator trim was at the nose down hard-stop position. This was verified while taking turns flying the aircraft and discussing what we observed. At this point, the only way to keep level flight was to pull the power back. The PF had the aircraft stabilized at FL290 with an airspeed of approximately 260-270 KIAS from 300 KIAS. Here, there was approximately 1 inch of nose down pitch trim according to the white band on the trim wheel. The PIC then contacted our maintenance operations where it was agreed to divert to ZZZ. At this point, our time to the destination and the time to our diversion airport were about equal (approximately 45 mins). Just before our descent to ZZZ, the PIC went to the back to move our crew bags from the rear cargo bay to the front cargo bay in order to move the center of gravity forward, which would increase controllability should we experience this situation again. Sure enough, while he was back there, the PF noticed the autoplt slowly moving the pitch trim down while at 270 KIAS. Just before he had accomplished moving the bags, the pitch wheel was just at its forward limit again. The rest of the flight was uneventful during descent and landing. It should also be stated there were 2 other write-ups in the previous 2 weeks, concerning similar occurrences. The corrective action of both occurrences was the re-rigging of the flight control system. The PIC notified the appropriate company officials of this situation the day of the incident and the following day so as to direct the company to what the flight crew believed was a reportable notification, to adhere to the NTSB part 830 regulations. Both the company FAA chief inspector and the company fleet program manager, relayed to the PIC that they determined the problem experienced was in fact not a flight control system malfunction or failure. Both the PIC and sic were instructed to fill out an incident report form. Callback conversation with reporter revealed the following information: reporter alleges that he felt pressured by the company and the inspector to amend his characterization of the anomaly. Although, as a new employee, the reporter felt the flight crew had done nothing wrong. In fact, he felt they performed in a professional manner in response to an aircraft malfunction. He also stated the company maintenance personnel were very professional and would not allow themselves to be pressured into an incomplete examination and repair resolution. They scheduled the aircraft for a day and a half of maintenance activity. At this point the reporter is unsure about the disposition of the aircraft.

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Original NASA ASRS Text

Title: FLT CREW OF H25B ENCOUNTERED MALFUNCTIONING PITCH CTL MECHANISMS IN CRUISE. EVEN WITH FULL NOSE DOWN PITCH TRIM, FORWARD ELEVATOR PRESSURE WAS REQUIRED TO MAINTAIN LEVEL FLT.

Narrative: FLT CTL SYS MALFUNCTION (PITCH TRIM) WHILE AT FL290 FROM AN INITIAL DSCNT FROM OUR CRUISING ALT OF FL330, WE WERE ALERTED THAT THE AUTOPLT, WHILE ENGAGED, SWITCHED FROM THE L AUTOMATIC FLT CTL SYS (L AFCS) TO THE R AFCS. ALTHOUGH THERE IS NO SPECIFIC PROC IN THE ABNORMAL PROCS CHKLIST FOR THIS FAILURE, WITH OUR OWN TROUBLESHOOTING IDEAS, WE SELECTED THE AUTOPLT BACK TO THE L AFCS TO SEE IF WE WOULD GET A REPEAT OF THE FAILURE. SHORTLY THEREAFTER, THE AUTOPLT SWITCHED BACK TO THE R AFCS LEAVING THE L AFCS FAIL ANNUNCIATOR ILLUMINATED AND THE AUTOPLT DISENGAGED ITSELF. IT WAS AT THIS POINT WHEN THE PF OBSERVED THE ELEVATOR TRIM HAD BEEN COMMANDED BY THE AUTOPLT TO THE FULL NOSE DOWN POS. THE CREW THEN REALIZED THE AUTOPLT FAILURES AND DISCONNECTION WAS A RESULT OF THE AUTOPLT NOT BEING ABLE TO COMMAND ENOUGH NOSE DOWN TRIM. A FAIR AMOUNT OF FORWARD PRESSURE WAS NEEDED ON THE CTL YOKE TO KEEP LEVEL FLT WHILE THE ELEVATOR TRIM WAS AT THE NOSE DOWN HARD-STOP POS. THIS WAS VERIFIED WHILE TAKING TURNS FLYING THE ACFT AND DISCUSSING WHAT WE OBSERVED. AT THIS POINT, THE ONLY WAY TO KEEP LEVEL FLT WAS TO PULL THE PWR BACK. THE PF HAD THE ACFT STABILIZED AT FL290 WITH AN AIRSPD OF APPROX 260-270 KIAS FROM 300 KIAS. HERE, THERE WAS APPROX 1 INCH OF NOSE DOWN PITCH TRIM ACCORDING TO THE WHITE BAND ON THE TRIM WHEEL. THE PIC THEN CONTACTED OUR MAINT OPS WHERE IT WAS AGREED TO DIVERT TO ZZZ. AT THIS POINT, OUR TIME TO THE DEST AND THE TIME TO OUR DIVERSION ARPT WERE ABOUT EQUAL (APPROX 45 MINS). JUST BEFORE OUR DSCNT TO ZZZ, THE PIC WENT TO THE BACK TO MOVE OUR CREW BAGS FROM THE REAR CARGO BAY TO THE FRONT CARGO BAY IN ORDER TO MOVE THE CTR OF GRAVITY FORWARD, WHICH WOULD INCREASE CONTROLLABILITY SHOULD WE EXPERIENCE THIS SIT AGAIN. SURE ENOUGH, WHILE HE WAS BACK THERE, THE PF NOTICED THE AUTOPLT SLOWLY MOVING THE PITCH TRIM DOWN WHILE AT 270 KIAS. JUST BEFORE HE HAD ACCOMPLISHED MOVING THE BAGS, THE PITCH WHEEL WAS JUST AT ITS FORWARD LIMIT AGAIN. THE REST OF THE FLT WAS UNEVENTFUL DURING DSCNT AND LNDG. IT SHOULD ALSO BE STATED THERE WERE 2 OTHER WRITE-UPS IN THE PREVIOUS 2 WKS, CONCERNING SIMILAR OCCURRENCES. THE CORRECTIVE ACTION OF BOTH OCCURRENCES WAS THE RE-RIGGING OF THE FLT CTL SYS. THE PIC NOTIFIED THE APPROPRIATE COMPANY OFFICIALS OF THIS SIT THE DAY OF THE INCIDENT AND THE FOLLOWING DAY SO AS TO DIRECT THE COMPANY TO WHAT THE FLT CREW BELIEVED WAS A REPORTABLE NOTIFICATION, TO ADHERE TO THE NTSB PART 830 REGS. BOTH THE COMPANY FAA CHIEF INSPECTOR AND THE COMPANY FLEET PROGRAM MGR, RELAYED TO THE PIC THAT THEY DETERMINED THE PROB EXPERIENCED WAS IN FACT NOT A FLT CTL SYS MALFUNCTION OR FAILURE. BOTH THE PIC AND SIC WERE INSTRUCTED TO FILL OUT AN INCIDENT RPT FORM. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ALLEGES THAT HE FELT PRESSURED BY THE COMPANY AND THE INSPECTOR TO AMEND HIS CHARACTERIZATION OF THE ANOMALY. ALTHOUGH, AS A NEW EMPLOYEE, THE RPTR FELT THE FLT CREW HAD DONE NOTHING WRONG. IN FACT, HE FELT THEY PERFORMED IN A PROFESSIONAL MANNER IN RESPONSE TO AN ACFT MALFUNCTION. HE ALSO STATED THE COMPANY MAINT PERSONNEL WERE VERY PROFESSIONAL AND WOULD NOT ALLOW THEMSELVES TO BE PRESSURED INTO AN INCOMPLETE EXAMINATION AND REPAIR RESOLUTION. THEY SCHEDULED THE ACFT FOR A DAY AND A HALF OF MAINT ACTIVITY. AT THIS POINT THE RPTR IS UNSURE ABOUT THE DISPOSITION OF THE ACFT.

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.