Narrative:

Aircraft X diverted to ZZZZ from ZZZZ1 while en route to ZZZ on xx/xx/19 for unsched stabilizer trim EICAS (engine indication and crew alerting system) caution and aural warning; accompanied by unsched stabilizer trim overhead indication. EICAS caution came on intermittently within minutes of taxing out in ZZZZ1. We proceeded to a remote parking area; established contact with dispatch/[maintenance control] and complied with [maintenance control] procedure involving pulling 4 cbs (circuit breakers); moving yoke trim and alternate trim actuators; stab trim cutout switches and observing full rate and half rate movement. Cautions cleared; but we cautiously elected with [maintenance control] concurrence to gate return for ZZZZ1 maintenance to review possible faults with stabilizer trim/aileron lockout modules (sams) and stabilizer trim control modules (stcms). This cautious decision to gate return in ZZZZ1 was based upon our identical circumstance leaving ZZZ [aircraft Y; another B767] xx/xy/19 with same aircraft and scenario during taxi prior to departure and [maintenance control] contact and subsequent clearing of caution. When we had the identical circumstance in ZZZ and subsequent to extensive ground delays due to weather; we were confident the maintenance issue was resolved. After ZZZZ1 gate return; maintenance advised of system reset; they were nuisance faults which cleared and we were okay to continue. With new mrd (maintenance release document); we took off for ZZZ; passing approximately FL120 (12;000 ft.) with autopilot engaged; received intermittent EICAS message - unsched stabilizer trim caution and aural warning; accompanied by unsched stabilizer trim overhead light indication. We disengaged autopilot and reviewed 767 QRH (quick reference handbook) noting no actual trim movement was observed. We did not continue the QRH below the conditional statement - 'condition: stabilizer movement occurs without a signal to trim'. We contacted dispatch and [maintenance control] via satcom (satellite communications) to discuss EICAS caution and possible diversion options. Coordination with [maintenance control] indicated the repair would be more efficiently completed in ZZZZ; closer to parts from [company] ZZZZ2 maintenance. Dispatch was advised and the op's manager wanted us to return to ZZZZ1; we queried this decision based upon our geographic position (over the english channel); availability of maintenance and parts; along with the fact we did not have any passengers; at which point the operations manager agreed with [maintenance control] and our decision to divert to ZZZZ. We did not declare an emergency or request priority handling and performed a normal landing in ZZZZ. There were no passengers on board; crew members consisted of 7 flight attendants and 3 pilots. We also were loaded with 8 pallets of revenue cargo. The next day; after extensive delays; we attempted to fly ZZZ [aircraft Z; another B767] ZZZZ - ZZZ; however; unsched stabilizer trim EICAS caution message popped up intermittently after clearing EICAS messages during before push checklist; with no aural tone; which is inhibited while parked on the ground. All instances of these EICAS events; the caution was intermittent; but persistent with 12+ repeat intermittent cautions in ZZZ prior to the [maintenance control] procedure resolving the issue; 8+ in ZZZZ1; prior to gate return; none subsequent to gate return until airborne; during climb out then 12+ en route to ZZZZ and finally 10+ in ZZZZ when preparing to push. Station operations personnel observed several of the intermittent cautions and british airways mechanic indicated we had the same latched faults with both sams and left stcms after they have been replaced; indicating additional troubleshooting would be required.aircraft Y - xx/xx/19 - taxi out intermittent unsched stabilizer trim; [maintenance control] procedure clears.aircraft X - xx/xy/19 - taxi out intermittent unsched stabilizer trim; [maintenance control] procedure clears.aircraft X - xx/xy/19 - gate return; ZZZZ1 maintenance clears all faults; indicates we are ok to go.aircraft X - xx/xy/19 - takeoff; during climb intermittent unsched stabilizer trim; divert to ZZZZ.aircraft Z - xx/xz/19 - before taxi checklist intermittent unsched stabilizer trim; cancel.aircraft Z - xx/xa/19 - scheduled to operate; maintenance still working on aircraft.

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Original NASA ASRS Text

Title: B767 flight crew reported multiple aircraft encountered multiple Stabilizer Trim anomalies.

Narrative: Aircraft X diverted to ZZZZ from ZZZZ1 while en route to ZZZ on XX/XX/19 for UNSCHED STAB TRIM EICAS (Engine Indication and Crew Alerting System) caution and aural warning; accompanied by UNSCHED STAB TRIM overhead indication. EICAS caution came on intermittently within minutes of taxing out in ZZZZ1. We proceeded to a remote parking area; established contact with Dispatch/[Maintenance Control] and complied with [Maintenance Control] procedure involving pulling 4 CBs (Circuit Breakers); moving yoke trim and alternate trim actuators; stab trim cutout switches and observing full rate and half rate movement. Cautions cleared; but we cautiously elected with [Maintenance Control] concurrence to gate return for ZZZZ1 Maintenance to review possible faults with Stabilizer Trim/Aileron Lockout Modules (SAMs) and Stabilizer Trim Control Modules (STCMs). This cautious decision to gate return in ZZZZ1 was based upon our identical circumstance leaving ZZZ [Aircraft Y; another B767] XX/XY/19 with same aircraft and scenario during taxi prior to departure and [Maintenance Control] contact and subsequent clearing of caution. When we had the identical circumstance in ZZZ and subsequent to extensive ground delays due to weather; we were confident the maintenance issue was resolved. After ZZZZ1 gate return; Maintenance advised of system reset; they were nuisance faults which cleared and we were okay to continue. With new MRD (Maintenance Release Document); we took off for ZZZ; passing approximately FL120 (12;000 ft.) with autopilot engaged; received intermittent EICAS message - UNSCHED STAB TRIM caution and aural warning; accompanied by UNSCHED STAB TRIM overhead light indication. We disengaged autopilot and reviewed 767 QRH (Quick Reference Handbook) noting no actual trim movement was observed. We did not continue the QRH below the conditional statement - 'Condition: Stabilizer movement occurs without a signal to trim'. We contacted Dispatch and [Maintenance Control] via SATCOM (Satellite Communications) to discuss EICAS caution and possible diversion options. Coordination with [Maintenance Control] indicated the repair would be more efficiently completed in ZZZZ; closer to parts from [Company] ZZZZ2 Maintenance. Dispatch was advised and the Op's Manager wanted us to return to ZZZZ1; we queried this decision based upon our geographic position (Over the English Channel); availability of maintenance and parts; along with the fact we did not have any passengers; at which point the Operations Manager agreed with [Maintenance Control] and our decision to divert to ZZZZ. We did not declare an emergency or request priority handling and performed a normal landing in ZZZZ. There were no passengers on board; crew members consisted of 7 Flight Attendants and 3 Pilots. We also were loaded with 8 pallets of revenue cargo. The next day; after extensive delays; we attempted to fly ZZZ [Aircraft Z; another B767] ZZZZ - ZZZ; however; UNSCHED STAB TRIM EICAS caution message popped up intermittently after clearing EICAS messages during Before Push Checklist; with no aural tone; which is inhibited while parked on the ground. All instances of these EICAS events; the caution was intermittent; but persistent with 12+ repeat intermittent cautions in ZZZ prior to the [Maintenance Control] procedure resolving the issue; 8+ in ZZZZ1; prior to gate return; none subsequent to gate return until airborne; during climb out then 12+ en route to ZZZZ and finally 10+ in ZZZZ when preparing to push. Station Operations personnel observed several of the intermittent cautions and British Airways Mechanic indicated we had the same latched faults with both SAMs and left STCMs after they have been replaced; indicating additional troubleshooting would be required.Aircraft Y - XX/XX/19 - Taxi out intermittent UNSCHED STAB TRIM; [Maintenance Control] procedure clears.Aircraft X - XX/XY/19 - Taxi out intermittent UNSCHED STAB TRIM; [Maintenance Control] procedure clears.Aircraft X - XX/XY/19 - Gate Return; ZZZZ1 maintenance clears all faults; indicates we are ok to go.Aircraft X - XX/XY/19 - Takeoff; during climb intermittent UNSCHED STAB TRIM; Divert to ZZZZ.Aircraft Z - XX/XZ/19 - Before Taxi Checklist intermittent UNSCHED STAB TRIM; Cancel.Aircraft Z - XX/XA/19 - Scheduled to operate; Maintenance still working on aircraft.

Data retrieved from NASA's ASRS site 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.