What was found
TO IDENTIFY THE SUSPECTED POPULATION, MTU-H REVIEWED ALL SHOP VISITS INVOLVING WORK SCOPES THAT REQUIRED REMOVAL AND REINSTALLATION OF IGV LEVER ARMS WITHOUT ACCESS TO THE IGVS. THE POPULATION WAS SUBSEQUENTLY NARROWED BY EXCLUDING ENGINES FOR WHICH THE FAN HUB FRAME (FHF) WAS EXPOSED AT MODULE LEVEL, SUCH AS DURING HPC MODULE REMOVAL, AS THE IGVS ARE VISIBLE AND CAN BE VISUALLY INSPECTED AFTER LEVER ARM INSTALLATION. IN ADDITION, ENGINES THAT UNDERWENT A SUBSEQUENT SHOP VISIT WITH THE FHF EXPOSED WERE ALSO EXCLUDED FROM THE SUSPECTED POPULATION. THE REMAINING ENGINES WERE THEREFORE CLASSIFIED AS POTENTIALLY AFFECTED. IT SHOULD BE NOTED THAT WORK SCOPES PROVIDING ACCESS TO THE IGVS INCLUDE SEVERAL QUALITY GATES DURING ASSEMBLY THAT ARE INTENDED TO IDENTIFY ANY LEVER ARM MISORIENTATION THROUGH VISUAL INSPECTION. FURTHERMORE, THE APPLICABLE TASK CARDS REQUIRE A VERIFICATION OF THE IGV POSITIONS FOLLOWING LEVER ARM INSTALLATION TO PREVENT INCORRECT ORIENTATION. THE IDENTIFIED POTENTIALLY AFFECTED CUSTOMERS AND RELEVANT AUTHORITIES WERE SUBSEQUENTLY INFORMED. ALL POTENTIALLY AFFECTED ENGINES IN SHOP WERE CHECKED PRIOR SHIPMENT. THE INTERNAL ASSEMBLY AND INSPECTION PROCEDURES WERE CHECKED AND REVISED TO IMPLEMENT AN ADDITIONAL BORESCOPE INSPECTION (BSI) AFTER ENGINE ASSEMBLY FOR ENGINES WITHOUT ACCESS TO THE IGVS TO DETERMINE THE CORRECT ORIENTATION OF ALL IGVS PRIOR TO ENGINE TESTING. A LESSONS LEARNED / QUALITY ALERT WAS DISTRIBUTED TO THE ENGINE AND MODULE ASSEMBLY SHOP STAFF TO RAISE AWARENESS ABOUT THIS TOPIC. FOR VARIABLE HPC STATOR VANES THIS CONDITION WOULD BE CLASSIFIED AS OFF-SCHEDULE VANE (VSV) OPERATION, AS OUTLINED IN ESM 72-00-00 INSPECTION 002, SUBTASK 72-00-00-220-089 WHILE THIS CONDITION FOR IGVS IS NOT DESCRIBED. ACCORDING TO THE REFERENCED SUBTASK, THE BLADES OF ONE STAGE FORWARD AND TWO STAGES AFT MUST BE SCRAPPED. PER RECENT OEM INQUIRIES IGV MISORIENTATION DOES NOT REQUIRE THE FORWARD (LPC STAGE) TO BE SCRAPPED (SEE ROOT CAUSE ANALYSIS). A REVIEW OF MAINTENANCE RECORDS INDICATED, THAT SIMILAR WORK WAS PERFORMED ON MULTIPLE ENGINES. ALL OF THESE ENGINES UNDERWENT MAINTENANCE ON THE FBC MODULE OR ENGINE/PROPULSOR. THIS WORKSCOPE INCLUDED THE REMOVAL OF IGV LEVER ARMS, ALLOWING THE IGVS TO MOVE FREELY AROUND THEIR INDIVIDUAL RADIAL AXES. CONSEQUENTLY, THE CHANGE IN ORIENTATION MAY GO UNDETECTED PRIOR TO THE REINSTALLATION OF THE LEVER ARM, POTENTIALLY LEADING TO MISALIGNMENT. THE ORIENTATION OF AN IGV LEVER ARM ON THE IGV TRUNNION CAN BE ROTATED BY 180° DURING INSTALLATION, BECAUSE THE SHAPE OF THE PARTS DOES NOT PREVENT THIS SUFFICIENTLY. BASED ON THE MAINTENANCE RECORDS, IT CANNOT BE RULED OUT, THAT INDIVIDUAL IGVS REMAINED IN INCORRECTLY INSTALLED POSITION IN THE POTENTIALLY AFFECTED ENGINE POPULATION WITHOUT BEING NOTICED. MTU-H HAS REACHED OUT TO THE ORIGINAL EQUIPMENT MANUFACTURER (OEM) FOR TECHNICAL SUPPORT. THE OEM RECOMMENDED TO INSPECT POTENTIALLY AFFECTED ENGINES OF INCORRECT INSTALLED IGVS. MISORIENTED IGVS CREATE ABNORMAL PERTURBATION INTO THE FLOW PATH. IT IS THE RECOMMENDATION TO GO BACK TO THE APPROVED CONFIGURATION AS SOON AS THE ISSUE IS DETECTED. THE OPERATION OF THE ENGINE CANNOT BE CONTINUED UNTIL THE NEXT SHOP VISIT AND NO DR OR CONTINUE IN SERVICE LIMIT CAN BE GRANTED IF IGV MISORIENTATION IS EVIDENCED. OFF SCHEDULE VSV OPERATION IS DESCRIBED IN EM 72-00-00 INSPECTION 002, SUBTASK 72-00-00-220-089. ACCORDING TO THIS SUBTASK, THE LPC STAGE 5, HPC BLISK STAGE 1, AND HPC BLADES STAGE 2 SHALL BE REPLACED BEFORE ANY FURTHER OPERATION CAN TAKE PLACE. THIS SUBTASK DOES NOT CLEARLY PROVIDE INSTRUCTIONS FOR THOSE IGV OFF-SCHEDULE OPERATION. AS PART OF THE OEM RECOMMENDATION MTU HAS RECEIVED INSTRUCTIONS FOR PART DISPOSITION IN CASE INCORRECTLY INSTALLED IGVS ARE DETECTED. THIS INCLUDES THAT ONLY THE HPC BLISK STAGE 1 AND HPC BLADES STAGE 2, AS WELL AS THE IMPACTED IGVS WITH LEVER ARMS AND ASSOCIATED HARDWARE, ALONG WITH BOTH ADJACENT IGVS (RIGHT AND LEFT) OF THE REVERSED IGV WITH LEVER ARMS AND ASSOCIATED HARDWARE, MUST BE DISCARDED REGARDLESS OF THEIR VISUAL CONDITION.
ROOT CAUSE ANALYSIS: A ROOT CAUSE ANALYSIS WAS CONDUCTED BY MTU-H TO IDENTIFY THE PRIMARY CONTRIBUTORS TO THE CURRENT EVENT. THE ANALYSIS WAS PERFORMED USING AN ISHIKAWA DIAGRAM WHICH IDENTIFIED CONTRIBUTING FACTORS RELATED TO HUMAN FACTORS, MAINTENANCE PROCESSES, AND MATERIAL/DESIGN CHARACTERISTICS. MTU WORKPLANNING DEPARTMENT TRANSFERS THE OEM MANUAL REQUIREMENTS INTO INTERNAL WORKING DOCUMENTS (MASTERCARD) TO SUPPORT THE MECHANIC WITH BOTH, OEM INSTRUCTIONS BUT ALSO PROVIDE MTU EXPERIENCE AND EXPERTISE WHEN PERFORMING THE WORK. THIS IS DESCRIBED IN OPH-04-05-07-04. THIS INTERNAL PROCEDURE REQUIRES THE WORK PLANNER TO REFERENCE ALL TECHNICAL DATA USED IN THE DOCUMENT TO ENSURE APPROPRIATE INCORPORATION OF CHANGES. THE MASTERCARD FOR FAN HUB FRAME MODULE WAS COMPILED BASED ON OEM TASK TASK 72-23-00-040-001 (DISASSEMBLY) AND 72-23-00-440-001 (ASSEMBLY). THE TASKS WERE USED FOR BOTH, FBC AND FHF WORKSCOPES. IN 2016 THE SPECIAL PROCEDURE 014 WAS ISSUED, WHICH AT THAT POINT OF TIME CONTAINED THE SAME REQUIREMENTS AS THE EM TASK AND THEREFORE THE WORK PLANNER DID NOT SEE A NEED TO REFERENCE THE SPECIAL PROCEDURE IN THE WORK PLAN. IN 2022 THE OEM REVISED THE SPECIAL PROCEDURE 014. AS THERE WAS NO REFERENCE TO THE SPECIAL PROCEDURE IN THE EXISTING MASTERCARD, THE CHANGE WAS NOT PROPERLY DETECTED AND IT WAS INADVERTENTLY MISSED TO IMPLEMENT THE REVISED REQUIREMENTS FROM THE SPECIAL PROCEDURE INTO THE MASTERCARD. A CHANGE OF THE WORK PLAN WOULD HAVE INITIATED ADDITIONAL GATES AS A FOUR EYE CHECK AND A FIRST ARTICLE/FIRST BUILD PROCESS TO ENSURE PROPER IMPLEMENTATION OF THE OEM REQUIREMENTS. DUE TO THE MISSING REFERENCE TO SPECIAL PROCEDURE 014 NO CHANGE WAS MADE TO MTU MASTERCARD AND THE ERROR REMAINED UNDETECTED. ESM 72-00-00 SPECIAL PROCEDURE 014 (IGV/VSV ACTUATING RINGS GUIDE PADS REPLACEMENT ON ENGINE OR PROPULSOR AT HORIZONTAL POSITION) WAS NOT YET INCLUDED IN THE MAINTENANCE PLANNING THUS HAVING NO INSTRUCTIONS IN THE TASK CARD. THIS WOULD HAVE INCLUDED A BORESCOPE INSPECTION OF ALL IGVS AFTER LEVER ARM INSTALLATION TO ENSURE CORRECT INSTALLATION. AT FAN BOOSTER COMPRESSOR (FBC) LEVEL, THE REQUIRED VISUAL INSPECTION (AS DEFINED IN THE APPLICABLE TASK CARD) COULD NOT BE PERFORMED AS DESCRIBED DUE TO ACCESSIBILITY LIMITATIONS. THE USED TASK CARD WAS VALID FOR WORK AT FAN HUB FRAME MODULE LEVEL. THE TASK CARD WAS APPLIED AT FBC LEVEL EVEN THOUGH ITS INSPECTION REQUIREMENTS COULD NOT BE FULLY ACCOMPLISHED AT THIS STAGE DUE TO ACCESSIBILITY LIMITATIONS. IN ADDITION, THE TRUNNION DESIGN INCORPORATES A SLIGHTLY CONICAL GEOMETRY FROM LEFT TO RIGHT. TRYOUTS SHOWED THAT NEVERTHELESS THE LEVER ARMS CAN BE MATED IN SEVERAL CASES TO THE TRUNNIONS IN WRONG DIRECTION LEADING TO THE DESCRIBED MISORIENTATION. THIS CONDITION CANNOT BE SEEN FROM EXTERNALLY. EXTERNAL IDENTIFICATION WOULD BE POSSIBLE BY ACCORDING WITNESS MARKS ON THE LEVER ARMS AS WELL AS THE IGV TRUNNION/STUD. THIS IS ONLY PARTIALLY CONSIDERED IN THE GE90-100 ESM AS THERE IS NO INSTRUCTION TO APPLY THESE MARKS. A MATERIAL REVIEW SHOWED THAT NEITHER NEW NOR USED PARTS HAVE THESE MARKS. THIS HAS BEEN REPORTED BACK TO THE OEM IN 2024 WHO PLANNED AN UPDATED TO THE ESM IN ORDER TO RECOMMEND TO PUT THIS MARK DURING 72-23-00 FAN HUB FRAME ASSEMBLY. THIS UPDATE IS NOT PUBLISHED TO DATE. AS A PRECAUTION, MTU-H USES A THREAD PROTECTION BUSHING SCREWED ON EACH INDIVIDUAL IGV STUD TO PREVENT DAMAGES TO THE THREADS. THIS BUSHING ALSO IMPEDES FREE MOVEMENT WHEN THE IGV REMAINS INSTALLED IN THE FHF. ALL WORK PLANNERS WERE INFORMED ABOUT THIS ISSUE TO REMIND THEM OF THE IMPORTANCE OF SPECIAL PROCEDURES AND THEIR INCORPORATION INTO THE MASTERCARDS. THE INTERNAL PROCEDURE WILL BE REVIEWED AND IMPROVED ACCORDINGLY TO PROVIDE IMPROVED INSTRUCTION ON REFLECTING THE REFERENCES OF INCORPORATED DOCUMENTS SUCH AS SPECIAL PROCEDURES. ALL SPECIAL PROCEDURES WILL BE REVIEWED FOR CORRECT IMPLEMENTATION. MTU-H HAS REVISED THE MASTERCARD AND IMPLEMENTED A MANDATORY 360-DEGREE BORESCOPE INSPECTION (BSI) OF THE IGVS FOLLOWING LEVER ARM REINSTALLATION IN ACCORDANCE WITH GE90-100 ESM 72-00-00 SPECIAL PROCEDURES 014, SUBTASK 72-00-00-220-384 AS A STANDARD PROCEDURE FOR FUTURE ENGINES UNDERGOING THE APPLICABLE WORK SCOPE.