Air carrier technician reported that while reviewing the aircraft logbook of a B787 they found a carry forward item with incorrect limits applied to a high-pressure stage one turbine blade that had damage which caused an unscheduled engine change.

Narrative

Aircraft X out of service (OOS) in ZZZZ for High Vibs; metal in tailpipe and a GE Alert Notice issued (trends increasing); Engine No.2. Borescope revealed a broken/liberated High Pressure Turbine Stage 1 blade; fractured approx 30-40% up from blade root. While reviewing the aircraft Log Book; found an active carry forward defect for a Leading Edge crack in a High Pressure Turbine (HPT) Stage 1 blade; LP XXXXXXX with a limit of 250cycles. The Log Page text (work done) states the crack runs from blade cooling Holes row 3 through to row 9; Aircraft Maintenance Manual (AMM) stated is XX; Table X. Per this AMM if a crack extends past Row 8; Repeat inspections must be carried out every 50cycs or the engine must be changed before 25cycles or 10cycles (depending on SB status). This defect was raised at 2435cyc and a HPT stage 1 blade failed at 2650 cycles. The incorrect limits were applied to a damaged High Pressure Turbine Stage 1 Blade.The Defect and Manual was misinterpreted by all departments. The correct limits should have been applied to the Carry Forward by the Technician at the beginning. However Maintenance Control reviews and approves all defects and should have realized the error in the Limits trying to be applied. Similarly Quality Control (QC) also reviews defects (especially Borescope assessments) who again could have realized the error. Applying the the correct limits would have prevented an OOS and an engine change at a non company maintenance hub.