A B757-200 WAS DISPATCHED IN NON COMPLIANCE WITH A FIRST STAGE TURBINE BLADE CRACKED BEYOND MAINT MANUAL ALLOWABLE LIMITS.

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I AM A B757 MAINT COORDINATOR WITH ACR COMPANY IN ZZZ. ON MAY/MON/02 I WAS ON DUTY XA00-XI00) AND RECEIVED A CALL FROM A MEMBER OF OUR ZZZ1 INSPECTION TEAM. HE HAD JUST COMPLETED A ROUTINE HOT- SECTION BOROSCOPE OP ON THE L ENG ON SHIP X; AND CALLED TO RPT FINDING A CRACK ON A FIRST STAGE TURBINE BLADE. PER THE INFO FROM ZZZ1; THE CRACK HAD 2 LEGS WITH LENGTHS OF .171 INCH BY .125 INCH; AND PER THE ZZZ1 INSPECTOR; THIS FELL WITHIN MAINT MANUAL 72-00-00-6 LIMITS FOR CONTINUED IN-SVC OP BUT RESTRICTS THE ENG TO 10 FLT CYCLES BEFORE REPLACEMENT. ZZZ1 ENTERED THE LOG SHEET FOR HAVING COMPLETED THE BOROSCOPE OP AND ASKED ME TO ENTER WHAT IS KNOWN AS A DEFERRED ITEM INTO THE OUTSTANDING MAINT ITEM COMPUTER RECORDS FOR SHIP X. (THIS IS A COMMON FUNCTION OF A MAINT COORDINATOR.) THE DEFERRED ITEM THAT I ENTERED STATED THE FINDINGS OF THE BOROSCOPE ON THE #1 ENG; RESTR THE ENG OP TO 10 CYCLES AND DIRECTED ROUTING OF THE AIRPLANE TO ZZZ FOR A #1 ENG CHANGE. I DID COMPLETE THE DEFERRED ITEM INSTALLATION INTO THE ACFT RECORDS; BUT I NEGLECTED TO CHK THE MAINT MANUAL REF THAT NIGHT. AS IT TURNS OUT; IT IS NOT VALID FOR THIS PARTICULAR CRACK. THE MAINT MANUAL 72-00-00-6 LIMIT FOR A 10 CYCLE RESTR IS .150 INCH BY .150 INCH; SO 1 LEG OF THIS CRACK WAS .021 INCH OUT OF MAINT MANUAL LIMITS. THE AIRPLANE MADE 5 FLTS BEFORE THE B757 COORDINATOR ON DUTY ON MAY/WED/02 NOTICED THE DISCREPANCY AND REMOVED THE ACFT FROM REVENUE SVC IN ZZZ3; FL. THE AIRPLANE WAS SUBSEQUENTLY MAINT FERRIED TO ZZZ FOR AN ENG CHANGE. A FOLLOW-UP BOROSCOPE REVEALED THAT THE CRACK HAD NOT PROPAGATED. I WAS MADE AWARE OF MY OVERSIGHT WHEN I RPTED FOR DUTY ON MAY/WED/02. THE MAIN REASON FOR THIS EVENT IS THAT I WAS LAX IN MY DUTIES TO CONFIRM THE MAINT MANUAL REF WAS INDEED APPLICABLE TO THE CRACK IN QUESTION. I ASSUMED THAT THE INSPECTOR HAD 'DEALT WITH ENOUGH HOT SECTION CRACKS THAT HE HAD THIS MAINT MANUAL REF MEMORIZED.' THIS WAS A FAILURE ON MY PART.