A DHC8-400 #2 ENG INTER COMPRESSOR CASE BORESCOPE INSPECTION FOUND A CRACK. INSPECTOR RPTED CRACK BUT FAILED TO INITIATE A TIME DEFERRAL FOR 65 HR INSPECTION INTERVAL PER ENGINEERING ORDER.

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ACFT WAS THE LATE ROUTINE OVERNIGHT CHK AND WAS SCHEDULED 21.3 PRODUCTION HRS ON THE ACFT. THE AFT ARRIVED AT XA55 WAS DUE OUT AT XF00. AVAILABLE MAINT TIME WAS APPROX 4 HRS (1/2 HRS TO LET PAX OFF AND 1/2 TO BE CLR OF THE ACFT IN THE MORNING). ZZZ HAD 4 ROUTINE OVERNIGHT CHKS FOR THE NIGHT. STAFFING INCLUDED 4 MECHS AND 1 LEAD MECH. A 200 HR INTER COMPRESSOR CASE BORESCOPE INSPECTION WAS SCHEDULED FOR THE #2 ENG. #1 ENG WAS EXEMPT DUE TO BEING POST SVC BULLETIN 35152. THE LEVEL 2 BORESCOPE QUALIFIED MECH DETERMINED THAT THERE WAS A CRACK IN THE 'LIP' AT THE 3 O'CLOCK POS. ACFT RECORDS HAS NO RECORD THAT A TIME DEFERRED ITEM WAS GENERATED TO DOWNGRADE AND TRACK THE ENG AT A NEW 65 HR INTERVAL. SPOKANE DID NOT RPT A TIME DEFERRED ITEM GENERATION FOR THE #2 ENG ON THE ZZZ ACTIVITY RPT. NO NON ROUTINE TALLEY WAS RECEIVED IN ZZZ1 INDICATING A TIME DEFERRED ITEM WAS GENERATED. A REVIEW OF THE RECORDS INDICATES THAT THE ENGINEERING ORDER WAS REISSUED TO ZZZ1 FOR THE SAME SERIAL NUMBER ENG ON APR/XA/06. THE BORESCOPE MECH AT THAT TIME DETERMINED THAT THERE WERE 'NO CRACKS' FOUND. MAY/XA/06; I WAS INFORMED THAT ACR X WAS BEING STOPPED IN ZZZ3 TO PERFORM A BORESCOPE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THERE WAS NO MRSI INITIATED BY THE STATION ON THE INTER COMPRESSOR CASE CRACK. THE MRSI IS A TIME DEFERRED ITEM AUTHORIZED BY ENGINEERING ORDER TO ALLOW INSPECTIONS TO BE PERFORMED AT GREATER THAN 65 HR INTERVALS. THIS INTER COMPRESSOR CASE CRACK COULD HAVE SLIPPED THROUGH THE CRACKS AND NEVER BE VISIBLE WITHOUT THE MRSI. FORTUNATELY THE TECHNICIAN ACCOMPLISHING THE BORESCOPE DID RPT THE FINDINGS AND CLR THE CALLOUT THAT FORCED THE INSPECTION.