A DEHAVILLAND DHC-8-400 MECHANIC REPORTS ON THE PROBLEM WITH THE JOB CARDS AND THE PW150A ENG PROP BLADES' NICKEL SHEATH LEADING EDGE CONTINUING DELAMINATIONS; EVEN AFTER BLADE OVERHAUL.

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BLADE #6 ON THE #2 PROP OF ACFT HAD ENGINEERING ORDER SENT DOWN TO PERFORM 100 HR REINSPECTION TAP TEST. THIS BLADE IS POST SVC BULLETIN XX; DUE TO THE PART NUMBER; ONLY KNOWING ABOUT THIS AND SEEING THE LOW TIME AND 'ETCHING MARKS IN THE NICKEL SHEATH LEADING EDGE' DID I REALIZE THAT THIS TASK CARD WAS NOT APPLICABLE. I NA'ED THE ENTIRE TASK CARD; AND WAS NOT ALLOWED TO FOLLOW THE PROCS ON THIS CARD FOR BLADE CHANGE PROCS; WHICH IS TO ATTACH ENGINEERING ORDER. I DID ANSWER THE SURVEY QUESTIONS AS PER THE TASK CARD AND WROTE A NOTE STATING SIMILAR INFO. BLADE WAS REMOVED FROM ACFT DUE TO BEING OUT OF LIMITS PER THE DOWTY CMM REPAIR MANUAL. FIX THIS MAJOR PROB WITH THIS SERIES TASK CARDS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THESE ARE COMPOSITE TYPE DOWTY PROP BLADES UTILIZING ONLY AN EIGHT THOUSANDTH (.008) THICK; COMPOUND CURVED; NICKEL SHEATH LEADING EDGE CAP (GUARD); THAT IS BONDED TO THE PROP BLADE. THE PROP MANUFACTURER; DOWTY; HAS A SERVICE BULLETIN THAT ALLOWS SOME DELAM OF THE NICKEL SHEATH AREA TO BE REPAIRED USING A SPECIAL ADHESIVE. THIS DELAM PROBLEM WAS THE RESULT OF THE MANUFACTURING PROCESS OF THE NICKEL SHEATH MATERIAL THAT LEFT SMALL ETCH LINES OR HOLES IN THE SHEATH GUARD. THESE GUARDS WERE THEN BONDED TO THE PROP BLADE. WATER AND MOISTURE ULTIMATELY ENTERED INTO THESE TINY HOLES AND BEGAN THE DISBONDING. IF THESE SHEATH DELAMS WERE WITHIN THE ALLOWABLE REPAIR LIMITS; THEN; BY APPLYING THE ADHESIVE UNDER THE SHEATH GUARD; USING THE SERVICE BULLETIN GUIDELINES; THE OPERATOR COULD GET ANOTHER 500 HOURS OF PROP SERVICE LIFE. BY THEN; MOST PROP BLADES WOULD BE REMOVED FOR OVERHAUL. THE OVERHAUL PROCESS INCLUDED THE REMOVAL OF THE OLD NICKEL SHEATH GUARD ON THE BLADE AND INSTALLING A NEW UNDAMAGED SHEATH THAT DID NOT HAVE THE PREVIOUS MANUFACTURING FLAWS. NEW PART NUMBERS WERE GIVEN TO THESE OVERHAULED BLADES; BUT THE SERIAL NUMBERS REMAINED THE SAME. REPORTER STATED HIS CARRIER IS NOW SEEING SIMILAR TYPE DISBONDING OF EVEN THE NEW OVERHAULED DOWTY PROP BLADE SHEATHS. REPORTER ALSO STATED MANY TIMES THE MAINT PROGRAM TASK CARDS ARE NOT CURRENT OR APPLICABLE TO THE UNIT OR PROP BLADE BEING CALLED OUT FOR MAINT. THE MAINT PROGRAM ROUTINELY TRANSPOSES ZERO'S FOR THE ALPHABETICAL LETTER 'O' IN THE DOCUMENTS; OR THE REVERSE.