AFTER REVIEWING AN ATR-72 LOGBOOK AND PAPERWORK WITH A LEFT ENG IMPELLER DAMAGE MIGRATING; REQUIRING AN ENG REMOVAL IN 10 HOURS; AN INSPECTOR INFORMS THE MAINT SUPERVISOR THE AIRWORTHINESS RELEASE COULD NOT BE SIGNED-OFF.

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THE DECISION TO OVERRIDE THE FIRST INITIAL 10 HR RECOMMENDED BY PRATT AND WHITNEY MAINT MANUAL BY THE SUPVR WAS DONE WITHOUT A SECOND INSPECTION OF THE DAMAGE IMPELLER. AND ANOTHER 100-200 HRS WAS ADDED TO THE INSPECTION TIME; AND WHEN CAME DUE FOR ANOTHER INSPECTION IN SEPTEMBER THE DECISION WAS MADE TO BLOW OFF THE INSPECTION A SECOND TIME. NO ONE HAS CHKED TO SEE HOW MUCH WORSE THE DAMAGE HAD GOT. SEE PRATT AND WHITNEY MANUAL PAGE 608C; 608D; AND 608E TABLE 602. IN ACCORDANCE WITH P&W MAINT MANUAL; UPON INITIAL INSPECTION; IF A DAMAGE IS FOUND; RECORD THE TYPE AND SIZE OF THE DAMAGE. A SUBSEQUENT INSPECTION MUST BE DONE IN 100 HRS AND NOT TO EXCEED 200 HRS. THIS INITIAL FINDING WAS DONE IN AUGUST BY EMPLOYEE X. THE SIZE OF THE DAMAGE WAS 0.068. LATER IN AUGUST; A SUBSEQUENT INSPECTION WAS DONE AND THE SIZE RECORDED WAS 0.105. AS PER P&W THE ENG MUST BE REMOVED IN 10 HRS. THE 10 HRS CAME AND WENT AND ANOTHER 200 HRS WAS ADDED TO THE ENG. 1) A CLR VIOLATION TO P&W MANUAL; 2) NO ONE DID ANOTHER INSPECTION TO EVEN DETERMINE IF THE ENG CAN CONTINUE IN SVC -- THEY JUST ADD THE 200 HRS TO THE ENG TIME. IN SEPTEMBER WHEN IT CAME DUE AGAIN; SOMEONE MADE THE DECISION TO NOT INSPECT THE ENG FOR A SECOND TIME! I WAS THE INSPECTOR ON DUTY AND THE ACFT LOGBOOK AND PAPERWORK WAS REVIEWED BY ME; I REVIEWED THE PAPERWORK BUT I TOLD THE MAINT SUPVR I CAN'T SIGN THE AIRWORTHINESS RELEASE BECAUSE I FELT THAT IT WILL BE FALSE STATEMENT. THE MAINT SUPVR ACTUALLY GRABBED ME TRYING TO PUSH ME TO SIT IN A CHAIR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE DAMAGED ENGINE IMPELLER WAS FOUND CRACKED DURING A BOROSCOPE INSPECTION; USING A COMPARISON TYPE METHOD THAT INCLUDES USING DATA FROM THE ENGINE MANUFACTURER AND COMPARING THAT DATA TO THE DAMAGED IMPELLER. AN ALTERNATE BOROSCOPE PROCEDURE WOULD BE THE STEREO METHOD; TAKING MEASUREMENTS FROM TWO DIFFERENT ANGLES. REPORTER STATED NONE OF THEM (INSPECTORS) ARE TRAINED IN THAT METHOD. THE LEFT ENG ON THE ATR-72 HAD ALREADY EXCEEDED THE ALLOWABLE 10 HOURS AND REQUIRED REMOVAL DUE TO THE CONTINUED MIGRATION OF DAMAGE ON THE IMPELLER. REPORTER STATED; UNLESS WRITTEN AUTHORIZATION ALLOWING CONTINUED OPERATION OF THE DAMAGED ENGINE CAME FROM THE MANUFACTURER; OR CARRIER ENGINEERING DEPT; HE COULD NOT SIGN THE MAINT AIRWORTHINESS RELEASE; BECAUSE HE FELT THAT WOULD BE A FALSE STATEMENT. REPORTER STATED THE MAINT SUPERVISOR WAS VERY ANGRY. THE ACFT WAS SOMEHOW STILL RELEASED FOR SERVICE WITHOUT THE ENGINE BEING REINSPECTED FOR CONTINUED MIGRATION OF THE IMPELLER CRACK.