A BE90; DURING A TURB ENCOUNTER INSPECTION WAS FOUND TO HAVE THE WING UPPER FORWARD MOUNT BOLTS TORQUE CHKED WITH AN UNCALIBRATED TORQUE WRENCH.

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WHILE PERFORMING AN 'INSPECTION AFTER ENCOUNTERING TURB' ON A USDA FOREST SVC FIRE FIGHTING ACFT; AS THE WING UPPER FORWARD MOUNT BOLTS AND NUTS WERE BEING TORQUED; THE TORQUE WRENCH BEING USED BROKE. ANOTHER TORQUE WRENCH WAS OBTAINED; BUT IT WAS NOTICED THAT IT WAS OUT OF CALIBRATION. MYSELF AND THE TECHNICIAN WHO WAS PERFORMING THE WORK DISCUSSED THIS AND 'RATIONALIZED' THAT 'IT WAS ONLY OUT OF CALIBRATION BY A MONTH OF TWO.' IT WAS DECIDED TO CONTINUE WITH THE PROC WITH THE OUT OF CALIBRATION TORQUE WRENCH. WHEN BROUGHT TO MY ATTN YESTERDAY EVENING I IMMEDIATELY ARRANGED TO HAVE THE ACFT GNDED AND A TORQUE CHK DONE. I DON'T WANT TO SOUND LIKE I'M MAKING EXCUSES; BUT I BELIEVE THIS OCCURRENCE IS A RESULT OF FATIGUE AND STRESS. DURING THE PREVIOUS 7 DAYS; BOTH MYSELF AND THE OTHER TECHNICIAN HAD WORKED MANY LONG HRS. OVER THE PREVIOUS 30 DAYS I HAVE HAD 3 DAYS OFF. ON MY PART; A HIGH DEGREE OF STRESS WAS ALSO FELT RESULTING FROM THE DISCOVERY THAT THESE BOLTS HAD PREVIOUSLY BEEN IMPROPERLY INSTALLED APPROX 110 HRS BEFORE BY ONE SHOP; AND THAT A RE-TORQUE CHK HAD BEEN ACCOMPLISHED ABOUT 70 HRS AFTER THAT BY ANOTHER SHOP. IF THE ACFT HAD NOT FLOWN THROUGH THE TURB; RESULTING IN THE NEED FOR THE TURB INSPECTION; THIS ACFT WOULD NOT HAVE HAD THESE BOLTS CHKED FOR ANOTHER 900 HRS; WHICH WOULD HAVE UNDOUBTEDLY RESULTED IN THE LOSS OF ONE OF MY PLTS AND THE ACFT. IN HINDSIGHT; I SHOULD HAVE RECOGNIZED THEN THAT I WAS BADLY IN NEED OF SOME REST. INSTEAD; I PRESSED ON. WHILE I WAS NOT PERSONALLY PERFORMING THIS WORK I FEEL RESPONSIBLE FOR THIS MISTAKE; AS I WAS PROBABLY INSTRUMENTAL IN CONVINCING THE TECHNICIAN WHO WAS; INTO USING THE UN-CALIBRATED TORQUE WRENCH. I HAVE ADVISED HIM TO ALSO SUBMIT A RPT.