Narrative:

Aircraft X had a 12000 cycle pylon inspection scheduled on the r-hand pylon. The work was performed per company procedures. This procedure stipulates 'fluorescent-penetrant inspect the aft cone; bolt or remove and replace with new or overhauled.' a new aft engine mount isolator was installed. I observed a mechanic verify the step of the maintenance procedure checking the self-locking feature of the thrust link mount (18 inch/pounds) and then proceeded to observe the mechanic torque the aft mount isolator. I asked him if he set the torque wrench to 31 ft/pounds (per company procedures). He replied that he did so. The mechanic who checked the break-away torque on the aft thrust-link barrel-nuts for 18 inch/pounds; set the torque wrench used on the same toolbox. I watched the mechanic torque the isolator in the prescribed manner and heard the audible click when the torque was reached. Just after asking the mechanic if he set the torque wrench to 31 ft/pounds; another mechanic working on the engine asked me if I was done inspecting the forward part of the pylon and I replied that I did so. Today a mechanic approached me and said that he laid down the inch-pound torque wrench on the toolbox and he wasn't sure which torque wrench was used; the inch-pound or the ft-pound. He contacted the mechanic who was at home on his day off; and was not sure as to which torque wrench he used. I was distraction by the other mechanic asking me a question; and just asked verbally if the torque was set at 31 ft-pounds and did not visually verify it. This could result in an under-torque for the isolator mount bolts. As soon as I found out I contacted my supervisor who contacted maintenance control and informed them of the potential problem; and they proceeded to take the aircraft OTS until the situation is rectified. As previously stated; company maintenance procedure stipulates that 'the aft-cone bolt should be fluorescent-penetrant inspected or removed and replaced with a new or overhauled unit.' a non-routine card was not used; thinking that this procedure covers the installation. My supervisor informed me that a non-routine card should have been used to cover the installation instead of the company maintenance form. In retrospect; I should not have trusted the mechanic when he verbally assured me that the torque was set at 31 ft pounds; and should have visually checked the torque-wrench. I realize the ramifications of this event and the trouble caused to the company and a potentially unsafe situation. I took all the steps I could to remedy the situation; and in the future; I will not let distrs interfere with performing a verbal and visual check of the torque wrench. Supplemental information from acn 750430: aircraft #2 engine 12K inspection. I used wrong torque unit for aft engine isolation mount bolts. Instead of using 'pounds;' I used 'inches' for the torque amount. This happened due to lack of communication. I also discovered one more problem. There is no document/nr's written up for this isolation mount. After all the jobs we have completed for this engine; I checked all paperwork; except the aft engine isolation mount which wasn't documented. Supplemental information from acn 749987: I came to work at night and overheard that the aft cone bolt isolator had been under torqued. I also heard that there was never an nrc wrote to replace the aft cone bolt.

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Original NASA ASRS Text

Title: A B737-300 #2 ENG AFT MOUNT ISOLATOR ASSEMBLY WAS UNDER TORQUED. AN 'INCH' POUND CALIBRATED TORQUE WRENCH WAS USED INSTEAD OF A 'FOOT' POUND.

Narrative: ACFT X HAD A 12000 CYCLE PYLON INSPECTION SCHEDULED ON THE R-HAND PYLON. THE WORK WAS PERFORMED PER COMPANY PROCS. THIS PROC STIPULATES 'FLUORESCENT-PENETRANT INSPECT THE AFT CONE; BOLT OR REMOVE AND REPLACE WITH NEW OR OVERHAULED.' A NEW AFT ENG MOUNT ISOLATOR WAS INSTALLED. I OBSERVED A MECH VERIFY THE STEP OF THE MAINT PROC CHKING THE SELF-LOCKING FEATURE OF THE THRUST LINK MOUNT (18 INCH/LBS) AND THEN PROCEEDED TO OBSERVE THE MECH TORQUE THE AFT MOUNT ISOLATOR. I ASKED HIM IF HE SET THE TORQUE WRENCH TO 31 FT/LBS (PER COMPANY PROCS). HE REPLIED THAT HE DID SO. THE MECH WHO CHKED THE BREAK-AWAY TORQUE ON THE AFT THRUST-LINK BARREL-NUTS FOR 18 INCH/LBS; SET THE TORQUE WRENCH USED ON THE SAME TOOLBOX. I WATCHED THE MECH TORQUE THE ISOLATOR IN THE PRESCRIBED MANNER AND HEARD THE AUDIBLE CLICK WHEN THE TORQUE WAS REACHED. JUST AFTER ASKING THE MECH IF HE SET THE TORQUE WRENCH TO 31 FT/LBS; ANOTHER MECH WORKING ON THE ENG ASKED ME IF I WAS DONE INSPECTING THE FORWARD PART OF THE PYLON AND I REPLIED THAT I DID SO. TODAY A MECH APCHED ME AND SAID THAT HE LAID DOWN THE INCH-LB TORQUE WRENCH ON THE TOOLBOX AND HE WASN'T SURE WHICH TORQUE WRENCH WAS USED; THE INCH-LB OR THE FT-LB. HE CONTACTED THE MECH WHO WAS AT HOME ON HIS DAY OFF; AND WAS NOT SURE AS TO WHICH TORQUE WRENCH HE USED. I WAS DISTR BY THE OTHER MECH ASKING ME A QUESTION; AND JUST ASKED VERBALLY IF THE TORQUE WAS SET AT 31 FT-LBS AND DID NOT VISUALLY VERIFY IT. THIS COULD RESULT IN AN UNDER-TORQUE FOR THE ISOLATOR MOUNT BOLTS. AS SOON AS I FOUND OUT I CONTACTED MY SUPVR WHO CONTACTED MAINT CTL AND INFORMED THEM OF THE POTENTIAL PROB; AND THEY PROCEEDED TO TAKE THE ACFT OTS UNTIL THE SITUATION IS RECTIFIED. AS PREVIOUSLY STATED; COMPANY MAINT PROC STIPULATES THAT 'THE AFT-CONE BOLT SHOULD BE FLUORESCENT-PENETRANT INSPECTED OR REMOVED AND REPLACED WITH A NEW OR OVERHAULED UNIT.' A NON-ROUTINE CARD WAS NOT USED; THINKING THAT THIS PROC COVERS THE INSTALLATION. MY SUPVR INFORMED ME THAT A NON-ROUTINE CARD SHOULD HAVE BEEN USED TO COVER THE INSTALLATION INSTEAD OF THE COMPANY MAINT FORM. IN RETROSPECT; I SHOULD NOT HAVE TRUSTED THE MECH WHEN HE VERBALLY ASSURED ME THAT THE TORQUE WAS SET AT 31 FT LBS; AND SHOULD HAVE VISUALLY CHKED THE TORQUE-WRENCH. I REALIZE THE RAMIFICATIONS OF THIS EVENT AND THE TROUBLE CAUSED TO THE COMPANY AND A POTENTIALLY UNSAFE SITUATION. I TOOK ALL THE STEPS I COULD TO REMEDY THE SITUATION; AND IN THE FUTURE; I WILL NOT LET DISTRS INTERFERE WITH PERFORMING A VERBAL AND VISUAL CHK OF THE TORQUE WRENCH. SUPPLEMENTAL INFO FROM ACN 750430: ACFT #2 ENG 12K INSPECTION. I USED WRONG TORQUE UNIT FOR AFT ENG ISOLATION MOUNT BOLTS. INSTEAD OF USING 'LBS;' I USED 'INCHES' FOR THE TORQUE AMOUNT. THIS HAPPENED DUE TO LACK OF COM. I ALSO DISCOVERED ONE MORE PROB. THERE IS NO DOCUMENT/NR'S WRITTEN UP FOR THIS ISOLATION MOUNT. AFTER ALL THE JOBS WE HAVE COMPLETED FOR THIS ENG; I CHKED ALL PAPERWORK; EXCEPT THE AFT ENG ISOLATION MOUNT WHICH WASN'T DOCUMENTED. SUPPLEMENTAL INFO FROM ACN 749987: I CAME TO WORK AT NIGHT AND OVERHEARD THAT THE AFT CONE BOLT ISOLATOR HAD BEEN UNDER TORQUED. I ALSO HEARD THAT THERE WAS NEVER AN NRC WROTE TO REPLACE THE AFT CONE BOLT.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.