Narrative:

During a routine fan blade lube, during an overnight check, 1 damper was left out under #20 blade. The aircraft left the station (ZZZ) on a revenue flight the next morning, and upon reaching xzx, the pilot wrote up a vibration on #2 engine at 83% N1 and 75% N1. A mechanic in xzx performed another fan blade lube (suspecting the damper missing from the previous night's fan lube). Found the missing damper, installed a new one and corrected the problem. 2 of us worked together that night on the fan lube. My partner cleaned and resprayed the dampers. Unknown to him, 1 damper fell off the shelf where he was working and landed on a lower portion of the work table, out of sight. Upon reassembly, I sat in the inlet installing blades and dampers. Apparently I missed installing a damper under #20 fan blade. This occurs occasionally, and you'll have an extra damper left over, after all the fan blades are installed. Then you spin the fan slowly and find where the missing damper is, and install it. But in this case, we had no 'extra' damper because it had fallen to a lower shelf on the work table unknown to us. Inspection looked over the blade installation (they don't look at dampers) and gave us an ok to install front spinners. I think the major factor in this instance was alertness. The human body is not designed to work from XA00 to XI00. I cannot function at my best during the night. I routinely get 4 hours of restless sleep a day, and I'm constantly tired and irritable. The second factor is complacency. Performing the same tasks night after night in a third shift environment leads to complacent performance. In the future, however, I will endeavor to perform my tasks in a more diligent and alert manner. This event did not cause any aircraft damage, personal injury or flight diversion. Just rework at the next station.

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Original NASA ASRS Text

Title: A B737-300 WAS DISPATCHED AFTER A #2 ENG FAN LUBRICATION WITH 1 DAMPER MISSING FROM #20 BLADE CAUSING ENG VIBRATION.

Narrative: DURING A ROUTINE FAN BLADE LUBE, DURING AN OVERNIGHT CHK, 1 DAMPER WAS LEFT OUT UNDER #20 BLADE. THE ACFT LEFT THE STATION (ZZZ) ON A REVENUE FLT THE NEXT MORNING, AND UPON REACHING XZX, THE PLT WROTE UP A VIBRATION ON #2 ENG AT 83% N1 AND 75% N1. A MECH IN XZX PERFORMED ANOTHER FAN BLADE LUBE (SUSPECTING THE DAMPER MISSING FROM THE PREVIOUS NIGHT'S FAN LUBE). FOUND THE MISSING DAMPER, INSTALLED A NEW ONE AND CORRECTED THE PROB. 2 OF US WORKED TOGETHER THAT NIGHT ON THE FAN LUBE. MY PARTNER CLEANED AND RESPRAYED THE DAMPERS. UNKNOWN TO HIM, 1 DAMPER FELL OFF THE SHELF WHERE HE WAS WORKING AND LANDED ON A LOWER PORTION OF THE WORK TABLE, OUT OF SIGHT. UPON REASSEMBLY, I SAT IN THE INLET INSTALLING BLADES AND DAMPERS. APPARENTLY I MISSED INSTALLING A DAMPER UNDER #20 FAN BLADE. THIS OCCURS OCCASIONALLY, AND YOU'LL HAVE AN EXTRA DAMPER LEFT OVER, AFTER ALL THE FAN BLADES ARE INSTALLED. THEN YOU SPIN THE FAN SLOWLY AND FIND WHERE THE MISSING DAMPER IS, AND INSTALL IT. BUT IN THIS CASE, WE HAD NO 'EXTRA' DAMPER BECAUSE IT HAD FALLEN TO A LOWER SHELF ON THE WORK TABLE UNKNOWN TO US. INSPECTION LOOKED OVER THE BLADE INSTALLATION (THEY DON'T LOOK AT DAMPERS) AND GAVE US AN OK TO INSTALL FRONT SPINNERS. I THINK THE MAJOR FACTOR IN THIS INSTANCE WAS ALERTNESS. THE HUMAN BODY IS NOT DESIGNED TO WORK FROM XA00 TO XI00. I CANNOT FUNCTION AT MY BEST DURING THE NIGHT. I ROUTINELY GET 4 HRS OF RESTLESS SLEEP A DAY, AND I'M CONSTANTLY TIRED AND IRRITABLE. THE SECOND FACTOR IS COMPLACENCY. PERFORMING THE SAME TASKS NIGHT AFTER NIGHT IN A THIRD SHIFT ENVIRONMENT LEADS TO COMPLACENT PERFORMANCE. IN THE FUTURE, HOWEVER, I WILL ENDEAVOR TO PERFORM MY TASKS IN A MORE DILIGENT AND ALERT MANNER. THIS EVENT DID NOT CAUSE ANY ACFT DAMAGE, PERSONAL INJURY OR FLT DIVERSION. JUST REWORK AT THE NEXT STATION.

Data retrieved from NASA's ASRS site as of July 2007 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.