Narrative:

On jun/sun/04, aircraft X arrived at ZZZ and mr X and I were assigned a 3 service and fan blade change. I began the service check and when mr X's shift started I had most of the outside of the check completed. When mr X arrived at the aircraft we discussed our work assignment, changing a double set of fan blades on engine #1 and a #1 main tire change. We changed the tire and I started the blade removal while mr X continued with the 3 service. As I removed the parts to reach the blades, mr X stopped working the 3 service and began getting the 2 blade set boxes and unpacking them. I had read the maintenance manual before the aircraft had arrived and felt I had an understanding of the removal and installation, including the fact that the individual blades in each set were to be installed 180 degrees from one another. After removing the blades and handing them to mr X, the old blades were placed in the box lids, new blades were removed from the box and placed on a lift truck bed for lubricating per the maintenance manual. Before starting the lubrication procedure, we marked each blade with the fan position number. Because the blades were marked with incorrect position numbers, I installed them together, rather than 180 degrees apart. I verified that the installation was correct by blade position number and did not rechk the blade weights. We completed the blade installation per the maintenance manual. Mr X commented that he would feel better if the engine was run, but since the maintenance manual does not require a run for 2 sets of blades, the run was not performed. Supplemental information from acn 627104: the air carrier has instituted a fan blade training program. And also labeled fan blade boxes with placards to install the fan blade 180 degrees apart.

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Original NASA ASRS Text

Title: B737-500 CAPT RETURNED TO THE DEP ARPT WITH EXCESSIVE ENG VIBRATION AFTER THE MECHS CHANGED SOME FAN BLADES.

Narrative: ON JUN/SUN/04, ACFT X ARRIVED AT ZZZ AND MR X AND I WERE ASSIGNED A 3 SVC AND FAN BLADE CHANGE. I BEGAN THE SVC CHK AND WHEN MR X'S SHIFT STARTED I HAD MOST OF THE OUTSIDE OF THE CHK COMPLETED. WHEN MR X ARRIVED AT THE ACFT WE DISCUSSED OUR WORK ASSIGNMENT, CHANGING A DOUBLE SET OF FAN BLADES ON ENG #1 AND A #1 MAIN TIRE CHANGE. WE CHANGED THE TIRE AND I STARTED THE BLADE REMOVAL WHILE MR X CONTINUED WITH THE 3 SVC. AS I REMOVED THE PARTS TO REACH THE BLADES, MR X STOPPED WORKING THE 3 SVC AND BEGAN GETTING THE 2 BLADE SET BOXES AND UNPACKING THEM. I HAD READ THE MAINT MANUAL BEFORE THE ACFT HAD ARRIVED AND FELT I HAD AN UNDERSTANDING OF THE REMOVAL AND INSTALLATION, INCLUDING THE FACT THAT THE INDIVIDUAL BLADES IN EACH SET WERE TO BE INSTALLED 180 DEGS FROM ONE ANOTHER. AFTER REMOVING THE BLADES AND HANDING THEM TO MR X, THE OLD BLADES WERE PLACED IN THE BOX LIDS, NEW BLADES WERE REMOVED FROM THE BOX AND PLACED ON A LIFT TRUCK BED FOR LUBRICATING PER THE MAINT MANUAL. BEFORE STARTING THE LUBRICATION PROC, WE MARKED EACH BLADE WITH THE FAN POS NUMBER. BECAUSE THE BLADES WERE MARKED WITH INCORRECT POS NUMBERS, I INSTALLED THEM TOGETHER, RATHER THAN 180 DEGS APART. I VERIFIED THAT THE INSTALLATION WAS CORRECT BY BLADE POS NUMBER AND DID NOT RECHK THE BLADE WTS. WE COMPLETED THE BLADE INSTALLATION PER THE MAINT MANUAL. MR X COMMENTED THAT HE WOULD FEEL BETTER IF THE ENG WAS RUN, BUT SINCE THE MAINT MANUAL DOES NOT REQUIRE A RUN FOR 2 SETS OF BLADES, THE RUN WAS NOT PERFORMED. SUPPLEMENTAL INFO FROM ACN 627104: THE ACR HAS INSTITUTED A FAN BLADE TRAINING PROGRAM. AND ALSO LABELED FAN BLADE BOXES WITH PLACARDS TO INSTALL THE FAN BLADE 180 DEGS APART.

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.