An Inspector and Line Mechanic report on their involvement with # 1 engine fan blade replacements on a B737-700; after the aircraft had previously diverted for engine vibration from a bird strike.
Synopsis
An Inspector and Line Mechanic report on their involvement with # 1 engine fan blade replacements on a B737-700; after the aircraft had previously diverted for engine vibration from a bird strike.
Narrative
I reported to work on overtime for day shift. Upon arrival I was told that I would be the Inspector for aircraft #1 engine fan blade change due to bird strike that occurred on the previous day; taking it out of service. I then got a turn over from the Routine Overnight Inspector (RON) Inspector; who showed me the maintenance manual references and maintenance task cards that were used and up to what step they got to. He also showed a card that required a sign off; after completed fan blade installation and engine run; after borescope. Inspected borescope. Two Mechanics were working the blade installation; following step by step the maintenance manual references. I confirmed the new fan blade weights; with the fan blade plot paper work matched and also called Maintenance Control regarding spinner weights. I then inspected the fan blade platform pins per the maintenance manual task. (Which consisted of the fan blade retainer; mid flange of the fan disk; and forward flange of the booster spool?) I then stamped my number on four steps that were completed with per maintenance manual. The following steps were to install fan blades. I gave a turnover; since he was the Inspector taking over; informing him that the two mechanics were following the maintenance manual and lubricating the blades and spacers per maintenance manual and that they had the OK to install. I went home. I was told later that aircraft had to divert due to high engine vibration.
Second reporter narrative
Aircraft had a diversion due to high #1 engine vibration. Aircraft had a bird strike on the #1 engine and damaged several blades and platforms. I was assigned with another Mechanic to clean and prepare the engine for inspection. I was assigned with another Mechanic to install the new fan blades set; shims; platforms and all other parts of the fan assembly previously removed. Everything was installed per the maintenance task card and applicable Maintenance Manual reference. After completion of the assembly; I was one of the Mechanics that performed the engine run and Balance Survey; as called out by the Maintenance Task and Maintenance Manual. During the engine run; #1 engine reached 3 units of vibration; compared to 1 unit on #2 engine; at the highest N1 setting. After completion of the engine run; I acquired from the airborne vibration monitor (AVM); a new balance trim solution and replaced the weights on the spinner as called for by the AVM; and documented the new installed weights on the Maintenance Task Card. The problem was fixed as documented in (our) maintenance computer syster by Mechanics; by performing another engine balance. After the fact finding meeting; it was brought to my attention that the RII inspection block on non-routine card was marked 'NO'; instead of 'YES'; and I signed the Airworthiness for aircraft.
NASA callback
Reporter stated the main concern that was raised after the B737-700 was released for service; was the failure to perform another engine run; to verify the second rebalance and vibration level was within specs; after the first engine run indicated further weight balancing was necessary. Although many Mechanics do an engine run after any blade re-balancing as a 'normal' practice; there wasn't any procedure in the paperwork Mechanics were using; to adjust the balancing weights; to do another engine run.Reporter stated his carrier has since added the engine run requirement to all their paper packages; any time the balance weights are disturbed on their CFM-56 engines.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.