Air carrier technicians reported that they installed the fan blades incorrectly which caused a high vibration on the engine while on the ground.
Synopsis
Air carrier technicians reported that they installed the fan blades incorrectly which caused a high vibration on the engine while on the ground.
Narrative
On the Day 0; I was called as the Inspector for Aircraft X blade lube card. After receiving the call I looked on the computer to see if there was any issues with this job card I was about to inspect. Upon looking at the job card I didn't see any issues Non routine s or turnovers that would prevent me from conducting the inspection. I gathered the tooling I normally use when conducting a blade lube inspection and went out to the aircraft. Upon arriving at the aircraft I noticed the Blades had already been removed and lubed; there were(2) Mechanics at the aircraft when I arrived. I asked if they removed the blades and they said NO; the previous shift removed the blades and presumably cleaned and lubed the blades as well. I asked if they knew if those guys were still there; the answer was NO; So I asked them where were they help; Because over at the line there's a minimum of (4) Mechanics doing this task. They told me it was only the (2) of them. I said okay have either one of you done this task before and the answer was No. I said okay and told them I was going to do my Pre inspection of the Blades and hub/disk since I did not witness the removal cleaning or lubing of the blades. I noticed the fan blades were not arranged in sequential order on the blade rack; The mechanics noticed this as well I told them that they were supposed to be in order. I moved on to the engine itself and noticed the hub/disk was also marked but not in a sequential order. I told the Mechanics that only the blades were to be marked and arranged on the blade rack in sequential order. I asked the mechanics did either of the witness the removal of the blades and who marked them and the hub/disk; The answer was No. Since the blades and hub/disk were both marked I assumed that the Removal Crew removed each blade and marked the blade and hub/disk where it was removed from but did not arrange the blades on the rack in sequential order or removed them in sequential order for whatever reason; I do not know. And since there was no issues with the blades or mapping I saw no reason not to reinstall the blades where they were marked on the hub/disk. I located the Number 1 blade on the blade rack and the location where it was to be installed on the hub/disk and told the Mechanics to reinstall the remaining blades on the position where they were marked on the hub/disk. I also marked the rear spinner cone with a piece of yellow tape noting the dimple and where it was to be aligned and installed after all the blades were reinstalled. I watched the complete Installation and had no issues with the reinstallation besides having to locate the unarranged blades on the blade rack and match it to the location marked on the hub/disk. The remainder of the installation went without any issues; it took close to 3 hrs because there were only (2) Mechanics who had never done the task before so there was a lot of on the job training. Along the way. I had no ideal that the markings on the hub/disk were not where the blades were supposed to be installed and have never had an incident like this before; as since last year when I was a Line Inspector I completed several blade lube inspections and several more prior to that never with any incidents. I told the Mechanics that they did a good job and thanked them. I also told them at the very beginning of this task to take their time so there would not be any mistakes on either part. Thats why it took longer than usual. I stamped my portion of the required inspection item (RII) and went back to the Inspectors office. I wasn't notified of this incident until Day 0 and told that needed to complete a report because of such. I had assumed that the engine would under go an engine run to verify the reinstallation of the fan blade before it was released back into an airworthy condition. If memory serves engine runs were conducted on the Line when I was there. It just make good sense in my humble opinion. This is all that I can recall at this time.Please call Text or Email with any other questions.Cause: The numbering on the blades and hub I believe caused this Incident along with no narrative on why the hub/disk was marked period. Example a Turnover or Non Routine or something to notify the incoming crew Inspector and mechanics on why both the blades and the hub/disk were marked. If I had that information I would have re-installed the fan blades as I have on previous blade lube inspections tasks without any issues. Suggestions: Whenever possible have the same Crew Inspector and mechanics perform the complete blade lube job card; I believe that will definitely alleviate any mistakes like this again; And also if there are any abnormalities such as the blades and the hub/disk both being marked do not leave any markings on the hub/disk. And leave a Turnover as well.Also; on the job card it should be re-vised to say sequential order instead of related slots.
Second reporter narrative
I was given a job card which included installation of Engine Fan Blades for #2 Engine on Aircraft X. Blades already removed and lubricated prior to reinstallation. I was given the task to install the blades with my mechanic partner for the night and it is and required inspection item (RII) item and we had called in an inspector prior to beginning the job to witness the job to be accomplished. When entering the inlet we saw that the blade hub had numbers written near the recess where the blades are to be installed in 180 degree apart example #1 in the 12o'clock position and 2 in the 6o'clock position. The job card and figure drawing was showing to install them starting at the 6o'clock position due to weight of the blade. When looking at the numbers being offset by 180 degrees on the hub we believe we understood to install the blades 180 degrees to each other and match the numbers written on the blade while moving counter clockwise following the marked numbers we saw on the hub. We reviewed the Aircraft Maintenance Manual (AMM) as well for fan blade installation with a caution statement about the blades being in pairs. We believed we understood that numbers associated with the pairs on the hub where how they where removed initially and re installed according to the numbers on both the fan blade and hub and matched accordingly. We asked our inspector if this was being done correctly for me and my partner have not done the job before. When showing the way we understood installing the blades into the fan blade hub together he prompted to continue forward and ultimately approved the work being performed so we continued as such. We find out later on in the month that the aircraft came back from flight crew report due to high vibration on the ground. The plane came back to base and the problem was corrected promptly at base by another crew of mechanics.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.