N1 Vibes
As I stated in my earlier post, my knowledge of fan blade cropping was derived from personal experience on the Garrett TFE-731 fanjet engines. Even though used on some military applications, the 731 is primarily a civilian engine used on bizjets. I have not worked on CFM engines, so I cannot say what repairs are approved for that engine in it's approved M/M. (or the excerpts installed in an airline manual) Perhaps I did not make this clear enough. The requirement to crop the opposite blade in the case of cropping a blade to remove damaged material was written by engineers tasked with developing repair schemes for foriegn object damage on the 731. The "bean counters" have nothing to do with it and nothing pertinent to say about it. Engineers who have taken factors that would never be imagined by "bean counters" into account designed this repair method so that a damaged blade could be repaired rather than replaced. It is possible that mass balance was only one of the considerations and that simply adding balance weights to solve the radial imbalance did not solve all of the problems encountered when running the fan at max thrust with one cropped blade. It is also possible that removing material from two blades is less costly than buying a new blade to replace the original blade that had repairable tip damage. In any case, the engine maker has the final say as to what constitutes an approved repair. (with the certifying authority's agreement) One could request that the engine builder design and approve a repair more to one's liking if one so desired!
Best regards,
Westhawk