What was found
RETURN TO FIELD DUE TO BIRD STRIKE TO NR 2 ENGINE & ASSOCIATED HIGH VIBRATIONS. AFTER FAN BLADE SET REPLACEMENT HIGH ENGINE VIBRATION CONTINUED AND ENGINE WAS REPLACED. THE ENGINE SHOP VERIFIED CORRECT FAN BLADE SPACER, SHIM, RETAINER AND PROPER FAN BLADE WEIGHT CLASS POSITIONING INSTALLATION (38 FAN BLADES). WHILE VERIFYING FAN BLADE WEIGHT CLASS MATCH TO THEIR ACTUAL MOMENT WEIGHT, ONE FAN BLADE WAS FOUND MISS-MARKED BY VENDOR BY MORE THAN SEVERAL CLASSES. VERIFIED THE MISS-MARKED MOMENT WEIGHT CLASS ON FAN BLADE AS CAUSE FOR ENGINE HIGH FAN VIBRATION.