What was found
MCN - MAJOR REPAIR - DURING C-04 CHECK FILIFORM CORROSION WAS FOUND ON UPPER SURFACE OF FLOOR SUPPORT BEAM Y-254, AFT OF FR 16. MAINTENANCE REMOVED CORROSION AND FOUND MATERIAL LOSS TO BE OUT OF LIMITS. REMOVED FLOOR SUPPORT BEAM Y-254 FROM FR 12 TO FR 21; FABRICATED A NEW REPLACEMENT FLOOR SUPPORT BEAM; INSTALLED REPAIR PART IAW A320 SRM 51-42-11 PG 28-33, 39, & 41, FIG 12, 13, & 18.