What was found
MCN - MAJOR REPAIR - DURING C-04 CHECK FILIFORM CORROSION WAS FOUND ON UPPER SURFACE OF FLOORBEAM Y-81 FROM FORWARD SIDE OF FR 18 TO FR 20. MAINTENANCE REMOVED CORROSION AND FOUND MATERIAL LOSS TO BE OUT OF LIMITS. REMOVED FLOORBEAM Y-81 FROM FORWARD SIDE OF FR 18 TO FR 20; FABRICATED A NEW REPLACEMENT FLOORBEAM; INSTALLED REPAIR PART IAW A320 SRM 51-42-11 PG 21-22, 28-30, 32, & 39-41, FIG 8, 12, 13 & 18.