What was found
DURING 'C' CHECK, MAINTENANCE FOUND CENTER WING BOX UPPER SKIN FS 825, RBL 55-46 COMMON TO STRINGER 9 AFTER EXISTING CORRODED DOUBLER WAS REMOVED, SKIN WAS FOUND TO BE BEYOND LIMITS. INSTALLED REPAIR IAW DHC SK915-577 AND UPS ENGINE. FILE NR 727-57-1071.