This advisory circular (AC) provides guidanc~ for compliance with the provisions of Title 14, Code of Federal Regulations (14 CFR) part 25, pertaining to the requirements for damage-tolerance and fatigue evaluation oftransport category aircraft structurce, including evaluation of widespread fatigue dam, age (VlFD) and establishing a limit of validity of the engineering data that supports the structural-maintenance program (hereafter referred to as the LOV).