How do you address Widespread Fatigue Damage (WFD) in aging aircraft structures?

WFD occurs when multiple fatigue cracks at adjacent structural details develop and interact, potentially causing loss of fail-safe capability. Addressing WFD requires: Identifying susceptible structure through analysis (lap splices, skin panels, frame bays), establishing Limit of Validity (LOV) per FAR 25.571 Amendment 96 beyond which WFD is expected, developing inspection programs to detect MSD (Multiple Site Damage) and MED (Multiple Element Damage), determining DSG (Design Service Goal) and ESG (Extended Service Goal), and implementing modifications or retirement schedules. Analysis uses probabilistic methods accounting for crack population statistics. Aloha Airlines Flight 243 (1988) drove regulatory focus on WFD.