What material issues arise in aging aircraft and how are they addressed?

Aging aircraft experience material degradation requiring continued airworthiness programs. Issues: Fatigue - Crack initiation and growth at stress concentrations, fastener holes, joints; Corrosion - Pitting progressing to cracks, exfoliation, environmental attack; Widespread Fatigue Damage (WFD) - Multiple cracks in same structural element; and Obsolescence - Materials/processes no longer available. Programs: Supplemental Structural Inspection Program (SSIP) - Enhanced inspections beyond baseline; Aging Aircraft Safety Rule (AASR) - FAR 26 requirements; Continued Operational Safety (COS) - Ongoing assessment; and Repair Assessment - Existing repairs evaluated. Analysis: Updated fatigue analysis with actual usage, Damage tolerance reassessment, Corrosion protection program, and Structure sampling (teardown inspection). Material considerations: Original material specifications may not reflect current properties, Replacement materials must be equivalent, and Repair materials compatibility. Limit of Validity (LOV) establishes maximum operational life. Beyond LOV requires additional substantiation or retirement. Economic analysis balances inspection/repair cost against replacement.