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Quantitative risk assessment (QRA) is now required by most aircraft structural integrityprograms. One of the key components of an accurate QRA resides in the accuracy of the fracturemechanics modelling of multiple site fatigue damage (MSD) scenarios, which is used to generatethe MSD crack growth curves.This paper presents the results on the development of fracture mechanics models for MSDproblems in order to carry out a QRA. To address this complex problem, NRC developed a crackgrowth analysis (CGA) software, which is capable of calculating the β-solutions for stressintensity factors and the remaining life of MSD in built-up structures (aircraft wing panels). Theβ-solutions were calculated by superposition of several closed-form and numerical solutions.Comparison between NRC’s CGA β-solutions and p-version finite element analysis (FEA) resultsfor various MSD scenarios are presented in this paper. Good agreement was obtained betweenNRC’s CGA results and FEA results