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In this paper a study of a Superplastic Formed/Diffusion Bonded(SPF/DB) aircraft wing section under working load is presented. Such structuresoperate under cycle load, therefore fatigue has to be considered. The presence ofcracks has to be included since damages can occur either in production or during theoperating life. The damaged structure is then considered and the stress intensity fac-tors are evaluated for cracks of different sizes. Considering a load cycle which spanfrom 0 to maximum load, the relationships between the stress intensity factor and thecriteria for fatigue-life prediction and crack growth directions is soon derived. Theaim of this work is to demonstrate the effectiveness of the boundary element methodto investigate behaviour of cracks in complex large scale structures in presence ofdamages.