Past experience has shown that during the operational life of an aircraft structure cracks or failures may arise in different structural components. In future designs the designer must be able on the one hand to restrict the occurrence of cracks by a careful detail design and on the other hand to guarantee some specified life of the aircraft if cracks nevertheless may arise. The object of this paper is to give the designer some support in this task. Because the major part of the aircraft structure consists of sheet structiires, the attention will be mainly focussed on this structural configuration. The paper discusses briefly the different analyses that are relevant to the design of a fail-safe aircraft structure; the static strength, the crack initiation and propagation and the residual straigth analyses. The main part of the paper will be devoted to the application of fracture mechanics in the crack propagation and residual strength analyses. Theoretical results of an investigation carried out at NLR in this field and verification of these results by experiments will be shown. Finally the paper will provide some guidelines for aircraft structural applications.