The application of carbon fibre-resin composite to aero engine fan blades has allowed significant improvements in engine performance and weight. A number of problems involving the characteristics of the material have arisen in the development of an engine component as complex as a fan blade. Highlighted in particular are points which arise from; the boundary conditions of the blade geometry imposed by aerodynamic considerations; the directional strength characteristics of the structure arising from its layered composite assembly; and the environmental and stress conditions to which the blades will be exposed in airline service. The planes of weakness at joints and interfaces have had to be clearly identified and their effect quantified for conditions of steady and vibratory stresses and also for the case of severe impulse loading normal to the plane of reinforcement.