Reduction in weight is an important factor with respect to turbine engines used in aircraft. Blades (20) used in such turbine engines may fragment such that it is necessary that the containment casing (42) can resist such fragmentation. Root portions of blades are generally less deformable and therefore require conventionally more robust containment casings. Use of super plastically formed blades allows provision of slots (4, 14, 24, 46) in the root portion which facilitate fragmentation and deformation by the root portion under impact reducing the necessity for greater reinforcement of the containment casing. The slots (4, 14, 24, 24, 46) are created in a membrane utilised for web reinforcement of the blade rather than through intrusive drilling and cutting processes which may introduce machining stresses into their creation and potential tool loss within the high value blade. Additionally, by providing such slots (4, 14, 24, 46) it will be appreciated that the cavity formed within the blade may be sealed without additional machining or other processes.