This paper describes the structural design of a composite material front housing for the T56 turboprop reduction gear case.The objective of the composite gear case is demonstration of the feasibility of composites for stiff, lightweight gear reduction cases and the advancement of structural and material technology.Turboprop reduction gear assemblies have typically used magnesium or aluminum for the case structure. Magnesium has reasonable strength properties and low density but the modulus is also low; furthermore, it exhibits poor corrosion resistance. Aluminum has sufficient strength but the specific stiffness, E/ρ, is similar to magnesium so the case is heavy for many applications. In addition to these disadvantages, the mounting requirements for propellers, engine, and transmissions dictate high loads on the gear case structure.Consideration of these factors indicated the desirablility of case materials stronger than magnesium with no weight penalty and adequate corrosion protection. A review of suitable case materials showed composites offer the major advantages. The selected boron/epoxy exhibits high strength and specific stiffness, lightweight, good corrosion resistance, and suitability for molding.