In recent years increasingly pressure has been applied on aircraft component suppliers to reduce design lead-time and design cost of aircraft components. To achieve this reduction in lead-time and cost, advanced automation tools that automate part of the engineering process can be used. Knowledge based engineering (KBE) tools are one such automation tool type and automate part of the engineering process based on existing knowledge within a company. In this paper the development process and use of a KBE application to design machined ribs in an industrial setting is discussed. The development of the KBE tool has resulted in the standardisation of the design methodology. Furthermore it has reduced machined rib design lead-time in a project to develop a bussines jet empennage by 40%.