This paper addresses the general issue of software tool support for designers, helping them to structure, to communicate and to document activities of generation, evaluation and decision. Here the focus is on detailed consideration of desired and undesired behavioural relationships among elements of complex design artefacts and with end users. This is an area that has recently been under discussion by proponents and critics of Affordance Based Design methods. Our solution approach is to extend an existing graph based software tool for design rationale capture that has been in widespread use in an international aerospace company for several years. We are integrating its Issue Based Information System (IBIS) based design argumentation with hierarchical Functional Analysis Diagrams (FAD), a form of Concept Map. The resulting software is being tested by practical application on pilot projects in the company, and initial experiences have been very favourable. The new graph element types, bidirectional relationship types between graphs, and supporting navigational facilities are described. Their use is illustrated by example of an integrated hierarchical FAD and assembly geometry model of a gas turbine engine.@en