This paper briefly reviews the state of the art in Fault detection and Isolation (FDI), and describes a test-case for in-flight fault diagnosis. The main concepts are recalled, the links between the approaches are indicated and the most promising methods are highlighted. The nonlinear models of the system, its sensors and actuators are described in the second part of the article, along with fault scenarios. Constraints restrict the approaches that are applicable on the test-case and suggest quantitative indices that can be used to evaluate fault diagnosis strategies in an aeronautical context.