Abstract : Reactive real time systems are critical systems. These systems requirements validation and verification (V&V) activities are very important in terms of cost and time. Therefore, methods and tools that can alleviate and efficiently support V&V activities are of great interest for aeronautic domain. Functional testing is the most commonly used technique for these systems requirements V&V. But, testing methods present some limits: exhaustive test data generation is practically impossible because of the size and the complexity of these systems. In this way, controlling testing effort (complexity and cost) is major, but systems quality demands are very huge. Testing effort characterizes as well the tests definition as the diagnosis. In this perspective, we defined two methodologies based on testability analysis concepts and test strategies. The first methodology aims at guiding relevant functional tests definition and facilitating AIRBUS reactive systems SCADE data flow specification coverage analysis during the validation activities. The second methodology proposes methods supporting the verification activities (relevant tests definition for diagnosis and faulty component identification) based on functional testing on AIRBUS Final Assembly Line (FAL).