Operation phase corresponds to the last phase of an industrial project. It has to produce in quantity, quality and also in a limited time delay. To provide better answers to exploitation orders, the operator must be in possession of every information to check the system. But nowadays, automatized systems are often too complex for users and they cannot operate as well as necessary. The major aspect of the problem consists on operations modes. Operations modes are necessary to introduce or modify orders in the production phase, take into account stops, failures and also restarts. Then, the study of running and stop modes must occur in the specification phase, and tools to aid the operator must be developed. This paper presents the MESAP model (Modèle d’Exploitation des Systèmes Automatisés de Production) and its implementation by the HOOD method.