The main objective of System Engineering is the successful development of complex system. It is based on the application of iterative and recursive processes on each phase or step of the system development. One critical process is the requirement management, particularly when it deals with the safety requirements. These one are non-functional requirements and are related to emergent properties, which come from the integration of the different system components. They must be identified as soon as possible, because they are guards to validate or not the system, which can require changes in system architecture. Moreover, they are formulated at system level and need to be derived at subsystem level. The objective of this paper is to propose a safety management method based on well-known safety methods, in order to organize the different tasks to make the system safe. The method focuses mainly on the definition of the system safety requirements following risk and hazard analysis, and also on their derivation according to a top-down approach. It is based on the well-known Failure Mode, Effects, and Criticality Analysis (FMECA) and the use of Fault Trees and Event Trees.