In recent years software has become a key element of safety critical systems. The use of Safety Critical Software Systems (SCSSs) has been increased in many critical systems such as Nuclear Power Plants (NPPs), radiotherapy, aircrafts, and many medical devices. These systems rely on the use of safety critical software in controlling and monitoring critical devices. SCSSs are developed in accordance with a set of guidelines and standards produced by the industry, or imposed by a regulator. Despite of the vital role of SCSSs in saving human life, the environment, and properties, there is no generic methodology for developing such systems based on standards and guidelines. This methodology sets an integrated model that concerned about the safety of critical software systems as a component of the critical systems. It consists of the needed processes required for developing SCSSs free of faults. This methodology ensures that SCSSs
are developed using processes based on appropriate standards and guidelines and can be certified accordingly. The objective of this methodology is to produce certified critical software systems that conform to standards and guidelines. The methodology consists of three phases (safety planning and requirements phase, safety analysis phase, and design, implementation, and operation phase). This paper is going to focus on design and implementation phase. The insulin
pump system is applied as a case study on the design and implementation phase.