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System safety analysis as decision making tool for aircraft systems

Market or customer requirements, cost, current products' specifications and the other criteria are being considered while designing an aircraft or subsystem. Safety consideration starts from beginning of the design phase and finishes at the end of the aircraft realization. After all safety assessment processes various requirements are generated and these requirements make product safer. In the aircraft design process, one has to comply with the quantitative requirements which arise from Regulation FAR 25.1309 (equipment, systems and installations) of aircraft certification documents. ARP 4761 Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment is recommended for safety assessment by SAE International. The most common methods used in quantitative analysis are Fault Tree Analysis (FTA), Markov Analysis (MA) and Dependence Diagrams (DD). Fault tree analysis method is the most common. The system safety assessment is offered not only during design phase consideration but also can be used for system selection criteria of aircraft sub systems in the early stage of conceptual design. Two different aircraft equipment with similar function are compared using fault tree analysis as an example by this paper. Aim is to use safety fault tree analysis for trade-off studies. Finally, this paper opens a discussion about the role of safety analyses of an aircraft system selection.