The Reliability Block Diagram is a graphical methodology to describe a system in an intuitive way to represent the schematics of a system decomposing it into various sub-systems, components or functions. The RBD is build such that the blocks are interconnected accordingly to their relationship and the effect of their failure to the whole system. They are mainly used in reliability engineering and risk analysis for engineering applications to analyze failure events over a system, reduce risk and improve reliability, for example in aerospace and chemical industry; electronics, computation and network design, power plants, etc. An RBD is a Boolean representation for the reliability of a system and equivalent for a Fault Tree Analysis.
In an RBD once the reliability of each component present in system has been related to a corresponding probability distribution model, it is possible to calculate the reliability and other analysis of the whole system at a given certain time. This characteristic helps to identify critical components and model the effect of item failures in different configurations, allowing to decide which arrangement of elements has the best reliability and availability for operational functions.