Systems often are an integration of subsystems. Sub-systems are integrated together through a specific functional structure.
A Fault Tree is a representation of such functional integrated structure of sub-systems. A failure in a sub-system can potentially lead to the failure of the entire system. A fault tree will evaluate areas of high risk in failures and help you calculate the probabilities of system failure based on the probabilities of sub-system failure.
An Event Tree models sequential-event led failures in systems. Each node in the Event tree logs the possibility of the event occurring. Based on complex chains of sequenced failures, high risk events are highlighted. Adding redundancies and reducing probability of critical events will help bringing down the Failure rate in a significant manner.
