Fault tree analysis of phased mission systems with repairable and non-repairable components

Methods are developed for correct modeling and quantification of phased mission systems in which the system logic changes during a mission. No manual elimination of minimal cut sets is needed when using common fault tree codes and techniques in this refined reliability analysis with non-repairable components. Another major contribution is the fault tree technique for systems with repairable components. Exact results and rare-event approximations are illustrated for typical systems. The unavailability, the failure intensity, the expected number of system failures and reliability bounds are obtained. General formulas are presented for possible discontinuities at phase boundaries. Components can have dedicated active or standby spares. Common cause failures and tolerated repair times (grace-periods) can be included. Finally, the phases can have deterministic (pre-determined) or random durations.