Operational reliability assessment of an aircraft environmental control system

The aircraft environmental control system (ECS) is composed of several non-identical and non-dedicated subsystems working as warm–cold standby subsystems. Also, their state transition times are arbitrary distributed. This paper presents a flow-graph-based method to calculate time-to-failure data and failure probability of the ECS. The obtained data from the model may be used for maintenance optimization that employs the failure limit strategy for ECS. The model incorporates detectable failures such as hardware failures, critical human errors, common-cause failures, maintenance categories, and switch activation methods. A numerical example is also presented to demonstrate the application of the model.