Availability Analysis of 3-State Systems

This paper introduces the concept of a pending-failure state in order to consider usual operating and wearout periods of engineering systems and proposes a 3-state system model. System reliability is evaluated in terms of mean time-to-failure (MTTF) and the ratio of ``transition rate from pending failure to failed´´ to ``that from good to pending failure state´´. The analysis is rather general and applies to many systems, regardless of mean duration of pending-failure state. The reliability and availability of this system are higher than a 2-state system model having same MTTF and repair rate.