Mean time to first failure of repairable systems with one cold spare

A general (nonMarkov) 1-out-of-2:G system with statistically-identical components, repair, and cold standby is reviewed. Coverage is considered, viz, failures of the switching mechanism for activating the spare. The explicit derivation of the mean time-to-first-failure and its in-depth discussion appear to be new. The state transition graph and the Petri net both show the way to general (n-1)-out-of-n:G systems of this category. However, for n>2, results are given only for statistically-identical components which are all as good as new, when a repaired component is put to use. This limits applicability of results to electronic systems.