The effect of infant mortality of spares on switching system maintenance and downtime

An exact long-term solution and a numerical approximation are presented for the impact of infant mortality of spares on switching system maintenance and downtime. The numerical approximation is used to calculate the initial transient characteristics of the number of replacements, because theoretical results are difficult to get. Results show that the impact of the higher mortality replacement rate of spares on maintenance and downtime can be significant, depending on the steady-state replacement rate of circuit packs within the system. For a hypothetical switching system, it is shown that the effect on maintenance can range from a 0.1 to 30% increase, while the effect on downtime can range from a 0.2 to 70% increase. The authors also propose a preliminary requirement for no more than a 10% increase in maintenance and downtime