A model for mean-time-to-repair and mean-logistics-delay-time at the system level

A method is presented for calculating the operational availability, mean time between failures (MTBF), mean time to repair (MTTR), and mean logistic delay time (MLDT) of a system, given the MTBF, MTTR, and MLDT of the lowest replaceable units (LRUs). The method is applicable to systems that undergo operating and nonoperating periods for an indefinite time. Development of the method required extension of the definitions of MTTR and MLDT at the LRU level to the system level. The method of calculating the system level parameters used a model to calculate inherent ability as an intermediate step. An example is presented that demonstrated a computer program suitable for use by a RAM engineer on design and development projects