Optimal maintenance decision for line reparable units (LRU) for an aircraft system - a conceptual approach

Maintenance decisions for the repairable units (LRUs) for an aircraft fleet are needs to be considered carefully while phasing out of an aircraft fleet in terms of cost effectiveness and fleet availability. Discard rate and phasing out period for an aircraft are the critical parameters for determining optimum time to stop the maintenance. The remaining economic value of useful life of an aircraft fleet should be taken into consideration by salvaging the LRUs at the end of phasing out. These units can often be utilized for the aircraft staying in operation and this can influence the maintenance strategy for the units and the aircraft fleet. By salvaging units with remaining service life from retired aircraft, the relative stock level of units compared to operational aircraft will increase. This will give an opportunity to modify the maintenance strategy due to the increased number of units in the stock; units are discarded instead of being maintained which is a cost-effective strategy. In this paper a methodology has been suggested to optimize the availability of repairable units at a lowest life cycle cost, in order to decide at which point further maintenance can safely be stopped, and maintenance resources should be discarded. A mathematical formulation has been derived for the discard rate of aircrafts based on failure rate, mission life and remaining life of the aircrafts in the fleet that helps in managing demand rate of the units during the phase out of the aircraft fleet.