Modelling of maintenance, within discrete event simulation

The concept of maintenance free operating periods (MFOP) requires co-ordination of failure avoidance, failure anticipation and maintenance delay techniques, with the objective of enhancing operational capability in a cost-effective manner. Individual aspects might be modelled mathematically but discrete event simulation is required for an analysis with the necessary fidelity. The ultra reliable aircraft model (URAM) is an aircraft reliability and maintenance discrete event simulation designed to investigate MFOP concepts. Analysis during its development identified several important factors pertaining to maintenance: Allocation and scheduling of resource; maintenance objectives and their operational & time-based over-ride; forward planning of scheduled & prognostics based maintenance; diagnostics, covering both fault visibility & isolation; task prioritisation, based on system structural importance, criticality importance, time & cost. These have been successfully implemented, making URAM an efficient and representative simulation of aircraft reliability, maintenance support and operational tasking. The factors and their implementation in URAM may easily be transferred to discrete event simulation of other complex assets such as ships and railway systems