Abstract Political and socio-economic increasingly-stringent restrictions have led the armed forces of democratic countries to become more aware of how their financial budgets are spent. One major expenditure for military authorities is upon aero-engine maintanence because in-service worsening performance of any mechanical device, such as an aircraft's gas-turbine engine, is inevitable. Each deterioration also shortens the reliable operational life of the engine, thereby resulting in a higher life-cycle cost (LCC). For a military aircraft's mission-profiles, the consequences of an aero-engine's deterioration upon the aircraft's operational-effectiveness, its fuel consumption and life have been predicted, in this project, using validated computer-simulations. These help in making wiser management-decisions, so leading to the achievement of improved engine-utilization, lower overall life-cycle costs and greater mission effectiveness for squadrons of aircraft.