Concept Development for Maintenance Cost Estimation for New Aircraft Systems

Abstract

Aviation industry, along with its greenhouse gas emissions, is expected to grow in the upcoming decades, requiring a substantial reduction in the environmental impact of air transport. Current research is investigating alternative energy carriers, such as hydrogen, together with increasing levels of electrification of both propulsive and secondary power systems. The introduction of these innovative technologies is accompanied by economic uncertainties. Since operating costs constitute a major portion of the total Life Cycle Cost (LCC), and maintenance is one of the largest contributors to operating costs, the capability to estimate maintenance expenditures is essential. Cost assessments are especially important during the early design phases, where design flexibility is highest and multiple configurations can still be evaluated. While maintenance cost estimation methods are available for conventional aircraft, studies addressing hybrid-electric and hydrogen-powered concepts remain limited. Thus, the aim of this thesis is to develop a maintenance cost estimation method ology sensitive to different novel aircraft propulsion technologies and suitable for application during the conceptual design phase, when only high-level aircraft information is available. To achieve this, four short-to-medium-range concepts developed within Deutsches Zentrum für Luft- und Raumfahrt (DLR) are used as case studies. One of the aircraft serves as the reference configuration and employs conventional aircraft systems. The remaining three concepts incorporate novel technologies, including different degrees of hybridization, Liquid Hydrogen (LH2) fuel systems, and Proton Exchange Membrane Fuel Cell Systems (PEMFCSs) replacing conventional Auxiliary Power Units (APUs). The expected maintenance activity is obtained by developing a maintenance plan for each case study and simulating its implementation through a discrete-event simulation. Maintenance plans for the novel concepts are derived by identifying the expected differences relative to the reference aircraft. A Maintenance Planning Document (MPD) analysis is used to estimate the maintenance implications of changes in propulsion architecture. Maintenance activities associated with the novel technologies are derived from a Maintenance Steering Group-3 (MSG-3) analysis conducted by DLR, and complemented with information available in the literature. The simulation results provide a maintenance cost database. The latter is subsequently analyzed to identify the principal maintenance cost drivers, maintaining a level of detail compatible with conceptual aircraft design. A regression analysis is then used to derive Cost Estimating Relationships (CERs) for the individual maintenance cost components. The combination of these CERs forms the proposed maintenance cost estimation method. The developed methodology provides both a maintenance cost assessment for aircraft concepts incorporating hybrid-electric and hydrogen-based technologies, and a maintenance cost model suitable for early-stage aircraft design studies. The results demonstrate the influence of propulsion architecture, LH2 systems, and battery replacement requirements on overall maintenance costs and establish a foundation for future maintenance cost assessments of advanced aircraft concepts.