Towards climate-neutral aviation: Assessment of maintenance requirements for airborne hydrogen storage and distribution systems

Airlines are faced with the challenge of reducing their environmental footprint in an effort to push for climate-neutral initiatives that comply with international regulations. In the past, the aviation industry has followed the approach of incremental improvement of fuel efficiency while simultaneously experiencing significant growth in annual air traffic. With the increase in air traffic negating any reduction in Greenhouse Gas (GHG) emissions, more disruptive technologies such as hydrogen-based onboard power generation are required to reduce the environmental impact of airline operations. However, despite initial euphoria and first conceptual studies for hydrogen-powered aircraft several decades ago, there still has been no mass adoption to this day. Besides the challenges of a suitable ground infrastructure, this can partly be attributed to uncertainties with the associated maintenance requirements and the expected operating costs to demonstrate the economic viability of this technology. With this study, we address this knowledge gap by estimating changes towards scheduled maintenance activities for an airborne hydrogen storage and distribution system. In particular, we develop a detailed system design for a hydrogen-powered, fuel-cell-based auxiliary power generation and perform a comparative analysis with an Airbus A320 legacy system. That analysis allows us to (a) identify changes for the expected maintenance effort to enhance subsequent techno-economic assessments, (b) identify implications of specific design assumptions with corresponding maintenance activities while ensuring regulatory compliance and (c) describe the impact on the resulting task execution. The thoroughly examined interactions between system design and subsequent maintenance requirements of this study can support practitioners in the development of prospective hydrogen-powered aircraft. In particular, it allows the inclusion of maintenance implications in early design stages of corresponding system architectures. Furthermore, since the presented methodology is transferable to different design solutions, it provides a blueprint for alternative operating concepts such as the complete substitution of kerosene by hydrogen to power the main engines

Hybrid Electric Propulsion Systems for Medium-Range Aircraft from a Maintenance Point of View

The use of a hybrid electric propulsion system for aircraft offers the potential to increase aircraft efficiency, reduce fuel consumption and thus reduce emissions. Design concepts, emission analysis and aircraft performance are being studied extensively. However, how future hybrid electric propulsion systems will change the maintenance, repair and overhaul (MRO) of an aircraft is also an important consideration. This paper examines the effects of hybridisation on a parallel hybrid electric propulsion system of a medium-range aircraft, the Airbus A320, powered by an IAE V2500 engine. The electric motor is powered by a battery and is used to assist the turbofan engine, mainly during the takeoff phase. The additional system components of the chosen hybrid electric propulsion system and their corresponding damage mechanisms are addressed from a maintenance point of view. Challenges for future maintenance are discussed and possible failure modes and failure possibilities are analysed. For this purpose, a Failure Mode and Effects Analysis and a Fault Tree Analysis will be carried out. The results of this analysis can be used to determine how the additional components need to be designed to maintain the overall safety of the propulsion system at the current level. This will also provide needs and ideas for a future design for maintenance

Can Urban Air Mobility become reality? Opportunities, challenges and selected research results

Urban Air Mobility (UAM) is a new air transportation system for passengers and cargo in urban environments, enabled by new technologies and integrated into multimodal transportation systems. The vision of UAM comprises the mass use in urban and suburban environments, complementing existing transportation systems and contributing to the decarbonization of the transport sector. Initial attempts to create a market for urban air transportation in the last century failed due to lack of profitability and community acceptance. Technological advances in numerous fields over the past few decades have led to a renewed interest in urban air transportation. UAM is expected to benefit users and to also have a positive impact on the economy by creating new markets and employment opportunities for manufacturing and operation of UAM vehicles and the construction of related ground infrastructure. However, there are also concerns about noise, safety and security, privacy and environmental impacts. Therefore, the UAM system needs to be designed carefully to become safe, affordable, accessible, environmentally friendly, economically viable and thus sustainable. This paper provides an overview of selected key research topics related to UAM and how the German Aerospace Center (DLR) contributed to this research in the project "HorizonUAM - Urban Air Mobility Research at the German Aerospace Center (DLR)". Selected research results that support the realization of the UAM vision are briefly presented.Comment: 20 pages, 7 figures, project HorizonUA

A Collaborative Systems of Systems Simulation of Urban Air Mobility: Architecture Process and Demonstration of Capabilities

Urban Air Mobility (UAM) presents a complex challenge in aviation due to the high degree of innovation required across multiple domains to realize it. From the use of advanced aircraft powered by new technologies, the management of the urban air space to enable high density operations, to the operation of specialized vertidromes serving as a start and end point of the vehicles, the UAM paradigm necessitates a significant departure from aviation as we know it today. In order to understand and assess the many facets of this new paradigm, a Collaborative Agent-Based Simulation is developed to holistically evaluate the system through the modelling of the stakeholders. In this regard, models of vertidrome air-side operations, urban air space management, passenger demand estimation and mode choice, vehicle operator cost and revenues, vehicle maintenance, vehicle allocation, fleet management based on vehicle design performance and mission planning are brought together into a single Collaborative System of Systems Agent-Based Simulation of Urban Air Mobility. Through collaboration, higher fidelity models of each domain can be brought together into a single environment which can then be exploited by all partners, achieving comprehensiveness and fidelity levels not achievable by a single partner. Furthermore, the integration enables the capture of cross-domain effects with ease and allows the domain-specific studies to be evaluated at a holistic level. Agent-Based Simulations were chosen for this collaborative effort as it presents a suitable platform for the modelling of the stakeholders and interactions in accordance with the envisioned concept of operations. This work presents the capabilities of the developed Collaborative System of Systems Agent-based Simulation, the development process and finally a visual demonstration. The objectives of this presentation are: • Detail the development process of the Collaborative System of Systems Agent-Based Simulation • Demonstrate a holistic simulation of UAM built through collaboration of multiple tools/modules such as vertiport and trajectorie

Scientific Assessment for Urban Air Mobility (UAM)

Better connecting the international research community and the International Civil Aviation Organization (ICAO) enables effective assessments of novel aviation innovations. The International Forum for Aviation Research (IFAR) created a group on Urban Air Mobility (UAM) to explore the broad array of aspects relevant to the ICAO mandate. The assessment began with a study of the current industry landscape, including an overview of existing market studies, proposed aircraft designs and concepts, and potential paths of industry evolution. The Industry Assessment is summarized into key takeaways highlighting the need for international assessments on economic and societal factors associated with UAM, common understanding of the extent to which the nascent industry can leverage current infrastructure and regulatory structures, and harmonization of industrywide terminology. The subsequent Scientific Assessment, developed through cooperative efforts between international domain experts, captures 17 focus areas relevant to UAM. All focus areas present opportunities for further research. Key takeaways include: the need for further study of the impact of autonomous systems (AS) on the industry; infrastructure requirements (including vertiports and weather sensing) to support the industry; and data requirements (including domains such as cybersecurity, emissions, and safety) to ensure safe, scalable operations. Finally, a brief overview of the current standards landscape as relevant to the Scientific Assessment is presented, which displays the benefits of applying digital systems engineering techniques to map current research efforts to ongoing standards activities

Identifying Maintenance Tasks for Aircraft Hydrogen Systems using the MSG-3 Analysis and their Implications on Operation

Aviation faces political and social pressure to reduce its climate impact. Fuelling air-craft with green hydrogen (H2) is one approach to reduce the lifecycle emissions. Airbus announcement to develop a hydrogen powered aircraft by 2035, increased the chance for hydrogen to become the next leap in civil aviation (Spaeth 2020). Hydro-gen research in aviation mainly focuses on the development and comparison of dif-ferent aircraft designs. However, maintenance for hydrogen powered aircraft is wide-ly disregarded by researcher and if mentioned, only marginally. This gap within the existing literature is addressed with our presentation, in which we present the application of the MSG-3 analysis on a real H2 aircraft system within the scope of the research project “Hydrogen Aviation Lab”. A simple H2 system, that could replace an auxiliary power unit (APU), is developed for the integration into a phased-out Airbus A320. The system’s main components consist of the tank for liq-uid H2, a fuel cell as consumer for gaseous H2 and the connecting piping. Our goal is to identify the maintenance tasks for that novel system based on the detailed sys-tem layout and their consequences on the aircraft operation under the assumption, that the H2 system replaces the APU of the aircraft. To identify the maintenance tasks and with the detailed H2 system design, we con-duct the steps of the MSG-3 analysis in the first part of the study. The H2 system is divided into subsystems, and their functions and functional failures are systematically identified. Based on the failure effects and the components technical specifications, maintenance tasks and intervals are determined. The maintenance man hours for the tasks are identified subsequently. The individual tasks are combined, so that schedule for the H2 system is conducted

Towards Minimum Expenditure MRO Concepts for UAM trough Vehicle Design and Operational Modelling

Well-established aviation companies, start-ups, and governmental institutions aim to lift Urban Air Mobility (UAM) into the skies. The novel aircraft architecture combined with on-demand operations servicing a small network means a significant change in its operation and maintenance requirements compared to commercial airlines. On-demand flights exhibit non-deterministic behaviour meaning that future flight missions and related variables such as the aircraft position and Flight Hours (FHs) are unknown. Consequently, existing methods to optimise aircraft assignment and maintenance planning cannot be transferred directly from traditional airlines. This study attempts to picture and understand the behaviour of an aircraft fleet in an on-demand UAM transport system regarding the interlinking between operation and maintenance. Hereby, the most significant parameters will be identified and the optimum within the system’s limitations will be determined. In order to address this, a transport and maintenance simulation is introduced, in which aircraft are modelled as agents and service flight missions within a simple network. As soon as hard time maintenance intervals, limited by FHs or flight cycles, are fully utilized, aircraft transfer to a maintenance base. As maintenance bases have a limited capacity for simultaneous checks, vehicles compete with each other for that limited resource, which can cause waiting times. To understand the impact on the whole technical operational ecosystem, the maintenance costs are extended to include running costs of the maintenance bases and opportunity costs for times aircraft cannot generate revenue, such as waiting time for a check. The most important output parameters to evaluate the quality of the simulation are the maintenance costs and the network transport capacity. Opportunity costs are identified as cost driver and primarily depend on the waiting time for maintenance checks. With changes in the operation of aircraft, the waiting time can be influenced. Two simple approaches to decrease the fleet waiting time and thereby reduce the maintenance costs are presented. One option is to trade a certain percentage of the vehicle’s remaining useful lifetime for earlier checks to avoid waiting times. With the other option, the way how aircraft are assigned to missions is altered. Both approaches can reduce bottlenecks at the maintenance bases. The system’s optimum combines both approaches and results in a good interlocking, with maintenance costs in the range of approx. $ 60/FH. About two-thirds of the maintenance costs account for the actual labour and material costs during the checks, the remaining third is the sum of the opportunity costs and the running expenses

Identifying challenges in maintenance planning for on-demand UAM fleets using agent-based simulations

The novel aircraft architectures for Urban Air Mobility (UAM), combined with pure on-demand operations, mean a significant change in aircraft operation and maintenance compared to traditional airliners. Future flight missions and related variables such as the aircraft position or utilisation are unknown for on-demand operation. Consequently, existing methods to optimise aircraft assignment and maintenance planning cannot be transferred. This study examines the behaviour of an aircraft fleet in an on-demand UAM transport system regarding the interlinking between operation and maintenance. Initially, a potential maintenance schedule for UAM vehicles is deduced. A transport and maintenance simulation is introduced where aircraft are modelled as agents servicing a simple network. As aircraft reach their maintenance intervals, they transfer to one of the maintenance bases and compete for that resource. Since that competition can result in avoidable waiting times, the maintenance costs are extended by running costs for the bases and opportunity costs for missed revenue during these waiting periods. Opportunity costs are cost drivers. To reduce the waiting times, two operational approaches are examined: Extending the opening hours of the maintenance facilities and checking the aircraft earlier to reduce simultaneous maintenance demand. While an extension of operating hours reduces the overall maintenance costs, the adjustment of tasks is more effective to lower waiting times. Thus, an improved system needs to use a combined approach. That combination results in overall maintenance costs of approximately $ 58 per flight hour of which about seven percent account for the opportunity costs

Heuristic Approach for Aircraft Assignment and Maintenance Scheduling of On-demand Urban Air Mobility Vehicles

The development vehicles and concepts for Urban Air Mobility (UAM) has been encouraged the technology enhancements such as the introduction of the 5G standard for mobile networks or continuous improvements in battery performance. While past research efforts have covered social acceptance of airborne vehicles in urban areas, autonomous piloting, their integration into airspace and the development of the aircraft themselves, maintenance and scheduling aspects have hardly been considered thus far. Simultaneously, the nature of on-demand operation for Urban Air Mobility Vehicles (UAMVs) differs from traditional airline operations as future utilization and aircraft positions are only known a few minutes in advance. As a consequence, established concepts, known as Aircraft Maintenance Routing Problems (AMRPs) that harmonize the routing of airliners with maintenance activities, cannot be applied to the maintenance scheduling of UAMVs. Within this study, a heuristic approach is presented to assign aircraft to flight missions under consideration of their imminent maintenance needs. The key principle of this assignment strategy is the use of a weighted bidding model that incorporates aspects of dead head flight, as well as avoidable waiting times for the completion of maintenance tasks. Ultimately, this approach will reduce conflicting situations for limited maintenance capacities for flight-hour-driven scheduled maintenance checks. The heuristic is implemented into a discrete events flight simulation, simulating 160 UAMVs in a generic UAM network with two off-grid maintenance facilities with a simulation time span of one year. The result of the proposed heuristic is compared to a baseline scenario in terms of accepted flight request rate, the average waiting time for maintenance completion, the average waiting time before commencement of a mission and the maintenance base utilization. Furthermore, different simulations are run with varying weighting factors for maintenance and operating aspects to examine possible improvements towards the heuristic’s performance. Hereby, the interlinking between operation and maintenance could be improved with the usage of the maintenance scheduling heuristic. As a result, the fleet maintenance waiting time could be reduced by a factor of 2.6 and the share of missed flight requests due to maintenance downtimes could be limited to one percent. Additionally, the utilization of the maintenance bases is also increased through the adapted scheduling and assignment heuristi