Green Commercial Aviation Supply Chain—A European Path to Environmental Sustainability

The last century has witnessed European commercial aviation flourishing at the cost of environmental degradation by boosting greenhouse gas and CO2 emissions in the atmosphere. However, the outcry for net-zero emissions compels the sector's supply chain to a minimum 55% reduction of greenhouse gas emissions below the 1990 level by 2030 and zero CO2 emissions by 2050. This study examines a European environmental sustainability path toward a green commercial aviation supply chain. Driven by literature and a review of related documents, two propositions were advanced to orient perspectives on the relationship between pollution and the commercial aviation supply chain and actions being taken toward environmental sustainability. In semi-structured interviews, seventeen aerospace associates endorsed pollution sources in the commercial aviation supply chain during the four stages of the aircraft life cycle, including extracting the raw materials, manufacturing, ground and flight operations, and end-of-service. They recommended transitioning into green commercial aviation through the widespread deployment of innovative technologies, from modifying airframes to changing aviation fuel, utilizing alternative propulsion systems, adopting circular manufacturing, and improving air traffic management.

FÍLYOS LÍMANI AÇISINDAN KARADENÍZ'DE HÍZMET VEREN RÖMORKÖRLERÍN SEVK SÍSTEMLERÍ ÜZERÍNE BÍR DEĞERLENDÍRME

En önemli taşımacılık sektörlerinden biri olan denizyolu taşımacılığında meydana gelen artış, doğal olarak yeni liman sahalarının kurulumuna yol açmaktadır. Son 10 yıllık süreçte, Türkiye'nin farklı bölgelerinde kurulu olan birçok liman, özellikle korona virüs pandemisinde, değerli malların taşınmasında tonaj bazında daha büyük paya sahip olan denizyolu taşımacılığının sürdürülebilirliği ve gelişimi için etkin rol almıştır. Karadeniz Bölgesinde kılavuzluk, römorkaj ve palamar hizmetleri, atık ve çöplerin tahliyesi, tatlı su ve elektrik tedariği sağlayan birkaç liman bulunmaktadır. Filyos Limanı ise fiziki ve konumsal avantajları ile birçok alanda liman hizmeti verebilecek ve bölgenin artan taşımacılık ihtiyacının karşılanmasına önemli katkı sağlayacaktır. Ayrıca son yıllarda bölgede keşfedilen doğalgaz rezervleri de limanın potansiyel ve önemini arttırmaktadır. Bu çalışmada Karadeniz Bölgesinde bulunan limanlar, boyutsal özellikleri ve verilen liman hizmetleri, özellikle römorkörlerle gerçekleşenler temel alınarak ifade edilmektedir. Küresel çevre algısı, deniz taşıtlarında sürdürebilirlik ve verimlilik, ulusal ve uluslararası düzenlemeler ve son yıllarda inşa edilen römorkörler dikkate alınarak, bu liman sahasında ileride hizmet verecek römorkörlerin sevk sistemleri hakkında değerlendirmeler yapılmaktadır.Alternate abstract:Growth in maritime transport, which is one of the most vital transportation sectors, naturally leads to establishment of new port areas. In last decade, many ports established in different regions of Turkey have taken an active role in sustainability and development of maritime transport, which has a larger share in the transportation of valuable goods on basis of tonnage, especially during coronavirus pandemic. Several ports in the Black Sea Region provide pilotage, tugboat and mooring services, discharge of waste and garbage, supply of fresh water and electricity. Filyos Port, moreover, will be able to provide port services in many areas with its physical and locational advantages and will make a significant contribution to meeting increasing transportation needs. Furthermore, natural gas reserves discovered in the region in recent years increase potential and importance of port. In this paper, ports in the Black Sea Region, dimensional features and provided port services are expressed on the basis of tugboats. Considering the global environmental perception, sustainability and efficiency in sea vehicles, national and international regulations and tugboats built in recent years, evaluations are made about the propulsion systems of tugboats that will serve in this port area in the future.

Future Vehicles May Arrive Soon [Automotive Electronics]

After the two last virtual conferences in 2019 and 2020 run by Prof. Pablo Arboleya from the University of Oviedo (Spain), the IEEE Vehicle Power and Propulsion Conference (VPPC) was held for the first time in Merced, California, USA, last November. The conference was organized by a very motivated team from the University of California, Merced, led by Prof. Ricardo De Castro. With the motto 'connect green e-motion' worldwide in a complete network, the four-day conference delivered insight and intelligence from several key players at the forefront of hybrid and electric vehicle (EV) development. A very attractive program was prepared, including four outstanding keynote speeches, three tutorial lectures, and the in person or virtual presentation of 143 papers. During the last conference day, attendees had the opportunity to visit two technical sites: TRC California and the University of California, Berkeley. VPPC 2022 was the first VPPC after the COVID-19 lockdowns and was run in hybrid mode, with in-person and online attendees. VPPC 2022 continues to be the venue for researchers, educators, and engineers to share the latest results in research, teaching, and development of EV and hybrid vehicles and related technologies, as shown in Figure 1. It was an important forum where the academic and industrial communities and policymakers discussed new technology trends and collaboration for mutual development at a crucial time just before the 2022 United Nations Climate Change Conference. © 2005-2012 IEEE.

Environmental impact assessment of a newly developed solid oxide fuel cell-based system combined with propulsion engine using various fuel blends for cleaner operations

After the COVID-19 pandemic has spread throughout the world, many research institutions and industrial organizations are putting great efforts into producing environmentally friendly solutions for the transportation sector. This paper presents a newly developed combined solid oxide fuel cell system with a turbofan engine that can use five alternative fuels, such as dimethyl ether, methanol, hydrogen, methane, and ethanol, with different blending ratios to form five fuel blends. The proposed system is studied in this paper using exergoenvironmental analysis (which is known as environmental impact assessment by exergy) in order to quantify and evaluate the environmental impact. The combined turbofan has an exergetic efficiency of 82%, with total fuel and product exergy rates of 905 and 743 MW, respectively. The total environmental impact caused by emissions and exergy destructions has a range of 4000 to 9000 Pt/h for all the fuel blends. The specific exergoenvironmental impact values of electricity production vary from about 3 to 8 mPt/MJ for solid oxide fuel cells and 10 to 25 mPt/MJ for the three turbines. The exergoenvironmental impact of the thrust force is a minimum of 34 Pt/(h.kN) for the RF1 fuel and a maximum of 87 Pt/(h.kN) for the RF4 fuel. © 2022

Systematic Overview of Newly Available Technologies in the Green Maritime Sector

The application of newly available technologies in the green maritime sector is difficult due to conflicting requirements and the inter-relation of different ecological, technological and economical parameters. The governments incentivize radical reductions in harmful emissions as an overall priority. If the politics do not change, the continuous implementation of stricter government regulations for reducing emissions will eventually result in the mandatory use of, what we currently consider, alternative fuels. Immediate application of radically different strategies would significantly increase the economic costs of maritime transport, thus jeopardizing its greatest benefit: the transport of massive quantities of freight at the lowest cost. Increased maritime transport costs would immediately disrupt the global economy, as seen recently during the COVID-19 pandemic. For this reason, the industry has shifted towards a gradual decrease in emissions through the implementation of "better" transitional solutions until alternative fuels eventually become low-cost fuels. Since this topic is very broad and interdisciplinary, our systematic overview gives insight into the state-of-the-art available technologies in green maritime transport with a focus on the following subjects: (i) alternative fuels;(ii) hybrid propulsion systems and hydrogen technologies;(iii) the benefits of digitalization in the maritime sector aimed at increasing vessel efficiency;(iv) hull drag reduction technologies;and (v) carbon capture technologies. This paper outlines the challenges, advantages and disadvantages of their implementation. The results of this analysis elucidate the current technologies' readiness levels and their expected development over the coming years.

Environmental impact assessment of a newly developed solid oxide fuel cell-based system combined with propulsion engine using various fuel blends for cleaner operations

After the COVID-19 pandemic has spread throughout the world, many research institutions and industrial organizations are putting great efforts into producing environmentally friendly solutions for the transportation sector. This paper presents a newly developed combined solid oxide fuel cell with a turbofan engine that can use five alternative fuels, such as dimethyl ether, methanol, hydrogen, methane, and ethanol, with different blending ratios to form five fuel blends. The proposed system is studied in this paper using exergoenvironmental analysis (which is known as environmental impact assessment by exergy) in order to quantify and evaluate the environmental impact. The combined turbofan has an exergetic efficiency of 82%, with total fuel and product exergy rates of 905 and 743 MW, respectively. The total environmental impact due to emissions and exergy destruction has a range of 4000 to 9000 Pt/h for all the fuel blends. The specific exergoenvironmental impact values of electricity production vary from about 3 to 8 mPt/MJ for solid oxide fuel cells and 10 to 25 mPt/MJ for three turbines. The exergoenvironmental impact of thrust force is a minimum of 34 Pt/(h.kN) for RF1 and a maximum of 87 Pt/(h.kN) for RF4.

Second-Year Review of the NSF-DoD REU Site: HYPER

The challenges associated with achieving hypersonic flight, developing advanced propulsion systems, and designing reusable launch platforms are strongly interdisciplinary. Exposing undergraduate students to interdisciplinary research is recognized as a means to equip society's future engineers and scientists with the broad skillset necessary to contribute to these areas. The jointly funded NSF-DoD REU site Advanced Technologies for Hypersonic Propulsive, Energetic and Reusable Platforms (HYPER) unites multidisciplinary interests to study advanced structures and systems with application to hypersonics, space, propulsion, and energy. Over the course of two 10-week summer sessions (2019 and 2021), participants have gained hands-on training in contemporary challenges such as: (1) utilizing advanced manufacturing techniques for high-value components, (2) integrating in situ monitoring of stress-strain evolution, (3) developing novel methods for improved internal cooling and heat transfer effectiveness, (4) mitigating flutter through advanced rotor dynamic control, etc. Eleven research projects have been crafted to engage students in PhD-level topics. Many of these challenges rely on approaches that cut across disciplines and research techniques (e.g., experiments and computer simulation). The present reporting serves as a synopsis of challenges, advances, and lessons learned conducting the research thus far. The site HYPER has six core objectives that relate to: (1) preparing students for graduate school and/or research-oriented careers, (2) fostering technical skills in student participants, (3) improving participants' communication skills, (4) marketing to and recruiting a diverse group of participants, and more. Assessment of the program outcomes according to these objectives are reported here with data gathered after two years. Program outcomes were conducted with an external evaluator affiliated within the University of Central Florida's Program Evaluation and Educational Research Group (PEER). Results demonstrate a very effective site with strongly positive outcomes for all participants. Insights are provided so this research effort may be confirmed by other independent sites. It should be noted that the 2020 session was postponed out of an abundance of caution based on the uncertain and evolving conditions facilitated by the COVID-19 pandemic. © American Society for Engineering Education, 2022.

Considerations About Algorithmic Literacy

In recent years, digital media is becoming increasingly popular as a source of health information. The widespread use of digital media, such as social media platforms, has become a part of everyday life, especially when it comes to COVID-19-related information. Extensive academic research compounded by general societal discord suggests that the future looks worrisome, especially when people use their mobile phones to seek health-related information. Relying on the environment of digital sources that are often processed by imperfect or biased algorithms augments the risk of being misinformed about COVID-19. This environment propelled the COVID-19 pandemic to explode with new waves of fake news and misinfodemics. The urgent challenge of health communication is to provide timely science-based health information to help people resist misinfodemics. This article explores disinformation and misinfodemics and the extent to which algorithmic literacy can contribute to eHealth literacy and manage societal discord on important medical topics.

Psyche Project Implementation During the COVID Pandemic

In January 2017, 'Psyche: Journey to a Metal World' was selected for implementation as part of NASA's Discovery program. The Psyche mission will utilize electric propulsion with SPT-140 Hall thrusters to rendezvous and orbit the metal-rich asteroid (16) Psyche, in the main asteroid belt between Mars and Jupiter. The Psyche spacecraft requires no chemical propulsion and, when launched in 2022, will be the first mission to use Hall thrusters beyond lunar orbit. The Psyche spacecraft is a hybrid development with Jet Propulsion Laboratory (JPL)-provided deep-space avionics and communications equipment mounted on a high-heritage MAXAR (formerly Space Systems Loral) Solar-Electric Propulsion (SEP) Chassis, based on their 1300 series of GEO communications satellites. The spacecraft is equipped to support a suite of science instruments, as well as a demonstration of the Deep Space Optical Communications (DSOC) technology. The spacecraft has sufficient onboard resources, autonomy, redundancy, and operability to complete a 3.5-year cruise to 16 Psyche, followed by a 20-month campaign of science investigations while orbiting the asteroid. The mission's early concept design and progress through Preliminary Design Review (PDR) has been described in previous work. The paper will cover the recent mission progress from the Critical Design Review (CDR) through the start of Spacecraft Environmental Testing, which took place during the COVID pandemic. The authors will highlight the successful remote collaboration between the major partners: ASU, JPL, MAXAR, and the Payload teams that led to the initiation of the Assembly, Test, Launch, Operations Phase (ATLO) in early March 2021. Emphasis will be placed on the effects that the COVID-19 pandemic had on the work environment over the last 16+ months, including challenges to delivery of flight hardware and test equipment. In addition to the COVID-19 challenges, other significant anomalies discovered during design and test will be described along with any impacts to the overall science capability of the mission. © 2022 IEEE.

Soil Moisture Active Passive: Flying A Spacecraft From Home

During the unprecedented COVID-19 pandemic, the Soil Moisture Active Passive (SMAP) spacecraft was flown almost entirely from the homes of operations personnel. SMAP is a science spacecraft mission, measuring soil moisture, its freeze/thaw state, and other parameters on a global scale to support weather forecasting, disaster response and climate research. Institutional pandemic response protocols at the Jet Propulsion Laboratory (JPL) prescribed that only mission critical and mission essential work may be performed on-site. Fortuitously, automation is a defining characteristic of SMAP operations. Ground systems are used to automate routine tasks but not to replace or replicate the technical expertise of human operators. Nominal operations are repetitive, occur around the clock, and automation allows them to be low cost. Potential contingency scenarios were assessed. Consequences of lost or degraded capability of major mission system elements were evaluated. In particular, the impacts of progressively reduced availability of ground antenna stations were considered. Operational adjustments were made to conduct nearly all functions remotely. Naturally, all meetings were conducted online, and chat rooms were set up. For the infrequent real-time operations, an uplink team of two was deployed to the mission ops center, and all other participants remotely monitored the telemetry and systems. The project policy that all manual uplinks must be performed on-site by two persons was retained. Maneuvers, normally performed on-site with support from several system and sub-system operators, were now performed completely remotely by activating one of a set of pre-loaded maneuver sequences. Despite the situation, significant non-routine activities were accomplished to address anomalies and programmatic needs. A major upgrade of the ground data system was performed, replacing aging hardware and updating obsolete software, although on a longer timeline than originally planned. An innovative parallel operations architecture was used to validate functionality and performance of the upgraded system, while still operating on the legacy system. Similarly, the flight system testbed needed to be upgraded, with the configuration swapped multiple times to accommodate testing and other programmatic needs. The spacecraft experienced a significant corruption of the non-volatile memory. Diagnosis and recovery using new tools were performed almost entirely from home. In summary, SMAP remote operations during the pandemic have been and continue to be highly successful. These experiences have demonstrated that much of the operations may actually be conducted remotely. © 2022 IEEE.

ISABE – 50 Years Revolution….again!

Beyond these commercial successes, there was a host of ideas for supersonic and hypersonic propulsion, NASA’s hydrogen aircraft evaluation, variable cycle aircraft engines, turboramjets and other novel aircraft engine concepts. There are international efforts to continue to deliver affordable air travel, protecting the very widespread benefits of aviation, and bringing solutions that meet the very deep need to mitigate the aviation impact of climate change. Urgent and substantial technology investments are now needed in this moment of crisis (noting that the Greek work κριsις means judgement (and decision) to ensure the protection of the environment and continuing economic growth.

Passive Method for Wax Casting in the Production of the Fuel Grain for in-space Hybrid Rocket

The Space Enabled Research Group at MIT is conducting a multiyear research effort to better understand the technical and logistical challenges posed by the implementation of a wax-based hybrid chemical in-space propulsion system. Paraffin and beeswax are being considered as candidate fuels. The overarching effort includes imagery analysis conducted on paraffin and beeswax centrifugal casting tests conducted onboard progressively higher-fidelity experimental platforms within transparent hardware which aids in optical investigations. Such platforms include a laboratory optical table experiment, as well as a vacuum chamber test, a parabolic trajectory microgravity aircraft (three flights to date), the Blue Origin New Shepard suborbital launch vehicle (three experiments onboard and scheduled for mid to late 2022), and potentially the Destiny laboratory module of the International Space Station. Each of these platforms allows for testing in a new environment or increasingly longer-duration microgravity. The main focus of this paper is in regards to a Suborbital flight experiment. This experimental setup had multiple limiting factors such a size, 10 cm x 10 cm x 20 cm and power of approximately 5 W. This lead to trying a new approach to the spin casting approach used previously by the team, as the method of forming the fuel grain annulus. This new approach was passive, meaning it did not require any additional power other than to melt the wax, and relied heavily on the surface tension properties of the containment chamber. The surface tension of the end caps was modified by using an oleophobic substance to repel the wax. Unfortunately, due to the Covid-19 pandemic, delays on flight caused results to not be ready before the date of publication of this paper. © 2022, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

Comprehensive Assessment of Electric Vehicle Development, Deployment, and Policy Initiatives to Reduce GHG Emissions: Opportunities and Challenges

Embracing innovative vehicle technology in the transportation sector provides constructive solutions to the rising pollution levels and global warming. Developing Electric Vehicles (EV) with market competency, deploying standardized charging infrastructure in sufficient numbers, and government promotional policies all impact EV adoption and help reduce tail pipe emissions. To determine the key hurdles to EV adoption that still exist in today's market, the comparison between the most preferred EV and the Conventionally Propelled Vehicle (CPV) is deliberated under various parameters like vehicle class, type, specification, performance, pricing etc. The research assessed the countries with the most CPV (China, the USA, Japan, Germany, and India), as well as the expertise and experience of the country (Norway) that pioneered the EV industry, to discover the key policies that will help accelerate EV adoption in their respective regions. Significant findings within the local market and across markets belonging to the countries of concern and research recommendations addressing the issues have been discussed as a result of the study conducted with data obtained from the vehicle manufacturer's website, government statistical institutes, and other affiliated survey organizations, as well as technical reports published online. These qualitative and quantitative findings and recommendations will aid in the creation of EV and charging station designs, as well as the formulation of strategies aimed at generating more cost-effective EV designs that take into account local usage patterns, car kinds, and performance. It also assists legislators in their efforts to streamline EV policy. Consideration of these issues aids in the reduction of greenhouse gas (GHG) emissions.

Development of Safety Processes for Design and Manufacture of Small Liquid Propellant Engines and Launch Vehicles

The Cal Poly Pomona (CPP) Liquid Rocket Lab project teams in the 2020-2021 academic year further developed the planning of the engine injector water flow testing, oxygen compatibility and cleaning procedures and further advanced the Mobile Rocket Engine Test Stand piping and structural design. Failure Modes and Effects Analysis were also performed on the system elements to be able to target the critical components for failure mitigation design and procedure development. The CPP revised system for FMEAs is shown. These items were needed to be accomplished in order to perform an engine hot firing for the Bronco 1 Launch Vehicle. This paper describes briefing some the status of the CPP FAR-Mars competition progress and the vehicle systems manufacturing and assembly modifications related to safety developed during our program activity. Some of our testing objectives were postponed due to the COVID19 activity constraints. © 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.

Building a 100% Online Rocket Propulsion Course During a Pandemic

The worldwide COVID pandemic of 2020 forced universities to quickly shift their instructional strategies from the classroom toward online delivery modes to respond to the disruptive social distancing guidelines that evolved. The objective of this paper is to describe the process and the results of rebuilding an undergraduate/graduate rocket propulsion class for a new 100% online deployment due to the COVID pandemic. The case study is Rocket Propulsion I at the University of Alabama in Huntsville for the fall of 2020. A team of instructional designers led a Quality Education Practices Online training program with the instructor to restructure the entire course to meet baseline online distance learning standards. During this rebuild, the instructor also incorporated and developed all new lecture materials, quizzes, and homework based on the adoption of a new course textbook. The comprehensive approach included refining course/module objectives, establishing detailed grading rubrics, developing new procedures for unsupervised online exams, learning live video communication software/equipment, designing a new online course in Canvas, and delivering it to 100 students—all without leaving his home. When compared with the previous five years of assessment data, the overall results in student project grades, course grades, and student evaluations of instructor effectiveness indicated a steady performance level through this significant change in material and life circumstances. The final student course scores increased in this offering when compared with the previous years. Student survey data also suggested a significant increase in the students’ assessment of instructor effectiveness. While there are many possible explanations, the collaborative relationships among the participants while the training, organizing, and delivering the course material specifically for online learning is a significant factor behind these positive outcomes for this case. © 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.

Exhaust Emissions from a Hybrid City Bus Fuelled by Conventional and Oxygenated Fuel

City buses are one of the main means of public transport in cities. As they move in a limited and densely populated area and are intensively exploited, it is particularly important that they are environmentally friendly. There are many ways to reduce emissions from city buses, including the use of hybrid propulsion. Another way is to use low-emission fuels. This article presents the results of the emission tests of an 18 m articulated city bus with a serial hybrid drive fuelled comparatively by conventional diesel fuel and oxygenated fuel containing 10% v/v of triethylene glycol dimethyl ether (TEGDME). The emission tests were carried out during the actual operation of the bus on a route in Poznań (Poland) and over the SORT cycles. The obtained test results were compared also with the results obtained for a conventional bus. The reduction in emissions of some exhaust components was found when the hybrid bus was fuelled with oxygenated fuel during its actual operation on the bus route. There was a reduction in CO emissions by ~50% and NOx emissions by ~10%. Almost identical levels of PM and HC emissions and smoke opacity were observed for both fuels. In the SORT cycles, the differences in the emissions obtained for both types of fuel were small. In general, for the hybrid bus, a lower influence of oxygenated fuel on emissions was recorded than for the conventional bus.

Oxygen Generation Using Catalytic Nano/Micromotors.

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.

System Approach to Electric Machines Development for Aviation Hybrid Propulsion Systems Under Economic Crisis

In this article, the process of electric machine development for aircraft with hybrid propulsion system is considered at all development stages: From the formation of technical task to the bench tests. Electric generator power of 400 kW and rotational speed of 12 000 r/min intended for aircraft with hybrid propulsion system passenger capacity of 9-19 seats was used as an example. The most problematic places and possible solutions are identified. The problems that can be revealed from each design part are considered and its influence on the entire development process is analyzed. We analyzed the influence of technological parameters in the prototyping on the accuracy of computer simulation. We also described the accident that occurred during the testing of the experimental sample, analyzed the causes of its occurrence and identified the consequences.

On the effect of biofouling on the minimum propulsion power of ships for safe navigation in realistic conditions.

This study first examines the minimum power requirements of a tanker according to the IMO 2013 Interim Guideline (IMO 2013). For the estimation of the added resistance in waves a recently introduced semi-empirical method is used. Secondly, the influence of the increase in surface roughness of the hull and propeller due to fouling is investigated, reflecting the actual condition of a ship in service. The results show that even if ships are fulfilling the IMO 2013 Guideline, they may become unsafe in operation. Lastly, the uncertainties involved in the assessment procedure are discussed. The investigation conducted is particularly of interest for the assessment of the safety of ships now being idle or used as floating storage due to the impact of the pandemic COVID-19 on the world economy, while they are expected to go again into service once the demand for transport recovers.