Improvement and analysis of aircraft maintenance flow process using lean manufacturing, PDCA, PICA, and VSM for sustainable operation system

The aircraft maintenance process plays a crucial role in ensuring the safety and reliability of air travel. However, this process often encounters inefficiencies and waste, reducing productivity. This study aims to analyze the flow of the aircraft maintenance process and identify areas for improvement using Lean Manufacturing, Plan-Do-Check-Act (PDCA), Problem Identification and Corrective Action (PICA), and Value Stream Mapping (VSM) methods within a sustainability system. This study demonstrates how non-value-adding (NVA) and necessary but non-value-adding activities (NNVA) contribute to maintenance process delays, waste generation, and decreased process efficiency. It also underscores the impact of waste on process performance and proposes potential time savings through focused improvements. The result revealed that inventory wastage was the most prevalent issue, accounting for 9 out of 26 activities, followed by waiting for wastage with seven activities and defects with 5 activities. These wasteful activities are primarily concentrated in phases 3, 4, and 5, encompassing inspection, repair, and installation phases. Consequently, there is a pressing need to enhance efficiency in all phases, particularly phases 3, 4, and 5, by targeting non-value-added activities. Implementing these improvements can reduce the total process time from 18,229 minutes to 15,170.2 minutes, offering a detailed roadmap for enhancing the aircraft maintenance process. Thus, this study is an alternative consideration for the aircraft maintenance industry to ensure a continuous improvement process in facing the challenges of global industry innovation as the category of Sustainable Development Goals (SDGs).


Introduction
Industrial, Innovation and Infrastructure aspects are a Sustainable Development Goals (SDGs) category focusing on developing sustainable industrial sectors, promoting innovation and improving infrastructure.Increasing efficiency and reducing waste in the production system is one innovation and strategy to achieve this.Efficiency and waste reduction are crucial in aircraft maintenance since the Maintenance Repair and Overhaul (MRO) market is expanding due to the increasing air traffic.To manage operational and maintenance expenses, several aircraft owners worldwide are purchasing new aircraft [1].The cost of operating a business was significantly impacted by waste.As a result, there was an increased need to cut maintenance expenses to maintain profitability.Therefore, MROs must identify their internal reserves, streamline their internal workflows, and be laser-focused on pleasing their customers to come back and write another check [2].This study highlights the importance of analysis and efficiency in aircraft maintenance operations, focusing on waste reduction.Referred to as the "7 Muda" or "7 Wastes", waste in a production or service process includes transportation, inventory, movement, waiting, overprocessing, overproduction, and defects.It has been proven to have a detrimental impact on efficiency and productivity in the aircraft maintenance process.
Researchers utilize several methodologies to identify the root causes of wastage and propose improvements.Lean Manufacturing is a multifaceted strategy that integrates several managements that can combine to produce a streamlined, high-quality system that produces a smoother flow process at a rate consistent with customer demand with little to no waste [3].Plan-Do-Check-Act (PDCA) is used to plan improvements and systematically create a continuous improvement process.PDCA facilitates root cause identification and improves productivity, efficiency, and quality [4].
Furthermore, Problem Identification and Corrective Action (PICA) is used to observe the improvement process, analyze obstacles, and minimize them.PICA is one of the ingrained thought processes that became ritual in the review.It forces people to carefully study each issue before coming up with a solution [5].Value Stream Mapping (VSM) is another valuable tool used in this study.This tool maps the current state of the aircraft maintenance process and designs the future state, depicting all the critical steps involved.VSM was adapted to investigate the current state, provide input for the future state, and solve the identified problems.VSM enables the identification of waste and problems in the aircraft maintenance process.Its successful application in various service sectors has resulted in increased customer satisfaction, shorter cycle times, cost savings, improved service quality, and adequate process flow [6].
This study was conducted at Indonesia's most significant aircraft maintenance company and emphasized the importance of analysis and efficiency in the maintenance process, specifically focusing on waste reduction.It highlighted the urgent need to optimize operations and deliver outstanding maintenance services by addressing waste.Through the application of methodologies such as Lean Maintenance, Lean Six Sigma, PDCA, PICA, and VSM, this study identifies root causes, develops targeted strategies, and improves maintenance processes.By examining 10 sample aircraft maintenance projects conducted from 2020 to 2023, researchers highlighted the detrimental impact of wastage and emphasized the importance of addressing it to improve efficiency and deliver exceptional maintenance services.Provides valuable insights to eliminate waste, improve reliability, reduce costs, increase customer satisfaction, streamline processes, and improve overall service quality [7].
The urgency and relevance of this study lie in its potential to revolutionize aircraft maintenance operations, leading to improved efficiency, reduced wastage, and better service outcomes in a sustainable main.By addressing the challenges posed by wastage and implementing targeted strategies, this study contributes to knowledge in the field of aircraft maintenance, setting the stage for transformative advancements in the industry [8].
Lean manufacturing gives producers a competitive edge by reducing costs and increasing output and quality.This concept focuses on improving equipment efficiency and inventory, faults, scrap, production lead time, processing time, cycle time, set-up time, and inventory [9].To identify the root cause and find improvements that can eliminate waste, implement lean Maintenance that provides a level of reliability of a product according to needs, and at the same time, reduce maintenance costs.Implementing Lean Six Sigma to aircraft maintenance processes involves identifying areas of waste and variability and implementing improvements to increase efficiency and reduce errors in a maintenance process [10].Many companies are turning to Lean because it helps meet customer demand, increase labor productivity, reduce inventory, and increase equipment utilization.Lean and Six Sigma can be applied side by side as is.They are not mutually exclusive.Lean implementations combined with Six Sigma methods help prevent more than detect defects [11].An aircraft manufacturing company always strives to eliminate waste and non-complementary activities during the aircraft delivery process, reduce production costs and improve efficiency.
The 5S principle (Seiri, Seiton, Seiso, Seiketsu, Shitsuke) has broad potential to improve various aspects [12].In the design phase, applying 5S techniques improves information management and customizes the designer's workstation.It enables efficient information management, processing, analysis, and production by various disciplines in the design of construction projects.The proper organization of data facilitates design teams' access to relevant information promptly, reducing wait times, design process inefficiencies, and rework caused by existing information.
The Plan-Do-Check-Act (PDCA) plans improvements to aircraft maintenance processes by creating a continuous improvement process [13].The PDCA method is helpful in creating continuous improvement, which is more future-oriented, flexible, logical, and reasonable to do.PDCA is a tool that helps in identifying root causes and improving productivity, efficiency, and quality.The PDCA cycle was originally used as a tool to control product quality.However, quickly, this method was highlighted as one that allows the development of process improvement at the organizational level.The PDCA cycle is characterized by a continuous improvement approach and is recognized as a logic program that allows increased activity [14].
Problem Identification and Corrective Action (PICA) is an approach to observe the improvement process, analyze obstacles that still occur in its application, and make efforts to minimize them.PICA is one of the tools often used in Six Sigma methods at the Improvement stage.It includes alternative fixes for each cause of the problem and describes implementing those corrective actions.The data processed in the PICA method have the highest Risk Priority Number (RPN) value, which shows the highest weight affecting defects' onset.The output is an alternative fix for the previously identified cause of the problem.According to the established procedure, PICA should be taken whenever production process issues are discovered [15].
Then, Value Stream Mapping (VSM) is used to map the current state, design the future state, and describe all the essential steps in a process.VSM is adapted to investigate current conditions, input for future conditions, and solve problems identified in the maintenance process [16].The VSM approach is implemented to investigate waste in the Aircraft Maintenance Process.VSM is effective in identifying problems that occur and waste contained in the Aircraft Maintenance process.VSM has provided benefits to various industrial sectors that provide services.Value stream mapping is a tool enhanced by lean manufacturing and works best in manufacturing, shipping, or industry-oriented processes [17].

Research Method
This study used a combination of primary and secondary data to improve efficiency in the aircraft maintenance process.The research began with a literature study conducted parallel with field observations-problem identification and formulation followed by determining research objectives.Data collection involved two components: observation of a sample of 10 aircraft maintenance projects and distribution of questionnaires to 100 personnel.The participants were personnel from various aircraft Maintenance, Repair, and Overhaul (MRO) company departments, including production, structures, cabin, planning, quality assurance, and engineering.This comprehensive representation ensured that the data collected provided a holistic perspective of the entire aircraft maintenance process.By involving personnel from different areas of expertise, the study aimed to gather invaluable insights and firsthand experience, fostering a comprehensive understanding of the challenges faced in all aspects of aircraft maintenance.Observation data was tested for adequacy and uniformity, with further data collection undertaken where necessary.
The questionnaire focused on identifying seven wastes and evaluating the implementation of the 5S methodology.The next step was to create a current value stream mapping, incorporating the data collected from the observations and questionnaires.When the data was sufficient, the researchers developed the future value stream mapping.Finally, the study concluded by synthesizing the findings, providing recommendations, and highlighting the expected efficiency, quality, and reliability improvements in the aircraft maintenance process.The processed data became the basis for conducting PDCA and PICA analysis.The last step is creating the Future State Value Stream Map to become the basis for continuous improvement efforts.Once implemented, organizations can compare the performance against the desired future state and identify gaps or areas for further improvement.It enables a systematic and ongoing review of the process to sustain and enhance the achieved benefits.These valuable contributions enable the development of targeted strategies to address wastage issues and improve overall performance.

Result and Discussion
Data collection was carried out by direct observation of the field and interviews with parties involved in the aircraft maintenance process.Researchers have collected 10 samples of Airbus A330 Family aircraft maintenance projects from Oman Air (registration A4O-xx), Cebu Pacific (registration RPxxxxx), Nepal Airlines (registration 9N-xxx), and Wamos Air (registration EC-xxx).These projects are executed in the Wide Body Base Maintenance Division throughout 2020-2022 and consist of 7 phases, including aircraft preliminary inspection, removal phase, inspection phase, rectification phase, installation phase, final phase, and return to services as listed in Table 1.The uniformity test in this study was measured with a confidence level of 95% and an accuracy level of 5%, and the results are described in Table 2. Table 2 shows that the data uniformity test results show that the aircraft maintenance time of 10 project samples is still at the Upper Control Limit (UCL) and Lower Control Limit (LCL).Therefore, it can be concluded that all aircraft maintenance process data is declared under control.The results of the uniformity test of aircraft maintenance data can be described in the Process Control Map graph in Fig. 1.On the Process Control Map shown in Fig. 1, the maintenance time graph shows that no one exceeds either the UCL or LCL, but the Oman Air aircraft maintenance project with registration A4O-DA identified that the maintenance time almost touches the LCL limit, on the other hand the Cebu Pacific aircraft maintenance project with registration RP-C3344 almost touches the UCL limit.Process Activity Mapping is used to identify each activity in the maintenance process that is Value Added, Non-Value Added, or Necessary but Non-Value-Added to provide an evaluation so that the process can run effectively and efficiently.The following is a presentation of the results of waste identification from Process Activity Mapping to help understand waste that often occurs in the aircraft maintenance process.

Figure 1. Aircraft Maintenance Process Uniformity Test Chart
A questionnaire was conducted on 100 respondents who were directly involved in the aircraft maintenance process to determine the criteria for these activities.The answers from the results of the questionnaire that the researcher has processed have been summarized in Table 3. Table 3 shows that waste inventory is found in phase 2 to phase 6, with the potential most often occurring in phase 3, phase 4, and phase 6.This is followed by waste waiting, which occurs in Phase 1, Phase 3, Phase 4, Phase 6, and Phase 7 in second place.Moreover, in third place, there are waste defects that occur in Phase 2, Phase 4, and Phase 5.The phases with the most waste activity are Phase 3, Phase 4, and Phase 5, namely the Inspection, Repair, and Installation phases.The next step, Kaizen Blitz can be placed in all three phases.The location of the Kaizen Blitz can be seen in Fig. 2. Through the Kaizen Blitz on Current State Value Stream Mapping method illustrated in Fig. 2, it can gain a deep understanding of the ongoing aircraft maintenance process flow.It was clearly illustrated that an evenly distributed efficiency effort is required in phases 1 to 7 to achieve significant savings in changeover time.
However, phases 3, 4, and 5 are the main focal points that contain the most waste activities.There are great opportunities for improvement and efficiency in these phases, especially for activities that do not add value.Through focused improvement and savings efforts on these activities, a significant increase in efficiency can be achieved in the maintenance process.In addition to reducing the waste of valuable time and resources, these measures will also positively impact the quality of service and reliability of the aircraft maintenance process.In the long run, significant maintenance cost reductions, increased aircraft availability, and higher customer satisfaction will be the tangible achievements resulting from these efforts.
Based on Table 4, the seven types of waste are closely interrelated with the four influencing factors.Inventory and waste movement have relationships with three factors, while waste waiting, overprocessing, and defects are related to two factors.In addition, waste transportation and overproduction are related to one factor, highlighting the diverse nature of waste in the maintenance process.
Moving on to the Do stage, an important approach to reducing waste lies in implementing the wellknown 5S/5R methodology in the work area.This methodology, which includes Seiri (Sort), Seiton (Straighten), Seiso (Shine), Seiketsu (Standardize), and Shitsuke (Sustain), provides a structured framework for minimizing waste.Analysis of the survey data has revealed the linkages between each type of waste and the corresponding 5S/5R components.The in-depth linkage data is presented in Table 5, which provides a clear direction for improvement efforts.
Moving on to the Check stage, the five reasons analysis method provides a deeper understanding of the problem identification by exploring the root causes attributed to human, method, material, and system factors.This analysis allows researchers and organizations to trace the root cause of the problem at hand.These causes act as the hidden threads that weave together the complex tapestry of waste within the aircraft maintenance flow process.By delving into the depths of each causative factor, organizations can unravel the intricate web of interconnected issues, laying the groundwork for impactful improvement strategies.In the Action Stage, to realize all the plans that have been made before, researchers moved by sorting the problem factors and delving into their sources, organizations and researchers gain valuable insights to guide improvement steps effectively.The Problem Identification and Corrective Action (PICA) methodology can be seamlessly applied, empowering the identification of problems, offering improvement suggestions, and outlining implementation steps.Table 6 provides a detailed overview of the PICA process, serving as a practical roadmap for executing the meticulously crafted plans.Table 6 presents a comprehensive assessment of personnel, methods, materials, and systems related to the aircraft maintenance process.
In the personnel assessment, critical issues such as lack of understanding, inadequate preparation, and communication gaps were identified.To address these challenges, training programs, counseling sessions, safety reminders, and reward initiatives were used to improve knowledge, minimize wasteful practices, and encourage effective teamwork.Method assessments revealed errors in planning and inefficient processes, resulting in excessive workload.To optimize work within maintenance deadlines and avoid unnecessary resource allocation, careful data collection and discussions with engineers were conducted to streamline processes.Finally, the system assessment addressed challenges related to ineffective material management, imbalance in manpower allocation, limited vehicle utilization, and reliance on imported materials.The results of the implementation of PDCA and PICA then led to the Future State Value Stream Mapping as shown in Figure 3.By comparing the results obtained from Fig. 2 and Fig. 3, important insights can be gained regarding the aircraft maintenance process.The analysis revealed that an even effort across phases 1 to 7 is required to achieve significant savings in changeover time.However, phases 3, 4, and 5 contain the highest concentration of wasteful activities, thus presenting key opportunities for improvement and efficiency gains, especially in non-value-added tasks.Upon examining the Future Value Stream Mapping, time efficiencies can be achieved across all 7 phases of the aircraft maintenance process to minimize waste.
The result highlights potential time savings of up to 3,058.8 minutes by streamlining the cycle time of wasteful activities within each phase and reducing the transition time between phases.Specific activities that can be targeted for elimination or reduction include the initial aircraft inspection (saving 59.2 minutes), lifting phase (saving 114.8 minutes), inspection phase (saving 187.7 minutes), repair phase (saving 799.5 minutes), installation phase (saving 154.4 minutes), final phase (saving 54.9 minutes), and return to service phase (saving 35.5 minutes).The implementation of these improvements can effectively reduce the total maintenance time from 18,229 minutes to 15,170.2minutes, resulting in significant time savings and improved process efficiency.

Conclusion
In this study, the aircraft maintenance process faced problems such as time wastage, lack of coordination between departments, and quality problems.By applying saving methods, the treatment process reduces waste, improves coordination, and addresses quality issues.The application of Lean Manufacturing, PDCA, PICA, and VSM methods has proven to be beneficial in increasing efficiency.It is recommended that the company continue the application of these methods for further improvement.This study can also be a reference for the aviation industry to improve aircraft maintenance efficiency.The application of Lean Manufacturing involves identifying value streams, mapping processes, and the use of Lean tools such as 5S and visual management.Data from questionnaires and samples of aircraft maintenance projects showed the same percentage of waste.The PMA found 24 VA activities, 7 NVA activities, and 19 NNVA activities.The implementation of PDCA in aircraft maintenance flow process management involves plan development, plan implementation, progress monitoring, and corrective actions.This process is repeated iteratively to achieve continuous improvement.
The application of PICA in aircraft maintenance process management involves identifying and documenting problems and taking corrective actions to resolve them.Value Stream Mapping (VSM) is used in aircraft maintenance flow management for value stream identification, mapping current and future conditions, and identifying improvement opportunities.VSM helps visualize process flow, identify waste, and develop improvement plans.VSM results show waste in phases 3, 4, and 5, which are the focus of kaizen blitz.After efficiency was made to eliminate waste, the total Cycle Time and Changeover Time were successfully reduced from 18,229 minutes to 15,170.2minutes.
The scientific contribution of this study lies in its empirical demonstration of the effectiveness of Lean tools and techniques, including visual management, work standards, Lean Manufacturing, PDCA, PICA, and VSM methods, in enhancing the efficiency of aircraft maintenance processes.By implementing these methods, substantial improvements were observed in process flow, waste reduction, coordination, and overall process efficiency.The recommendation to implement a performance measurement system further contributes to future advancements by offering a means to monitor progress and identify areas for further enhancement.In conclusion, this study provides concrete evidence and valuable insights that can serve as a scientific foundation for future improvements in the aviation industry.It enables organizations to optimize their aircraft maintenance processes, thereby attaining heightened levels of operational efficiency.

References
[1] Deng Q, Santos B F, and Verhagen W J 2021 A novel decision support system for optimizing aircraft maintenance check schedule and task allocation Decision Support Systems 146, p.113545

Figure 2 .
Figure 2. Kaizen Blitz on Current State Value Stream Mapping

Figure 3 .
Figure 3. Future State Value Stream Mapping [2] Ayeni P, Ball P, and Baines T 2016 Towards the strategic adoption of Lean in aviation Maintenance Repair and Overhaul (MRO) industry: An empirical study into the industry's Lean status Journal of Manufacturing Technology Management 27(1) pp.38-61 [3] Mawlood S J, Albayatey A S W and Jassem A A 2022 Investigating the use of lean manufacturing techniques in liquid batteries production: A field research in Babylon plants Materials Today: Proceedings 60 pp.1851-1856 [4] Reményi C and Staudacher S 2014 Systematic simulation based approach for the identification and implementation of a scheduling rule in the aircraft engine maintenance International Journal of Production Economics 147 pp.94-10

Table 1 .
Calculation of cycle time, normal time, and standard time

Table 2 .
Uniformity Test Result

Table 3 .
Recapitulation of Waste Types in the Aircraft Maintenance Process

Table 4 .
The Linkage of Waste with Its Causative Factors

Table 5 .
Heat Map Waste and 5S

Table 6 .
PICA Evaluation of Factors Causing Waste