## 1 Introduction
This pilot study, conducted in 2021, employed survey-based data collection to investigate occupational health and safety concerns among aircraft maintenance machinists. Similarly, an expert-driven questionnaire was designed to assess critical human risk factors for aircraft maintenance technicians, enabling the categorization of risk factors based on survey results [15]. However, while extensive questionnaire-based data collection provides valuable insights into workload-related risks, it remains inherently vulnerable to observer subjectivity and individual variability [16]. Moreover, the potential for errors arising from subjective judgment cannot be entirely eliminated [17]. To achieve precise quantification of musculoskeletal overuse, quantitative methods such as 3D motion capture [18; 19] and biomechanical modeling [20; 21] based on anthropometric parameters [22; 23] have been introduced. Despite their high level of accuracy [24; 25], these techniques are often impractical for routine risk assessment due to their high cost [26; 27]. Additionally, 3D motion analysis technology is primarily designed for motor skill quantification [28] rather than for simultaneously analyzing the three dominant influencing factors--loading duration, human posture, and force/loading intensity [11]. To bridge the gap between subjective judgment and technological constraints, survey-based tracking instruments have been developed to minimize human assessment errors while overcoming technological limitations [29]. These advanced approaches refine REBA/RULA assessments, enhancing workplace safety by providing more precise ergonomic evaluations. For example, a semi-automatic RULA evaluation tool utilizing the Microsoft Kinect v2 depth camera was designed for real-time and offline detection of awkward postures with greater accuracy [30; 31]. Additionally, other tracking technologies, such as inertial motion capture systems, have been integrated with conventional ergonomic assessment methods to provide more granular insights into the biomechanical risks associated with aircraft maintenance tasks [32]. The integration of motion-tracking technology into postural risk assessments has facilitated more intuitive monitoring of hazardous postures in working durations [33] and enabled real-time ergonomic analyses. However, the survey-based tracking instruments introduced so far cannot be universally applied, as they address only partial aspects of WMSDs during aircraft maintenance, typically covering one or two of the three dominant influencing factors. Finally, when assessing the impact of physical loading intensity, model simulations are a widely utilized approach. [PERSON] et al. (2015) introduced a motion data-driven framework that integrates ergonomic analysis with 3D virtual visualization of the workplace, enabling a comprehensive risk assessment of musculoskeletal strain [34]. This approach first evaluates worker motions for potential ergonomic risks and then employs biomechanical simulations to estimate internal joint loads, refining both movement patterns and workplace design to enhance safety. However, this approach also addresses only a limited subset of WMSD-related factors. In summary, the advancement of ergonomic assessment methods has increasingly shifted toward quantitative approaches, yet existing techniques still exhibit notable limitations. Current methods often rely on one or two isolated indicators to evaluate workload-related risks, failing to capture the inherently dynamic and continuous nature of work. For a comprehensive workload assessment, it is essential to simultaneously consider three dominant influencing factors--loading duration, human posture, and force/loading intensity--ensuring a more holistic and accurate evaluation of occupational risks [11]. Reliability Engineering is a structured engineering discipline grounded in mathematical principles, particularly probability theory and statistics, aimed at the systematic and rigorous analysis of functional issues in components and systems to achieve a reliable design [35].