## 1 Introduction  
Air transportation has emerged as a crucial and efficient means of transporting people, cargo, and mail via airplanes and other aircraft, positioning itself as a foundation of modern transportation. Ensuring the safe operation of air transportation heavily relies on the motor behaviors of aircraft maintenance personnel, which are influenced by numerous factors. A recent study highlighted that the demanding nature of aircraft maintenance, characterized by high physical loads, extended work durations, and challenging environmental conditions, significantly increases the risk of work-related musculoskeletal disorders (WMSDs), leading to a notable decline in motor performance [1]. WMSDs are attributed to the overuse of the human musculoskeletal system [2]. Due to the often subtle onset of WMSD symptoms among maintenance personnel, timely detection and control remain particularly challenging [3]. Consequently, biomechanical risk assessment during aircraft maintenance is essential for reducing the prevalence of occupational illnesses and enhancing work efficiency [4]. With the rapid growth of the air transportation industry over the past half-century, research in this domain has gained prominence as a critical area within ergonomics studies globally. At the close of the 20 th century, ergonomic audit software systems were introduced to enhance the performance of aircraft inspectors [5]. In the 21 st century, greater attention has been given to the workloads experienced by aircraft maintenance personnel. [PERSON] et al. (2022) highlighted that these workers are often subjected to physically and psychologically demanding environments [6]. The complexity of maintenance tasks can lead to varying degrees of muscle fatigue, thereby affecting overall work effectiveness. [PERSON] et al. (2013) examined the physical fatigue experienced during aviation maintenance by analyzing human error data, developing a human error impact and prevention model, and exploring the causes of errors within the human-machine environment [7]. [PERSON] et al. (2022) refined accessibility evaluations by integrating comfort as a factor in virtual maintenance models, thus improving the precision and accuracy of maintenance fatigue assessments [8]. These factors significantly influence the quality of aviation maintenance, necessitating research to enhance safety and efficiency within maintenance environments [9]. However, the collective and dynamic nature of motor behavior poses challenges in quantifying the risk factors impacting work effectiveness [10]. This highlights the urgent need for new methodologies to address these challenges and close existing gaps in risk quantification. The present study aims to address this need by developing a novel biomechanical framework to quantify dynamic risks in motor behaviors during aircraft maintenance. Survey-based ergonomic assessment tools have long been a cornerstone of workplace risk evaluation, providing practical and accessible means of identifying ergonomic hazards caused by three dominant influencing factors--loading duration, human posture, and force/loading intensity [11]. Among these, two of the most widely utilized methods are the Rapid Upper Limb Assessment (RULA) [12] and the Rapid Entire Body Assessment (REBA) [13]. While RULA is designed to evaluate the upper extremities during work tasks, REBA extends its scope to encompass full-body postures. Both methods assess key biomechanical factors, including body posture, movement type and repetition, joint and/or segmental range of motion, and coupling, making them particularly well-suited for analyzing the risk working postures prevalent in service industries. Building on these foundational models, specialized survey-based assessment tools have been developed to address the unique risks encountered in aircraft maintenance. For instance, the effects of task duration on aircraft maintenance personnel are predominantly evaluated through questionnaire surveys [14].