## 1 Introduction
### Literature Review
The Accimap approach is applicable to the analysis of accidents for planning, management, and organization, which can influence causality and accidents. [PERSON] et al. applied the Accimap approach to investigate the Sewol Ferry accident and analyzed not only ships, but also the related organizations, institutions, and systems [19]. However, indirect cause analysis was impossible because only the functions of the subjects related to the accident were shown. The Human factors analysis and classification system (HFACS) framework for accident investigation is an accident analysis method for human factors based on the Swiss cheese model. First developed for the investigation of aviation accidents in 1997 [20], the HFACS can systematically investigate the human factors of accidents and explain the effects of human errors, related causes, and sub causes in detail. [PERSON] et al. identified the sub-causes of engine room fires and developed an HFACS-Machinery spaces on ships framework, whereas [PERSON] developed HFACS-Passenger vessel for the validity or scope of the analysis and varied depending on the determination of the condition level [21]. Limitations in the expression of the detailed accident analysis results were also observed. [PERSON] suggested the systems theoretic accident model and process (STAMP) as a constraint-based model focused on the inappropriate control or enforcement of safety-related constraints on complex system designs, developments, and operations [22]. Moreover, setting up accident prevention measures is easy because STAMP can determine the cause through an in-depth analysis of human errors related to complex systems. [PERSON] proposed a process for designing a marine safety management system based on STAMP [23]. To show the interactions and dynamics between the functions of each system at a glance by modeling variability and nonlinear dependencies, [PERSON] proposed FRAM [24]. FRAM can be used to account for complex accidents and identify hazards in dynamic systems and can be modeled to include almost any function or subsystem of the subjects. The root cause or variability of a failure or accident can be easily traced by following the connections between functions expressed based on six functions or activity characteristics, instead of a hierarchical structure. Fourth, we reviewed research on FRAM, which is a method for systematically and visually representing the human factors of accidents. [PERSON] ([PERSON] and [PERSON], 2021) analyzed the cause of the MV Prestige stranding accident using FRAM [25]. Similar to the purpose of this study, the authors inferred potential causes by tracing the variability between functions in a normal system and explained that FRAM is essential for the analysis of marine accidents. In the study performed prior to the accident, the definition of functions was limited to the ship system and the cause analysis and variability of the port system were not considered. When a ship sails, it can be viewed as a single system. However, when a ship enters and leaves a port, it is connected to the port system. Hence, when the accident site is a port, the expansion of the volatility and functional resonance becomes more complicated. [PERSON] and [PERSON] analyzed the MV Herald of the Free Enterprise capsizing accident and the collision accident of the motor tanker (MT) Hebei spirit [26], whereas [PERSON] et al. analyzed the MV Clipper Adventurer grounding accident using FRAM [27]. [PERSON] and [PERSON] performed a case study using FRAM on the LNG ship-to-ship transfer process [28]; however, no study has analyzed the connectivity between ports and ships or applied FRAM to the MV Milano Bridge accident. Finally, the key research gaps that differentiated this study from previous studies were analyzed through literature research. The purpose of marine accident investigation is to verify the simultaneous and complex causes of accidents, which are gradually becoming important in the investigation of the causes of accidents that confirm linear causality.