Causal Drivers of Sinking and Capsizing Accidents Involving Passenger Ships and Roll-on/Roll-off Ferries in Indonesia

Maritime transportation forms the backbone of archipelagic nations, where the sea functions as a primary corridor for economic activity and social connectivity. In Indonesia, passenger-ship services—including Roll-on/Roll-off (Ro-Ro) ferries are indispensable for inter-island mobility of people and goods and for sustaining regional economies [1, 2]. This connectivity enables access to essential services and markets and supports livelihoods linked to passenger transport and associated sectors. However, high dependence on passenger shipping also creates vulnerability: disruptions caused by technical unreliability or adverse sea conditions can isolate communities and generate cascading socio-economic impacts [3].

The sustainability and safety of these operations are therefore paramount. As climatic variability and operational demand intensify, passenger-shipping systems face increased exposure to environmental risk while maintaining service expectations [1, 3]. Despite their strategic role, the maritime sector—particularly in developing contexts—continues to experience a high accident burden, with passenger ships (including Ro-Ro ferries) recurrently involved in catastrophic outcomes. The persistence of sinking and capsizing/listing events highlights a critical safety deficit requiring investigation grounded in incident evidence and causal-chain logic, rather than generic attributions, to reduce loss of life and disruption.

The central problem addressed here is the continued occurrence of passenger-ship sinking and capsizing/listing in Indonesian waters—events that represent the most severe failure mode in terms of human consequences. The core challenge is to move beyond broad explanations (e.g., “poor standards”) and to identify dominant causal factors and their interactions as reproducible pathways. While international conventions define baseline requirements, Indonesia’s operational context—characterized by varied vessel conditions, high route dependence, and challenging hydro-oceanographic exposure—requires context-specific evidence to prioritize effective interventions. Accordingly, this study focuses on reconstructing how technical triggers, operational conditions, and environmental stressors combine to produce catastrophic outcomes.

Prior research provides important insights into contributing mechanisms. Studies on Ro-Ro and passenger ships have highlighted stability-relevant design features, including vulnerabilities associated with large open vehicle decks and the potential for cargo/vehicle movement under rough conditions [4, 5]. Other work emphasizes how ballast arrangements, appendages, and loading conditions can influence stability margins under rolling or asymmetric loading [6, 7]. Beyond vessel design, operational factors play a crucial role. The effectiveness of emergency evacuation procedures, for instance, is heavily dependent on crew training and passenger awareness, with design shortcomings often hindering a swift response [8]. However, these factors are often discussed in isolation, leaving uncertainty about how they combine as sequences that produce sinking/capsizing in Indonesia.

A review of closely related literature indicates that while individual risk factors—technical shortcomings, human/organizational issues, regulatory limitations, and adverse weather—are well documented, their interaction as causal chains is less consistently analyzed. Existing studies discuss monsoonal influences on transport accidents [9, 10], competency and stability considerations in Ro-Ro operations [11], and broader human-factor and work-organization risks in shipping. However, Indonesia-focused studies rarely provide a coded, cross-case typology of sinking/capsizing pathways for passenger ships (including Ro-Ro ferries) that links initiating technical triggers to environmental escalation and operational context. This is the key research gap addressed by the present study: An integrated, dataset-grounded analysis that identifies dominant causal pathways (typologies) underlying catastrophic passenger-ship losses in Indonesia.

Therefore, the objective of this study is to identify the dominant causal pathways underlying passenger-ship sinking/capsizing accidents in Indonesia, treating Ro-Ro ferries as a passenger-ship sub-category. The study tests the hypothesis that catastrophic outcomes typically reflect a cascading sequence in which an initiating technical malfunction—such as propulsion failure or blackout/power loss—reduces maneuvering control and is subsequently amplified by environmental exposure (e.g., strong currents and/or high waves), resulting in stability loss. Using National Transportation Safety Committee (NTSC) accident records from 2018–2021, the analysis produces (i) quantitative anchors (counts/proportions of coded triggers and co-factors) and (ii) a coded pathway typology supported by worked case reconstruction. The intended contribution is actionable evidence to strengthen maintenance/inspection priorities, condition-based operational limits, and crew preparedness for passenger-ship safety in Indonesia and comparable archipelagic settings.

Across the coded dataset (n = 265), the distribution of initiating trigger categories is presented in Table 7. The largest single category was T0 (not stated/insufficient information), accounting for 127 cases (47.9%), indicating an important reporting-completeness limitation in the source database. Among cases with an identifiable initiating trigger, the most frequent category was T6 (adverse weather/wave/current trigger) with 45 cases (17.0%), followed by T3 (hull breach/water ingress/structural failure) with 32 cases (12.1%), T7 (instability/cargo shift/capsize without a prior mechanical trigger) with 28 cases (10.6%), and T5 (collision/grounding/struck object) with 20 cases (7.5%). Less frequent categories included T1 (blackout/power loss) with 8 cases (3.0%), T2 (propulsion/engine/steering failure) with 3 cases (1.1%), and T4 (overloading/excess passengers or cargo) with 2 cases (0.8%). These results suggest that passenger-ship sinking and capsizing accidents in Indonesia are not driven by one overwhelmingly dominant technical trigger, but rather by a combination of environmental exposure, structural compromise, instability processes, collision-related events, and, in a smaller number of cases, loss of propulsion or maneuvering capability.

While Table 7 provides the distribution of coded trigger categories, frequency alone does not fully capture the severity or escalation potential of a given initiating condition. Some categories occur less often in the database yet remain operationally significant because they can sharply reduce response options once they occur. This is particularly important for blackout/power loss and propulsion/engine/steering failure, which together account for only 11 cases (4.2%), but may rapidly create a high-risk vessel state when they occur in narrow waterways, under strong current exposure, or during adverse sea conditions. Accordingly, the interpretation of sinking and capsizing accidents should not rely solely on how often a trigger appears, but also on how an initial disruption interacts with environmental loading and vessel condition to generate a cascading sequence toward loss of control, stability failure, and final casualty.

The KMP Yunicee case provides a clear example of this cascading mechanism. In this case, the accident sequence began with a reported blackout/power-loss condition, which immediately reduced the vessel’s propulsion and maneuvering capability. In a high-current operational corridor such as the Bali Strait, this loss of control was critical because it left the vessel unable to maintain heading, counter drift, or respond effectively to external hydrodynamic forces. Once the vessel entered this compromised state, the surrounding environmental conditions acted not merely as background context but as active escalation factors that intensified the consequences of the initial technical disruption.

The analytical significance of the KMP Yunicee case lies in the way it illustrates the transition from an initiating trigger to a catastrophic outcome through a linked sequence of interacting conditions. The blackout itself did not automatically produce sinking; rather, it created a vulnerable vessel state. That state was then amplified by strong currents, limited maneuvering space, and reduced recovery capacity under environmental loading. In this sense, the accident can be interpreted as a cascading sequence consisting of: (1) blackout/power loss, (2) loss of propulsion and maneuverability, (3) intensified exposure to current and wave action, (4) progressive loss of stability, and (5) sinking. This reconstruction is analytically important because it demonstrates how even a relatively less frequent trigger category can produce a disproportionately severe outcome under certain operating conditions.

Taken together, the cross-case coding and the KMP Yunicee reconstruction indicate that the dominant safety problem is not simply the recurrence of one specific trigger, but the repeated emergence of vulnerable vessel states that can rapidly escalate under environmental loading. This interpretation is consistent with literature describing stability risks in passenger and Ro-Ro ships [19] and with studies showing that severe sea states are strongly associated with accident escalation [5, 20]. The critical risk mechanism is therefore the interaction between triggering conditions and concurrent environmental forcing. When a vessel experiences blackout, propulsion or steering failure, hull breach, instability, or severe weather exposure, it can transition rapidly from controllable navigation to an increasingly unstable or uncontrolled condition. This helps explain why sinking and capsizing events are disproportionately fatal, even when they are not the most frequent accident types overall.

Human and organizational factors remain important upstream contributors to these accident pathways. The coded trigger categories should not be interpreted as purely immediate technical events detached from the broader management context. Many initiating conditions are shaped by antecedent decisions related to maintenance regimes, inspection quality, loading control, route planning, and weather-based operational judgment. Decisions to sail under marginal sea-state conditions may similarly reflect commercial pressure, schedule constraints, and weaknesses in organizational safety culture [21]. Accordingly, strengthening competency-based training, Crew Resource Management (CRM), loading discipline, and safety leadership should be viewed as critical control layers that can reduce both initiation risk and escalation risk [18, 22].

Overall, the observed risk profile supports a shift from localized interventions to a systems-oriented national maritime safety strategy, given the socio-economic impacts of major passenger-ship disasters on coastal communities [23]. Two evidence-linked priorities follow directly from the coded pathway results. First, technical and structural resilience should be strengthened to reduce the occurrence and consequences of initiating triggers, including blackout/power loss, propulsion or steering failure, and hull breach/water ingress, through consistently enforced maintenance, inspection, watertight integrity, and redundancy standards for both primary and auxiliary systems [5]. Second, escalation control should be improved by implementing nationwide, condition-based operational limits (weather/sea-state/current thresholds) for passenger-ship routes, supported by real-time environmental information and clear go/no-go decision rules [24]. These recommendations remain context-sensitive to the present dataset, but they provide analytically grounded direction for improving passenger-ship safety in Indonesia.