## 3 Case Study: Structural Factor Analysis for Public Transportation Bus
### Result Analysis
#### 3.5.1 Cause Group Analysis
In maintenance management decision-making, priority should be given to conducting frequent inspections and preventive maintenance for components involved in such critical factors, as well as allocating human and material resources accordingly. The alternator belt components (CF28) rank the second cause degree and the eightteenth centrality degree. The high cause degree indicates that the alternator belt components substantially influence other factors within the vehicle system. The alternator belt connects the alternator to the engine, enabling the alternator to generate electrical power while the engine runs. This power is crucial for charging the battery and powering essential electrical systems. If the alternator belt fails, it can cause rapid battery depletion, malfunctions of essential systems, and potential engine overheating. The lower centrality degree indicates that though alternator belt components frequently fail, they do not play a central role within the overall interaction network. The impact of CF28 is primarily localized and does not lead to widespread vehicle system disruptions. CF28 primarily serves as a critical trigger factor and its impact is significant but relatively isolated. For similar reasons, lubricating oil (CF6), transmission cable (CF3), EBS valve (CF15), and EBS sensor wire (CF14) are ranked high in cause degree but low in centrality degree and deserve more attention during maintenance management. Although these factors do not cause widespread system disruptions, their potential risks should not be overlooked. In maintenance decision-making, the high-cause and low-centrality factors require regular inspections and preventive maintenance to address their propensity for failure. The engine speed sensor (CF8) has a positive but relatively low cause degree compared to the factors mentioned above in the cause group. Despite this, its importance degree is the highest among all the factors. This indicates that while the engine speed sen sor (CF8) is not a primary driver of faults, it plays a critical role in the system's overall structure. The high (\(D+R\)) value reflects its extensive interactions with other components. Such factors may not directly cause failures but their occurrence can have widespread impacts on the systems. The engine speed sensor is a crucial component that monitors the rotational speed of the crankshaft. This sensor provides information to the engine control unit (ECU), which uses the data to manage fuel injection, ignition timing, and other engine functions. In addition, for similar reasons, the electrical appliance central control system (CF29), engine cylinder (CF10), and diesel injector (CF9) are ranked low in cause degree but high in centrality degree. The impact of such factors primarily lies in its potential to propagate failures through the system due to its high dependency on other components. Although these factors are not the primary causes of failures, they occupy a central position in the vehicle system and still require attention in maintenance management. Therefore, low-cause and high-centrality factors still require attention in maintenance management. The shock absorber (CF22) is a critical component of the suspension system. The shock absorber is designed to absorb and dampen the vibrations caused by uneven road surfaces. As Table 5 shows, the shock absorber (CF22) has the lowest value of (\(D-R\)) among the cause group factors, which indicates that it is a net receiver. Additionally, the value of (\(D+R\)) for the shock absorber (CF22) is also relatively low, which suggests that it has a limited overall impact. The combination of low (\(D-R\)) and low (\(D+R\)) values implies that the shock absorber (CF22) neither significantly influences other components nor holds a central position in the system's interactions. In addition, for similar reasons, air brake dryers (CF18), balance levers (CF21), and brake system air hoses (CF16) are ranked low in cause degree but high in centrality degree.