Nowadays, the need for public transportation keeps on growing rapidly. One of the globally rapidly growing transportation modes is the Train. Train operation has something to do with the signaling system. Communications-based train control (CBTC) is one of the modern types of signaling systems based on two-way communication using radio waves between Wayside and Onboard devices. CBTC System is a fully automated system that requires robust maintenance of many components in order to prevent failure. Even after the maintenance, a CBTC failure may still occur. Focused on the Onboard CBTC device, a Reliability Centered Maintenance (RCM) method is adopted as an effort to discover the severity level of failure and what kind of maintenance should be given to the Onboard CBTC device. FMEA and FTA methods are also included in the RCM method to conduct the evaluation. The evaluation result indicates that Remote Input Output (RIO) is the most vulnerable equipment to experience failure, in severe conditions, it’s resulting in an emergency brake and threatening the safety of passengers. It also indicates that the frequently unclear reports from field officers and different directions from the control center significantly impact poor handling, resulting in delayed traveling. In addition to the need for maintenance, this research is also aimed at producing guidelines in form of a Standard Operating Procedure (SOP) for dealing with field failure during operating hours. It is expected that any different direction from the control center and engineer’s action can be eliminated in dealing with the Mainline  failure.