The majority of the APU's system logic is performed by which component?

The Electronic Control Box (ECB) is the primary component responsible for overseeing the majority of the Auxiliary Power Unit (APU) system logic. This component plays a critical role in managing APU operations, including starting and stopping the unit, monitoring its performance, and managing its various functions and responses to system demands. The ECB integrates inputs from various sensors, processes this information, and executes control commands to ensure the APU operates efficiently and in a safe manner.

Other components mentioned, while important in their respective functions, do not primarily handle the APU system logic. For instance, the Bleed Management Computer (BMC) primarily manages bleed air systems but does not oversee APU control logic as thoroughly as the ECB. The Electronic Centralized Aircraft Monitoring System (ECAM) provides information and alerts to pilots regarding the status of various aircraft systems but functions as a monitoring and display system rather than a controlling unit for the APU. Lastly, the Full Authority Digital Engine Control (FADEC) is primarily focused on engine control, particularly for the main engines, rather than the operations of the APU. This refined understanding of the roles and responsibilities of each component clarifies why the ECB is the correct answer in relation to APU system management.