Which component controls the APU start and operation?

Which component controls the APU start and operation?

• A. APU Start Unit
• B. Electronic control box (ECB)
• C. APU Controller
• D. Control Module

Answer: (B)

The electronic control box is the one that handles the start sequencing and supervision of the APU. When you press the APU start switch, the ECB receives the command and starts the sequence: energizing the starter, opening the fuel valve, and enabling ignition as needed. It watches critical parameters such as N2, EGT, and oil pressure, and it will hold or abort the start as conditions dictate. Once the APU reaches the required speed and all limits are satisfied, the ECB transitions the unit to idle and disconnects the starter. The APU Start Unit might provide the initial energization, but it doesn’t manage the full start sequence or monitor operation. The APU Controller and Control Module are not the primary logic that conducts start and operation in this architecture; they don’t autonomously perform the end-to-end start and run supervision like the ECB does.

The electronic control box is the one that handles the start sequencing and supervision of the APU. When you press the APU start switch, the ECB receives the command and starts the sequence: energizing the starter, opening the fuel valve, and enabling ignition as needed. It watches critical parameters such as N2, EGT, and oil pressure, and it will hold or abort the start as conditions dictate. Once the APU reaches the required speed and all limits are satisfied, the ECB transitions the unit to idle and disconnects the starter.

The APU Start Unit might provide the initial energization, but it doesn’t manage the full start sequence or monitor operation. The APU Controller and Control Module are not the primary logic that conducts start and operation in this architecture; they don’t autonomously perform the end-to-end start and run supervision like the ECB does.