Which component controls the operation of the APU?

• A. APU Control Module
• B. Digital Electronic Sequence Unit
• C. Engine Control Unit
• D. Hydraulic Interface Unit

Answer: (B)

The APU is started and run under centralized sequencing logic that governs the start/stop process and safety protections. In this helicopter, that job is done by the Digital Electronic Sequencing Unit, which acts as the brain for the APU. It handles the start sequence, engages ignition, controls fuel flow to the APU, and continuously monitors critical parameters like RPM, oil pressure, and temperature. If any fault or unsafe condition is detected, it initiates a controlled shutdown and blocks the APU from running until conditions are safe again. This sequencing and interlock function is what ties the APU operation to the rest of the aircraft’s systems and ensures a safe, reliable start and run.

The engine control unit manages the main engines, not the APU; the hydraulic interface unit handles hydraulic system functions; and while there may be an APU control module for local controls, the overall operation and safety sequencing of the APU come from the Digital Electronic Sequencing Unit.