Which component is used for starting the APU?

• A. A hydraulic actuator
• B. An electric motor
• C. A hydraulic starter
• D. A capacitor

Answer: (C)

The correct answer is associated with the use of a hydraulic starter for initiating the Auxiliary Power Unit (APU). Hydraulic starters are specifically designed to provide the necessary torque to start an APU, utilizing hydraulic pressure generated from the aircraft's hydraulic system.

The use of a hydraulic starter is advantageous because it can deliver high starting torque while being lightweight and compact. These starters enable a smooth and efficient startup process, particularly vital for APUs that may need to operate in various conditions and environments.

In contrast, while an electric motor can be used to start some engine types, it is not the conventional method for APUs in many aircraft. A hydraulic actuator and a capacitor serve different purposes altogether, with actuators typically involved in mechanical movement and capacitors used for electrical energy storage, not for engine starting.