Which of the following systems is NOT powered by the AC system?

• A. SAS actuators
• B. Fire detection system
• C. Fuel shutoff valve
• D. All are powered

Answer: (D)

The correct answer is that all systems mentioned are not powered by the AC system. The SAS (Stability Augmentation System) actuators typically rely on electrical power from DC sources rather than AC power, enabling them to function effectively without dependence on alternating current.

The fire detection system also commonly operates on a DC supply which is more reliable for continuous monitoring and immediate response. Furthermore, the fuel shutoff valve is usually actuated by a DC motor or solenoid rather than powered by an AC source, ensuring rapid action to either allow or halt fuel flow in response to various conditions.

Understanding the specific power requirements for each of these components clarifies why they are not reliant on the AC system, underlying the importance of the appropriate power sources for different aviation systems.