Which statement describes a servo in flight control systems?

• A. A sensor that detects changes in fluid pressure.
• B. A type of flight control surface used only on tail surfaces.
• C. A motor or other form of actuator which receives a small signal from the control device and exerts a large force to accomplish the desired work.
• D. An electrical switch controlling engine ignition.

Answer: (C)

In flight control systems, a servo is an actuator that takes a small control signal and uses it to produce a much larger movement or force to position a control surface. The idea is signal amplification: the pilot’s control device or an automatic flight controller sends a tiny command, and the servo converts that into the actual movement that deflects the surface against aerodynamic loads. This can be done with electric motors or hydraulic actuators, providing the necessary force to move ailerons, elevators, or rudders accurately and reliably.

Why this fits best: the essence of a servo is the capability to take a small input and generate a large, controlled output to do the work of moving surfaces. Other descriptions describe sensors that detect changes, surface types that aren’t limited to tail surfaces, or ignition switches, none of which capture the actuation and amplification role of a servo in moving flight controls.