Which hydraulic component assists with nosewheel steering?

The nosewheel steering actuator is crucial for controlling the direction in which the aircraft's nosewheel turns, allowing for effective steering during taxiing, takeoff, and landing operations. When the pilot manipulates the tiller or rudder pedals, the actuator translates these inputs into mechanical movement of the nosewheel, enabling precise maneuverability of the aircraft on the ground.

The other components listed serve different functions. For instance, the upper rudder PCU primarily manages the lateral control of the aircraft via the rudders and is not involved in the steering of the nosewheel. The inboard emergency brakes are designed for braking purposes and do not impact steering. Lastly, the main landing gear supports the aircraft during landing and takeoff rather than providing steering capabilities. Thus, the nosewheel steering actuator is essential for directing the aircraft on the ground, making it the correct answer.