Which of the following components is NOT operated by the primary hydraulic system?

The rudder trim tab is the component that is not operated by the primary hydraulic system in the T-6 aircraft. In contrast, the other options—nosewheel steering, flaps, and landing gear—are all critical flight control systems that rely on the primary hydraulic system for their operation.

The primary hydraulic system provides the necessary hydraulic pressure to actuate the landing gear, allowing it to retract and extend during flight. It also controls the flaps, which are essential for changing the aircraft’s lift characteristics during takeoffs and landings. Additionally, the nosewheel steering, which enables precise control of the aircraft while taxiing, is another aspect of the hydraulic system's functionality.

The rudder trim tab, however, is adjusted mechanically through cables and does not rely on hydraulic pressure for its operation. This distinction is important because it highlights the difference between the components powered by hydraulic systems and those that do not require hydraulic assistance for their functionality. Understanding this aspect is crucial for maintaining and operating the aircraft effectively.