Which item is not listed as being powered by the hydraulic system?

• A. Landing Gear
• B. PTCU
• C. Rudder
• D. Cabin pressure system

Answer: (D)

The main idea is understanding which aircraft systems are driven by hydraulic power versus other energy sources. Hydraulic power uses pressurized fluid to drive actuators that move large, heavy components. Landing gear relies on hydraulic actuators to extend and retract smoothly and with enough force. The rudder is typically actuated by hydraulic pistons to provide the necessary control authority, especially at high speeds and pressures. The PTCU (a control unit in the hydraulic system) helps route and regulate this hydraulic power to the appropriate actuators, so it’s part of the hydraulic actuation chain. The cabin pressurization system, however, is not driven by hydraulics; it uses bleed air and environmental control logic, with valves and electric motors managing cabin pressure and conditioning. Therefore, the cabin pressure system is not powered by the hydraulic system.