Definition
Aircraft systems that transmit force and motion by means of a confined fluid under pressure. Hydraulic systems use a liquid (typically a special hydraulic oil), and pneumatic systems use a compressed gas (typically air or nitrogen). The pressurized fluid is routed through lines to actuators that move components such as landing gear, flaps, brakes, and flight controls.
Plain English
Systems that use a pressurized liquid or gas to do work on the aircraft, like raising the gear, applying the brakes, or moving the flaps.
Context Anchor
Seen in aircraft systems study, maintenance manuals, and checklist procedures involving brakes, landing gear, flaps, or system pressure.
Derivation
From Latin fluidus, meaning 'flowing.' A fluid is anything that flows, which includes both liquids and gases. 'Fluid power' simply means power transmitted by a flowing, pressurized substance — making it the umbrella term that covers both hydraulic and pneumatic systems.
Why Pilots Care
These systems enable reliable operation of critical controls and landing gear; leaks or failures can affect safety and require prompt maintenance attention.
Grounding Statement
A fluid power system works by putting pressure into liquid or air and using that pressure to move something elsewhere in the aircraft.
Intuition Check
“Fluid” does not mean only liquid here. In fluid power, the fluid may be hydraulic liquid or compressed air or gas.
Example Sentence 1
The aircraft's fluid power systems include a hydraulic system for the landing gear and brakes, and a pneumatic system for the door seals.
Example Sentence 2
Loss of fluid pressure in the power systems caused the landing gear to extend slowly.