Definition
Relating to a system that transmits force and motion by pressurizing a confined liquid (typically a specialized oil) and routing it through lines, valves, and actuators to operate mechanical components.
Plain English
Powered by pressurized fluid. A pump pushes liquid through tubes to move parts that would otherwise be too heavy or stiff to move by hand.
Context Anchor
Seen in landing gear system descriptions, especially when gear is extended or retracted by fluid pressure rather than by a purely mechanical or electric drive.
Derivation
From Greek 'hydor' meaning water, plus 'aulos' meaning pipe. Originally referred to anything operated by water flowing through a pipe. In modern aircraft, the principle is the same — fluid in a pipe doing work — but the fluid is a specialized oil rather than water.
Why Pilots Care
Hydraulic systems allow reliable operation of landing gear without relying solely on mechanical or electrical means, but loss of hydraulic pressure can lead to gear-up landings if not managed properly.
Analogy
Think of squeezing one end of a sealed tube filled with liquid and having that push something at the other end. The liquid carries the push where it is needed.
Intuition Check
Hydraulic does not mean electric, even if an electric pump is involved. Hydraulic means the actual moving force is carried by pressurized liquid.
Example Sentence 1
When the pilot moved the gear lever down, the hydraulic system pressurized the lines and the landing gear extended.
Example Sentence 2
A hydraulic leak in the landing gear caused the wheels to remain retracted.