Definition
A hydraulic system is an aircraft system that uses pressurized fluid, typically a specialized hydraulic oil, to transmit force from one point to another in order to operate components such as landing gear, flaps, brakes, and flight controls. The system consists of a reservoir holding the fluid, a pump that pressurizes it, lines that carry the fluid, valves that direct its flow, and actuators that convert fluid pressure into mechanical movement.
Plain English
A network inside the aircraft that pushes oil through pipes under pressure to move heavy parts, such as the landing gear or brakes, with much less effort than would be possible by hand or muscle alone.
Context Anchor
Seen in aircraft systems discussions, preflight checks, abnormal procedures, and maintenance descriptions for items such as brakes, landing gear, and flight controls.
Derivation
From the Greek 'hydor' meaning water and 'aulos' meaning pipe. Originally referred to systems using water in pipes; today the fluid is usually a specialized oil, but the principle of moving force through a confined fluid is the same.
Why Pilots Care
It lets the pilot move large surfaces and heavy mechanisms reliably with little physical effort while keeping aircraft weight low.
Analogy
It is like squeezing one end of a sealed fluid-filled tube and having that push appear at the other end. The liquid carries the force to where the work needs to happen.
Grounding Statement
Picture pressing a brake pedal and hydraulic fluid carrying that force to the wheel brakes.
Intuition Check
Do not assume “hydraulic” means the system uses water. In aircraft, it means force is carried by pressurized liquid, usually a special hydraulic fluid.
Example Sentence 1
Before takeoff, the pilot checked the hydraulic system pressure to confirm the brakes and gear would operate normally.
Example Sentence 2
A hydraulic system failure required the crew to use manual backups for the landing gear.