Definition
Hydraulic fluid that has been forced under high pressure by a pump so that it can transmit force through hydraulic lines to operate aircraft components such as the landing gear, brakes, and flaps.
Plain English
Liquid inside the airplane's hydraulic system that has been squeezed to high pressure by a pump, so it can push parts like the landing gear up or down when the pilot selects a position.
Context Anchor
Seen in landing gear system descriptions, especially when explaining how retractable landing gear extends, retracts, and locks.
Derivation
Hydraulic' comes from the Greek 'hydor' meaning water, because early systems used water to transmit force. 'Pressurized' simply means raised to a higher pressure than the surrounding air. Together they describe a fluid (today usually a special oil, not water) that has been pumped up to high pressure so it can do mechanical work.
Why Pilots Care
Adequate pressure in the fluid ensures the landing gear extends and retracts on command and that brakes function when needed.
Grounding Statement
When the gear handle is moved, the system uses pressurized hydraulic fluid to push the gear mechanism in the selected direction.
Intuition Check
Pressurized does not mean the fluid is explosive or simply stored in a container. It means force is being applied to the fluid so the fluid can push parts of the airplane system.
Example Sentence 1
When the pilot selected gear down, pressurized hydraulic fluid flowed to the actuators and lowered the wheels into position.
Example Sentence 2
A leak allowed pressurized hydraulic fluid to escape, so the gear had to be lowered by gravity.