Definition
Hydraulic or pneumatic devices that convert fluid pressure into linear (straight-line) mechanical movement, used to extend or retract aircraft components such as landing gear, flaps, brakes, and control surfaces.
Plain English
Tube-shaped parts that use pressurized fluid or air to push or pull aircraft parts in and out, like the legs of the landing gear or the flaps on the wings.
Context Anchor
Seen during preflight inspection, especially when checking retractable landing gear areas for leaks, damage, loose hardware, or security.
Derivation
From Latin 'actus' meaning 'a doing' or 'movement.' To 'actuate' something is to put it into action. An actuating cylinder is literally a cylinder that puts something into motion.
Why Pilots Care
These cylinders must be leak-free and properly pressurized; failure can prevent gear extension or retraction and compromise safety.
Analogy
Think of a bicycle pump in reverse: instead of you pushing the handle to move air, pressurized fluid pushes a rod out of the cylinder to move a part of the airplane.
Intuition Check
Do not confuse actuating cylinders with engine cylinders. Engine cylinders are where combustion happens; actuating cylinders are system parts that move other airplane parts.
Example Sentence 1
During preflight, the pilot checked the landing gear actuating cylinders for hydraulic leaks and signs of corrosion.
Example Sentence 2
The landing gear would not retract because one actuating cylinder had lost pressure.