Definition
Small hydraulic or pneumatic actuators that mechanically release the uplocks holding the landing gear in the retracted position, allowing the gear to fall free and extend by gravity when normal hydraulic pressure is unavailable.
Plain English
Little powered pistons that pop open the latches holding the landing gear up inside the airplane, so the gear can drop down on its own when the normal system has failed.
Context Anchor
Seen in emergency landing gear extension procedures and system descriptions for retractable-gear airplanes.
Derivation
Uplock simply means the lock that holds the gear up. Release cylinders are small cylinder-shaped actuators that release something. Together: the cylinders that release the up-locks.
Why Pilots Care
These cylinders let the pilot extend the landing gear when hydraulic power is lost, reducing the chance of a gear-up landing.
Intuition Check
Do not assume these cylinders push the landing gear all the way down. Their main job is to release the locks that are holding the gear up.
Example Sentence 1
When the pilot activated the emergency extension handle, the uplock release cylinders unlocked the gear and it free-fell into the down position.
Example Sentence 2
During the preflight inspection the mechanic checked the uplock release cylinders for leaks to confirm they would work if needed.