Definition
The force per unit area exerted by a confined liquid (typically a specialized hydraulic fluid) within an aircraft's hydraulic system, used to transmit power to operate flight controls, landing gear, brakes, and other actuated components.
Plain English
The push created by trapped fluid in the aircraft's plumbing. Because liquid doesn't compress, that push can be sent through pipes to move heavy parts of the aircraft with very little effort from the pilot.
Context Anchor
Seen in discussions of hydromechanical flight controls, landing gear, brakes, and other aircraft systems that use pressurized fluid to do work.
Derivation
Hydraulic' comes from the Greek hydor (water) and aulos (pipe), literally 'water through a pipe.' Early hydraulic systems used water; modern aircraft use specialized fluids, but the principle is the same — pressurized liquid moving through lines to do work.
Why Pilots Care
It allows reliable movement of large control surfaces and critical systems with minimal pilot effort, directly affecting handling and safety during normal and emergency operations.
Analogy
Think of squeezing a sealed syringe full of liquid. The liquid cannot easily compress, so your push is carried through the liquid to move the other end. Aircraft hydraulic systems use the same basic idea, but with stronger parts and controlled pressure.
Intuition Check
Hydraulic pressure does not mean the amount of hydraulic fluid in the system. It means how hard that fluid is pushing inside the system.
Example Sentence 1
When hydraulic pressure dropped to zero, the crew followed the checklist to extend the landing gear using the backup system.
Example Sentence 2
A drop in hydraulic pressure caused the landing gear to extend more slowly than normal.