Plain English Meaning

Systems that work using fluid under pressure and physical moving parts, instead of electronics or computers, to make things happen on the aircraft.

Full Definition

Aircraft system designs that use a combination of pressurized fluid (hydraulics) and mechanical linkages — such as cables, rods, levers, gears, and cams — to control engine and aircraft functions, without relying on electronic computers or digital control units.

Context Anchor

Seen in discussions of aircraft engine fuel control systems, especially when comparing older mechanical fuel controls with electronic engine controls.

Derivation

‘Hydro’ comes from the Greek hydor, meaning water — used here to refer to any pressurized fluid. ‘Mechanical’ comes from the Greek mēkhanē, meaning machine or device. Together the word describes a system that runs on fluid pressure plus physical machinery — no electronics involved.