Definition
A small gear, usually with a relatively low number of teeth, that meshes with a larger gear or a toothed rack to transmit motion or change mechanical advantage.
Plain English
A small gear that drives a bigger gear, or runs along a straight toothed bar to make something move.
Context Anchor
Seen in aircraft maintenance descriptions of gear-driven mechanisms, such as landing gear, flap, trim, or control-system parts.
Derivation
From the French 'pignon', meaning the gable of a roof or the cog of a wheel, ultimately from Latin 'pinna' (point, peak). The teeth of a small gear resembled the points along a gable, giving the part its name.
Why Pilots Care
Many aircraft systems — starters, trim wheels, flap drives, and some landing gear mechanisms — rely on a pinion meshing with a larger gear or rack. Knowing the term helps when reading maintenance manuals or troubleshooting why something isn't moving smoothly.
Intuition Check
A pinion is not just any small gear in casual use — in aviation maintenance it specifically means the smaller of two meshing gears, or the gear that drives a rack.
Example Sentence 1
The starter motor's pinion engages the engine's ring gear to crank the engine during start.
Example Sentence 2
Technicians check the pinion teeth for wear before reinstalling the propeller gearbox.