Definition
A connected set of gears that transmits motion from one rotating shaft to another, typically changing speed, direction, or torque in the process. In a reciprocating aircraft engine, the gear train is the system of meshed gears driven by the crankshaft that turns accessories such as the magnetos, oil pump, fuel pump, and camshaft.
Plain English
A series of gears that mesh together so that when one turns, it drives all the others. In an engine, it's how the spinning crankshaft also drives the parts that need to turn with it.
Context Anchor
Seen in engine and induction-system discussions, especially where an engine-driven part such as a supercharger is connected to the engine by gears.
Derivation
‘Train’ here means a connected sequence — like a train of thought or a train of cars — where each part follows and depends on the one before it. A gear train is simply a sequence of gears linked together so motion passes through them in order.
Why Pilots Care
The gear train keeps the supercharger spinning at the right speed so the engine can produce full power at higher altitudes.
Intuition Check
This does not mean the aircraft’s landing gear, and “train” does not mean a railroad train here. A gear train is a connected set of turning toothed wheels inside a machine.
Example Sentence 1
The crankshaft drives a gear train that turns the camshaft and the magnetos at the correct speed.
Example Sentence 2
Mechanics check the gear train for wear during overhaul because damaged teeth can stop the vacuum pump and other accessories.