Definition
The cockpit switches that control the aircraft's magnetos, which are engine-driven devices that generate the electrical spark for the spark plugs. Most piston aircraft have two magnetos and a single ignition switch with positions for OFF, L (left magneto only), R (right magneto only), BOTH (normal operation), and START.
Plain English
The switches in the cockpit that turn the engine's spark-making devices on and off. Each engine has two of these spark-makers, and the switch lets the pilot run one, the other, or both at once.
Context Anchor
Seen in the cockpit before engine start, during the before-takeoff engine check, during shutdown, and whenever confirming the ignition is safely off before anyone moves the propeller.
Derivation
Magneto comes from 'magnet,' because these devices use spinning magnets to generate their own electricity — they don't need the aircraft battery to make spark. That's why an engine keeps running even if the electrical system fails.
Why Pilots Care
Correct use prevents accidental propeller movement, confirms each ignition system works for safety redundancy, and ensures safe engine shutdown.
Intuition Check
Do not think of magneto switches as simple battery switches. A magneto can make its own spark when the engine turns, so the ignition can still be live even with the aircraft battery off.
Example Sentence 1
During the runup, the pilot moved the magneto switch from BOTH to L, noted the small RPM drop, then back to BOTH before checking the right magneto.
Example Sentence 2
The pilot turned the magneto switch to both after the engine started to verify smooth operation on the dual ignition systems.