What is the function of magnetos in a piston-engine ignition system?

• A. They regulate fuel mixture.
• B. They measure engine RPM.
• C. They provide independent ignition to spark plugs, powered by engine-driven magnetos.
• D. They control propeller pitch.

Answer: (C)

Magnetos provide independent ignition for the engine’s spark plugs, powered by the engine itself. They’re engine-driven devices that generate the high voltage needed to fire the spark plugs at the precise moment the piston is at the right position for ignition. This means ignition can occur even if the aircraft’s battery or alternator fails, which is why magnetos are a critical, redundant part of piston-engine ignition.

In operation, as the engine turns, the magneto’s rotating magnets induce voltage in a coil, and the timing mechanism triggers a spark when the spark plugs should fire. This ignition system is separate from the fuel system, and it’s not what controls fuel mixture, measures engine RPM, or governs propeller pitch.