12.20 Ignition Systems – Magneto Ignition

12.20.2 Describe the principal features of a typical magneto ignition system (dual, independent, engine-driven magneto systems with two spark plugs per cylinder).

A typical aircraft magneto ignition system consists of two independent, engine-driven magnetos, each supplying spark to a separate set of spark plugs in every cylinder.

Each cylinder is fitted with two spark plugs, one connected to each magneto. This provides:

• Redundancy – the engine will continue to run if one magneto fails
• Improved combustion efficiency – two sparks promote more complete and even burning of the fuel–air mixture

Each magneto is a self-contained unit that generates its own electrical energy and does not rely on the aircraft’s electrical system. The main components include a rotating magnet, primary and secondary coils, contact breaker points, a condenser, and a distributor.

As the magnet rotates, it induces a current in the primary coil. When the contact breaker opens, the magnetic field collapses rapidly, inducing a high voltage in the secondary coil. This high voltage is then directed by the distributor to the appropriate spark plug at the correct time in the engine cycle.