All aero piston engines are fitted with dual ignition, that is to say, two electrically independent ignition systems. Each engine cylinder has two sparking plugs fed by two separate magnetos. This reduces the risk of engine failure caused by faulty ignition and increases the power output of the engine by igniting the cylinder charge at two points (reducing combustion time).

Magnetos are self-contained engine-driven electrical generators. They produce a series of Extra High Tension (EHT) electrical sparks at the sparking plugs, in the correct firing sequence, for ignition of the petrol and air mixture.

Ignition Switch provides complete control of the engine’s magneto circuit, the magneto being made inoperative by earthing the primary circuit. In the ‘OFF’ position the switch is closed and this short-circuits the contact breaker points, which therefore no longer make and break the primary circuit. In the ‘ON’ position the switch is open and the primary circuit is controlled by the action of the contact breaker.

Piston engines of aeroplanes have two independent ignition systems.