How are the ignition system spark plugs arranged in the C172S engine?

In the Cessna 172S engine, the ignition system employs a dual ignition system featuring two spark plugs for each cylinder. This design enhances reliability and efficiency. With two spark plugs connected to two separate magnetos, if one magneto fails, the other can still provide ignition for the engine, ensuring continued operation and improving safety.

Additionally, having two spark plugs per cylinder promotes more complete combustion of the fuel-air mixture, leading to better engine performance, reduced engine roughness, and improved starting capabilities. This redundancy is a standard feature in many general aviation aircraft to mitigate the risks associated with engine failures.