What is the engine starting process in a Cessna 172?

The engine starting process in a Cessna 172 involves engaging the starter with boosted power from the impulse coupling. The impulse coupling is a feature typically found in some aircraft magnetos, which provides an initial boost of rotational energy to help start the engine. When the starter is engaged, the impulse coupling helps to generate a higher voltage for the spark plugs at low RPMs, which is crucial in ensuring a reliable ignition of the fuel-air mixture in the engine cylinders.

This method takes advantage of the mechanical design of the impulse coupling to aid in starting the engine, making it more efficient and effective than relying solely on other methods, such as simply turning on the fuel pump or manually engaging the starter without the boost from the impulse coupling. Additionally, running the auxiliary pump does not directly contribute to the initial spark required for engine starting and is generally used to ensure fuel delivery rather than to initiate combustion.