Aircraft Ignition System

 The ignition system consists of magnetos, spark plugs, high tension leads, and the ignition switch. The magnetos are not attached to the electrical system in the aircraft, instead, it uses a magnet to create an electric current that will ignite the spark plugs, as long as the crankshaft is moving.  Most aircraft have two magnetos that work independently of each other. Each magneto is connected to one of the two sparkplugs in each cylinder. Having two sparkplugs as opposed to one assist in the combustion process with the fuel-air mixture.

There are a few things that could go wrong with the ignition system. The magneto could go out, there could be a problem with the wire that connects the magneto to the sparkplug or the spark plug could be firing improperly. This could impact the engine power output. The good news is that since there are two magnetos and two spark plugs per cylinder if one side fails during flight you can still rely on the other side. Despite this, if you know that one side is not functioning properly you should not fly until the malfunction is fixed. One way that you can check to ensure that everything is working properly is by testing the ignition switch. The switch has five settings; off, right, left, both, and start. In order to test this system before flight, you have to monitor the RPMs while you manipulate the ignition switch. You will move the switch from both to left, back to both, and then to right. While doing this the RPMs will change a little, but you are looking for drastic changes or differences in the left vs the right.

It is also important to remember to turn the ignition switch to the off position before you depart the aircraft because if left on and the propeller is moved at all it could start the engine. Even if the ignition switch is turned off, if there is a problem with the wire that connects the ignition switch to the magneto, and someone moves the propeller the engine could turn on.

 

Federal Aviation Administration (FAA). (2016). Pilot’s Handbook of Aeronautical Knowledge (PHAK). Retrieved https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/

 

Shi, Xudong, et al. “Fault Diagnosis Method Research of Aircraft Ignition System Based on Waveform Image Matching.” Procedia Engineering, vol. 15, 2011, pp. 2527–2532., https://doi.org/10.1016/j.proeng.2011.08.475. Accessed 30 Jan. 2022.