## What Are They From the [[PHAK Glossary]], a [[Magneto]] is: > `= [[Magento]].definition` The FAA requires the engine ignition to be a separate system from the rest of the electrical system, and magnetos are a great solution. ## How Do They Work Great article from #aopa: https://www.aopa.org/news-and-media/all-news/2019/december/flight-training-magazine/how-it-works-magneto > The magneto is a self-contained generator of high voltage that provides ignition to an engine through spark plugs. A magnet—hence _magneto_—spins in close proximity to a coil of wire. As the magnet spins (or the magnet rotor is turned), it generates a strong magnetic force that is “held back” by a primary coil. The moment the contact points open, a rapid magnetic flow generates a high voltage in the secondary coil, which ignites the spark plug, thus firing the engine. ## How Do We Check Them ### In the Run-Up Again from the article above: > The two magnetos on most GA aircraft—the left and the right—each fire one of two spark plugs on each cylinder. There are two magnetos so that if one fails the engine continues to run, but will be less efficient. So we check them in the run-up by checking the left magneto alone, then the right magneto alone. We expect a drop in RPM each time due to the engine being less effecient. If we don't see a drop, or too much of a drop, we know something is wrong. ### A Grounding Check From another good #Aopa article: https://www.aopa.org/news-and-media/all-news/2002/january/flight-training-magazine/the-magneto-check > In order to understand what you should be looking for while performing the magneto check during the engine runup it's important to understand what the mag switch actually does. The Off position of the magneto switch is different from that of other electrical switches you use. When you switch off the radio, you are removing the electricity from the radio. The Off position of the mag switch does not actually remove electricity from the magneto because the magneto is what makes the electricity. Remember, any time the magnet in a magneto spins, we get electricity. Think about it - if you move the propeller by hand, the magneto is working. > > Turning the mag switch Off actually causes a short circuit (called _grounding_) in the magneto coil that prevents it from working. > > Although the mag switch in your plane only shows one, there are really three Off positions. "Off" means that both mags are grounded and should not be able to power their ignition systems. Remember, grounding only occurs if the P-lead is connected properly. A broken P-lead could cause an engine start if the prop is moved ever so slightly. The grounding check confirms that, while the engine is turning just before shutdown, if you turn Off the magnetos, they are actually grounded correctly and don't continue to fire. If there was an issue, the magneto would fire and the engine would still spin. And you want to know there's a live magneto before you decdie to walk near the propeller! ## Articles From Above, and Additional Resources - https://www.aopa.org/news-and-media/all-news/2019/december/flight-training-magazine/how-it-works-magneto - https://www.aopa.org/news-and-media/all-news/2002/january/flight-training-magazine/the-magneto-check - https://www.aopa.org/news-and-media/all-news/2020/january/flight-training-magazine/ol-how-it-works-p-leads - [[PHAK Ch7]]