3.2 Aircraft Systems and Flight
Ignition system
Most small aircraft use a direct cranking electric starter system. The systems consist of Magnetos, Spark Plugs, Ignition Switch, Starter and Wires that link the system all together. All these components come together to start the aircraft. Most aircraft have a dual ignition system with two separate magnetos, separate sets of wires, and two spark plugs per cylinder to increase the reliability of the ignition system through redundancy. In other words, it is designed so that if one magneto or spark plug fails, the other remains unaffected and continues to operate normally even with a slight decrease in power. If the Magneto fails during flight, the airplane's rpm will be slightly reduced. In this case, after checking which side of the magneto is the problem, put the switch in the better side. Also we must maintain altitude to maximize its potential glide distance. Futhermore, keep power setting changes to a minimum because engine failures most often occur during major power changes.
A malfunction of the ignition system can be checked through the checklist before takeoff. For example, a system malfunction can be detected by moving the ignition switch from BOTH to RIGHT and moving from BOTH to LEFT. A slight decrease in engine rpm during this check is normal. Acceptable reductions are listed in the AFM or POH of each aircraft. If there is huge rpm reduction or no reduction, then you should suspect the failure. If the engine stops running or the rpm exceeds acceptable limits when switching to one magneto, never fly until the problem is resolved. The cause could be fouled plugs, broken or shorted wires between the magneto and the plugs, or improperly timed firing of the plugs.
An rpm of "no drop" is very unusual, in which case the aircraft should never be flown. Therefore, after stopping the engine, the ignition switch must be turned to the OFF position. Also, even when the battery and master switch are off, the magneto does not require external power, so if the ignition switch is on and the propeller moves even slightly, the airplane may start. Since there is a chance of serious injury in this situation, you should keep an eye on the airplane's propellers to make sure no one touches the airplane's propellers even after the airplane has been powered down.
Failure of the ignition system of an airplane can be scary. Pilot will be even more embarrassed, especially when they are in flight. However, As Mike noted(2020),The beauty of a magneto is its simplicity. When one fails, it's not dramatic, and will not result in a catastrophic engine failure. Also, pre-flight inspections can prevent such accidents in advance. Therefore, we need to conduct more thorough pre-flight checks.
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