The engine has several systems which support its operation.
Ignition System
The ignition system provides the spark plugs with electricity to fire. The engine drives two magnetos, which are small electric generators dedicated to powering the spark plugs. They continuously power the spark plugs anytime the engine is turning. This design allows a running engine to continue to run, even with a complete electrical system failure. Each magneto is capable of operating the engine alone. Two are installed for redundancy.
Similarly, two spark plugs are installed in each engine cylinder, instead of one. The two magnetos are referred to as the left and right, each firing its own set of spark plugs. If any one spark plug should fail, it’s cylinder should continue to operate on the remaining spark plug. If either magneto should fail, the other magneto will still power its set of spark plugs. As a result, it would take multiple failures in the ignition system to seriously degrade engine performance and cause engine failure.
Because of this redundancy, the failure of an individual component may go unnoticed by the pilot. It is important to conduct a preflight check of the airplane’s ignition system in accordance with the procedures recommended by the manufacturer.
In addition to redundancy, the use of a dual ignition system also provides for improved engine performance under normal circumstances, since the two spark plugs provide for a better burn of the fuel/air mixture inside the engine.
Ignition System Operation
The ignition switch on a small airplane is operated by turning a key. The switch positions are off, left, right, both, and start. When the switch is in the off position, the ignition system is set to not power the spark plugs. If the propeller is turned with the switch set to the off position, the magnetos still generate electricity, since they generate electricity anytime the engine is turning. However, this electricity is routed through the switch and into the airplane’s airframe, preventing it from firing the spark plugs. If the switch or its wiring is damaged, it could result in the spark plugs firing even with the switch in the off position. When the left magneto is selected, the right magneto is turned off by grounding it to the airframe. Similarly, if the right magneto is selected, the left magneto is prevented from firing its set of spark plugs. In the both position, both magnetos are permitted to fire their respective spark plugs. The start position allows the airplane’s battery to power the electric starter.
Oil System
The engine must be lubricated to operate. The oil system on the airplane provides a clean oil supply to the engine. It incorporates an engine driven oil pump and an oil filter. Most general aviation engines are of the wet sump design, in which the engine oil remains inside the engine case. In a dry sump system, the oil is stored in a separate oil tank, away from the engine block.
After starting the engine, the oil pressure gauge should be checked to verify the engine is being lubricated properly. Takeoff should not be performed if the oil pressure indication is not in the normal range, since the engine will fail without proper lubrication. Unlike other engine failures, when an engine dies from being ran without oil, it is not going to restart. The oil pressure gauge should be scanned anytime the engine is running.
Aviation engines are air cooled externally, but reciprocating aircraft engines are dependent on the circulation of lubricating oil for internal cooling. Always ensure sufficient oil quantity, since lower oil quantities will result in the engine running hot.
Your first action after engine start should be to check for unintentional movement of the aircraft and set power to the recommended warm-up rpm. Then, check the oil pressure to determine that the oil system is functioning properly at recommended levels within the manufacturers time limit.
An oil temperature gauge is also provided to the pilot. In contrast to the oil pressure, which should come up immediately after and even during the engine start, the oil temperature may take several minutes to come up, especially in cold weather.
Fuel Pump
An engine driven fuel pump assures that fuel is provided to the engine when the engine is turning.
Low wing airplanes usually have an electrically powered fuel pump which aids the engine driven fuel pump. This auxiliary or "boost" pump is used for engine starting or in the event of engine driven fuel pump failure.
High wing airplanes may utilize a gravity feed system to aid the engine driven fuel pump. They may or may not have an auxiliary electric fuel pump installed.
Generator/Alternator
Driven by the engine, the generator or alternator provides electrical power to the airplane's electrical system. A generator creates a flow of direct current (DC) electricity, while an alternator produces alternating current (AC). Alternators are commonly used, as they provide more consistent electrical power as the engine power varies. >
Vacuum Pump
An engine driven vacuum pump supplies suction, required for the operation of several flight instruments.
Other Accessories
While these systems are typical of small training airplanes, systems vary between manufactures. Other engine systems and accessories may be installed, depending on the airplane.