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September 07, 2020

Operators of small aircraft such as Cessna planes rely on magnetos to fire airplane’s spark plugs. These vital airplane parts must be regularly inspected and maintained to ensure reliable aircraft operation. Magnetos are one of the oldest aviation components, using a technology that is more than 100 years old, which is why they need regular maintenance. Magneto is a self-contained high-voltage generator, providing ignition to the aircraft engine through spark plugs.

Magneto Purpose

The primary purpose of magnetos is to provide a sufficient amount of electrical power to fire a spark plug at the right time, resulting in igniting the air/fuel mixture in a cylinder. The principle behind its operation involves a rotating magnet that generates an alternating electrical current in a wire coil. Wrapping another wire coil around the primary coil with added turns will dramatically increase voltage. This high voltage (20,000 to 30,000 Volts) in the secondary coil gets directed to the suitable spark plug.

Rotor Function

At the heart of a magneto is a permanent magnet, commonly referred to as the rotor, which gets rotated by a drive present on the engine’s accessory case. It also rotates at the same RPM as the engine on a 4-cylinder engine. However, it spins at 1.5 times the speed of the motor on a 6-cylinder engine. The magnet can retain its magnetic properties for years and be re-magnetized when you open up the magneto for repair or overhaul.

As the rotor begins to lose its magnetic properties, the electric current generated from its spin also diminishes. This leads to a less effective spark and slight engine power loss. That’s why many expert aviation welding technicians emphasize on following the original equipment manufacturer’s OEM recommendations to have magnetos at 500 hours in service inspected or replaced as necessary.

Magnetos Inspections

The standard magnetos check you perform during each pre-takeoff engine run-up will typically reveal only the ignition system’s gross issues. This means that if the difference in RPM drop or the maximum RPM drop between magnetos doesn’t reside within the parameters set by the manufacturer, then you are facing a significant problem that needs to be dealt with pre-flight.

In order to find out even more subtle issues before they become significant flight hazards, it’s highly recommended to conduct a magneto check during flight. This is the time when the ignition system is performing harder under increased stress. You should also install a digital engine monitor, a highly valuable tool that can help you find magneto issues before becoming a significant safety risk.

Magnetos Maintenance

You have to follow a particular magneto maintenance regime as recommended by the manufacturer. This is highly important for both the safety and reliability of the aircraft and its engine. The problem arises when most aircraft operators and some non-experienced aviation mechanics are not fully aware of the great importance of the manufacturer’s guidelines and fail to adhere to the 500 hours inspection benchmark.

Acorn Welding is an experienced aircraft components manufacturer and maintenance specialist based in Canada. Visit our website to learn more about our products and services or contact us for personalized care.