We know that dual means simply two or maybe some type of a binary system but why do modern aircrafts have a Dual Ignition system. A Dual Ignition is simply two Magneto Systems (electrical generators) supplying a continuous alternating current to the two spark plugs in particular cylinders. So, specifically each cylinder has two spark plugs with each having its own electrical current and the ignition having four positions.

The Main Role of the Dual System

The beauty of having a dual system and four positions is simply safety and having other areas to fall back on in order to land when other systems might fail. This allows for the pilot to use another switch or a position long enough to get the plane safely to the runway.

Let us take a look at the separate positions:

  • L- R- in either the “L” or “R” position one magneto is working and only one set of spark plugs are being used to ignite the cylinders.
  • Both- This is when both sets of spark plugs are firing and being used.

What Does An Ignition System Do?

The ignition system is separate from the electrical unit in that it only needs a boost from the battery that operates a series of gears and gets the crankshaft rotating to start the ignition process. Once the fuel in the cylinders are sparked by the ignition system then the continuous current is provided by an engine system and the battery is no longer needed and turned off.

Importance of Aircraft Spark Plugs

Once you dive into what we stated above then you will start to understand the secondary effects of a malfunctioning spark plug. This is simply why there are four spark plugs all together and four separate positions to minimize any problems and have a safety net. At worse case scenario, a spark plug that has decided to not provide current will result in loss of engine power or even loss of life.

Maintenance of Spark Plugs

The spark plug has one responsibility and needs to do it right. It provides a current between the gaps of the core and ground electrodes to ignite fuel in the cylinders. Over time this gap will change shape because of the electrodes being ionized and the gap changes its structure. If the gap is somehow too narrow or large then it might misfire and not work. This is why maintaining the spark plug every 100 hours is a necessity.

Choosing the Right Spark Plug

Aircraft Spark plugs need to meet specific engine and aircraft requirements for thread size, reach, heat rating, shielding, and terminal connection. With extreme heat going to 1200 degrees F at the electrode tip and lead being used in the aircraft fuel; It is no surprise that the electrodes of a spark plug are under constant resistance and need proper attention. An iridium spark plug is known to resist lead better and will ultimately last longer due to the fact that iridium is the hardest wire available for a spark plug.


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