Aviation Spark Plug Maintenance
A Hard Knocked life
The Aviation Spark Plug has been with us since the dawn of manned flight and it is likely to be with us for many more years. It’s design and purpose are a core requirement for proper engine combustion. We all know the job the spark plug is tasked with, providing the spark that initiates the burning of fuel in the combustion chamber. we sometimes treat this delicate instrument with very little regard in comparison to other critical parts of an engine’s ignition system. Using proper maintenance practices and a little patience will ensure you get maximum longevity out of your plugs.
There are currently two types of spark plugs available for general aviation piston engines, The most common; massive electrode “E” type and the iridium (fine-wire) “S” type plugs. Both of which have their pro’s and con’s.
Spark Plugs by their nature are consumables, meaning they are life-limited components. They will eventually “wear out” and need replacing. The typical massive electrode spark plug will last on average about 300-500 hours in lower compression engines. I have seen reports from operators that aircraft equipped with Iridium plugs are getting around 1200+ hours of life from their plugs. That is a huge increase in utility by using iridium plugs. In addition to the increase in plug life, fuel burn is typically reduced by 1-2 percent, easier starts, so why would you even ponder the idea of not using iridium plugs? The short answer is: Price. Many times, the cost of one plug will cover a whole set of “E” type plugs.
Regular servicing is essential to maximizing plug life. Servicing plugs include tasks like checking and setting the proper gap, checking the resistance, rotating, and of course cleaning. Depending on how often an aircraft flies, a once a year plug cleaning during the annual inspection is not sufficient to ensure the plugs last to their effective service life. I have found that 100 hours of flight time or every other oil change is a reasonable schedule to have your plugs serviced and inspected.
Other issues with plugs, besides the normal checks during servicing, that I have been finding is corrosion. Over time the barrel of a plug will lose its nice shine and darken, this is normal and no reason for rejection. However, when layers of metal start to flake off the barrel then it becomes an issue. Another issue is damage due to misuse: Dents in the barrel, damage to the threads, Cracked or broken ceramic insulators, depending on the severity, all of these defects can be cause for rejecting a plug for service. If you ever drop a spark plug, no matter the height it fell, consider it damaged and take the plug out of service.
There are many techniques to ensure you get the most value and utility from your Aviation Spark Plugs. Ensure you read service bulletins and recommended procedures from your plug manufacturer. With these few tips, your Aviation Spark plugs should give you hundreds of hours of service.
