Diving deeper into the world of aviation spark plugs, we will pull back the cowling and affix our inspection mirror to discuss the types commonly used in different aircraft models, insights into their maintenance, and recommendations for their replacement. 

Understanding the Basics

At their core, spark plugs are devices that deliver electric current from an ignition system to the combustion chamber of an engine, igniting the compressed fuel/air mixture by an electric spark. Properly functioning spark plugs are essential for smooth engine operation and optimal performance.

Types of Aviation Spark Plugs

“The two major types of electrodes in today’s spark plugs include the dual nickel alloy massive electrode and the single Iridium fine-wire electrode,” saidAlan Woods, sales manager for piston and power at Champion Aerospace in Liberty, South Carolina. “The nickel alloy electrode design allows for a long-lasting spark plug [300 to 500 hours] at an affordable price. The Iridium fine-wire electrode design offers TBO life [2,000 hours plus] but at a higher cost due to the high cost of Iridium [$4,000 per ounce].”

Massive Electrode Spark Plugs

Massive electrode spark plugs are the most commonly used type in general aviation. They feature large electrodes designed for durability and extended use.

• READ MORE: Intro to Aviation Spark Plugs

Massive electrode plugs are critical features in terms of durability. They can withstand significant wear and tear, making them ideal for aircraft that undergo frequent and long flights. Massive electrode plugs are also cost-effective. They are generally more affordable than their counterparts, the fine-wire spark plugs. Another attribute is their ease of maintenance. Due to their stout construction, massive electrode plugs are easier to clean and maintain.

There are a few downsides to massive electrode plugs. Over time, massive electrode spark plugs can suffer from performance issues due to electrode wear and increased gap size, leading to less efficient combustion. They are also heavier as the larger electrodes add to the weight, which can be a minor concern in aircraft performance calculations.

Fine-Wire Spark Plugs

Fine-wire spark plugs are designed with thinner electrodes, often made of precious metals such as platinum or Iridium, to provide superior performance and longevity.

The fine-wire plug offers improved ignition over massive electrodes, giving the fine-wire electrodes a more concentrated spark and leading to better combustion and engine performance. They also last longer because they are constructed using durable materials, such as platinum and Iridium, reducing the frequency of replacements. Fine-wire plugs are also lighter than massive electrode plugs, contributing to overall aircraft efficiency.

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These enhanced attributes come with a cost. Aircraft fine-wire spark plugs are substantially more expensive than massive electrode spark plugs. They also require careful handling during maintenance to avoid damaging the fine electrodes.

Choosing the Right Spark Plug 

The choice between massive electrode and fine-wire spark plugs often depends on the specific requirements of your aircraft and your flying activity. Massive electrode spark plugs might be more suitable if you fly frequently and cover long distances due to their durability and cost-effectiveness. Fine-wire spark plugs could be the better choice if you prioritize engine performance and are willing to invest in premium parts due to their enhanced ignition efficiency and longevity.

Fine-wire plugs provide a more efficient burn rate and last longer at a much higher purchase price, according to Vince Bechtel, director of aftermarket sales at Tempest Aero Group, which entered the aviation spark plug market in 2010 by acquiring the Autolite brand. A relatively small niche market, the company represents about 10 to 15 percent of the aviation aftermarket. Turbocharged aircraft flying at higher altitudes favor fine-wire plugs, according to Bechtel.

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Maintenance and Replacement Recommendations

Proper maintenance and timely replacement of spark plugs are crucial to avoid engine misfires and ensure smooth operation. Some tips:

●      Regular inspections: Conduct routine inspections every 100 hours of flight time or as your aircraft’s manufacturer recommends. Check for signs of wear, fouling, or damage. Common issues include carbon buildup, oil fouling, and electrode erosion.

●      Cleaning: Use an approved spark plug cleaner to remove carbon deposits and debris. Be cautious with fine-wire spark plugs to avoid damaging the delicate electrodes.

●      Gap checking: Ensure the spark plug gap meets the manufacturer’s specifications. A correct gap is crucial for optimal spark plug performance. Adjust the gap if necessary using appropriate tools.

●      Replacement: Replace spark plugs at the manufacturer’s recommended intervals or if significant wear or damage is observed during inspections. Always use spark plugs that meet the specifications of your aircraft’s engine model.

“Honestly, the biggest issue I see is over-cleaning,” Bechtel said. “Individuals and shops tend to clean plugs until they look brand new out of the packaging. The only thing this does is wear out your electrodes and insulator faster, preventing you from getting the full life out of a set of plugs.”

Troubleshooting Common Spark Plug Issues

Even with regular maintenance, spark plug issues can occur. Some common problems and their potential causes include:

Engine Misfire

• Caused by worn electrodes, incorrect gap, or fouled plugs.
• Solution: Inspect, clean, or replace the spark plugs as needed.

Hard Starting

• Often due to spark plug fouling or improper gap.
• Solution: Check and clean the spark plugs and correct the gap.

Poor Engine Performance

• Can result from degraded spark plugs or incorrect heat range.
• Solution: Verify that you are using the correct type and heat range of spark plugs for your engine.

The introduction of fired-in suppressor seal technology, or FISS, is a recent advancement in aircraft engine spark plugs.

“This technology eliminates the high-voltage silicon resistor, which is prone to resistance value increases over time,” Woods said. “The FISS technology incorporates fired-in conducting and suppressor glasses that establish the resistance value of the spark plug. This means that the end user has a stable resistance value over the entire life of the spark plug. With the introduction of electronic ignition, spark plug designs will evolve with wider gaps to handle the increased energy being produced.”

Understanding the various types of aviation spark plugs and their benefits and limitations can help you make informed decisions about aircraft maintenance. Whether you choose massive electrode spark plugs for their durability and cost-effectiveness or fine-wire spark plugs for their superior performance and longevity, regular maintenance and timely replacements are critical to engine operation. 

Please consult your aircraft’s technical publications and an A&P mechanic to ensure your spark plugs are in an airworthy condition.

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Why Spark Plugs Are Important

This is one area where pilots and airframe and powerplant (A&P) mechanics can find common ground. There is a lot of truth in what “The Boss” sings about. Nothing happens without the spark. The FAA ensures prospective A&P mechanics are well-versed in spark-o-matics.

In the FAA publication, FAA-S-ACS-1 Aviation Mechanic General, Airframe, and Powerplant Airman Certification Standards, the Feds indicate the need for mechanics to possess spark plug theory knowledge. Additionally, prospective A&P mechanics must demonstrate the aptitude needed to remove, clean, and install spark plugs under the skills section. This includes inspecting and checking the gap of spark plugs, and they must identify the correct spark plugs used for replacement installation.

Earlier this year, we discussed the level of aircraft maintenance owner-operators could perform independently. A quick look at the list shows item 20: “Replacing or cleaning spark plugs and setting of spark plug gap clearance.” With great power comes great responsibility. The FAA publishes a fantastic publication entitled FAA Safety Briefing. I ran across an article in the March/April 2010 edition about pilots performing preventative maintenance on spark plugs. A point they make is to be sure not to overtighten the plug inside the engine cylinder, which could cause damage to both the plug and engine. 

Old School Plug Maker

Aviation spark plug manufacturers have produced plugs for almost as long as we’ve had aircraft. Champion Aerospace touts on its historical page that the Wright brothers’ historic first flight “predates Champion’s entry into the aviation industry by only a short time.” Initially, Champion used automotive spark plugs and adapted them for aircraft use. In the 1920s, Champion began the development of spark plugs specifically for the aviation industry. The company continued to improve products throughout the early part of the 20th century.

Here is a fun fact: The Wright Flyer’s engine didn’t have spark plugs. Smithsonian’s National Air and Space Museum diagram of the 1903 Wright Flyer engine mentions that engine ignition came from opening and closing two contact breaker points in the combustion chamber of each cylinder. Four dry-cell batteries provided the spark to start the engine via a coil.

Champion Aerospace, a mainstay for automotive and aviation spark plugs/ignitors, is instantly recognizable by its red, black, and white “bow tie” logo. I have a Champion-branded tool cabinet in my workshop/garage inherited from my dad, who won it in a sales promotion in the 1970s.

Do you recall when I mentioned A&P mechanics needing to identify the correct spark plug for the application? So, how does one achieve such a feat? With manufacturers’ technical publications. Champion posts its Aviation Catalog AV-14 on the interwebs for any and all to use. It is a great resource, and I recommend all aviation professionals download a copy and keep it in their digital toolbox.

New Kids on the Block

For my FLYING print edition readers, you are most likely saying, “What about Tempest Aero Group?” From the rolling hills of North Carolina, Tempest Aero Group is taking aviation by storm, one part and component at a time. In 2010, Tempest acquired Unison Industries’ aviation spark plug, previously marketed under the Autolite brand.

Once Tempest arrived on the scene, it wasted no time making a difference in the aftermarket. I visited the factory in March and saw firsthand the attention to detail that the Tempest team put into each spark plug. Some will say that aerospace manufacturing is slowing in the U.S., but not at Tempest. Each spark plug is made in North Carolina and ready for immediate shipment.

Tempest Aero Group also publishes technical data, including its version of an application guide, and more. I used Tempest plugs at my Part 145 engine shop and they performed well. We never had an ounce of trouble in the decade I owned the shop. Aviation folks are very brand loyal, but at the end of the day, only products that perform will last. As for Autolite Annie, I am afraid she will stay retired. Permanently.

Thanks for tuning in this week for an introduction to aviation spark plugs. We are just getting started, and in the months to follow, I will highlight the different styles of plugs, the care and keeping of aircraft spark plugs, and special tooling you can deploy to keep your ignition system sparking on time. Coming soon, we will discuss the cool things going on over at Electroair with electronic ignition. 

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