Champion Aerospace: From Denial to Acceptance

Champion Aviation Spark PlugsAccording to the model popularized by Dr. Elisabeth Kübler-Ross in her seminal 1969 book On Death & Dying, there are five stages of grief: denial, anger, bargaining, depression, and acceptance. This is apparently what Champion Aerospace LLC has been going through over the past six years with respect to the widely reported problems with the suppression resistors in its Champion-brand aviation spark plugs. I last discussed this issue in my August 2014 blog post Life on the Trailing Edge.

I first became aware of the Champion spark plug resistor problem in 2010, although there’s evidence that it dates back to 2008. We were seeing numerous cases of Champion spark plugs that were causing bad mag drops, rough running and hard starting even though they looked fine and their electrodes weren’t worn anywhere near the retirement threshold. The thing these spark plugs had in common were that they were all Champion-brand plugs and they all measured very high resistance or even open-circuit when tested with an ohmmeter.

We also saw a number of cases where high-resistance Champion plugs caused serious internal arc-over damage to Slick magnetos (mostly in Cirrus SR20s). If the damaged mag was replaced without replacing the spark plug, the new mag would be damaged in short order. The cause-and-effect relationship was pretty obvious.

In researching this issue, I looked at the magneto troubleshooting guide on the Aircraft Magneto Service website, maintained by mag guru Cliff Orcutt who knows more about aircraft ignition systems than just about anyone I know. Cliff owns and operates my favorite mag specialty shop, and that’s where I send the mags on my own airplane every 500 hours for inspection and tune-up. In reading Cliff’s troubleshooting guide, I came across the following pearls of wisdom:

  • Take an OHM Meter and measure the resistance value from the connection in the bottom of the barrel to the clean center electrode at the firing end, electrode must be bare metal.
  • A new Champion plug will have a value of 800 to 1200 OHMS. New Tempest (formerly Unison-Autolite) will measure 1000 OHMS.  Replace any plug above 5000 OHMS.
  • A spark plug bomb tester can test a bad plug and lead you to conclude it is serviceable. The OHM Meter check is simple, readily available, and amazingly accurate in finding misfiring plugs.

We started asking the maintenance shops we hired to maintain our clients’ aircraft to ohm out the plugs at each 50-hour spark plug maintenance cycle. The number of plugs that measured over 5,000 ohms was eye-opening. Many plugs measured tens or hundreds of thousand ohms, and it wasn’t unusual to find plugs that measured in the megohm range or even totally open-circuit. Here, for example, is a set of 12 Champion plugs removed for cleaning and gapping from a Cirrus SR22 by a shop in South Florida:

Champion spark plug resistance

Notice that only two of these 12 plugs measured less than 5K ohms, and one of those had to be rejected because its nose core insulator was cracked (a separate issue affecting only Champion fine-wire spark plugs, and unrelated to the resistor issue that affected all Champion plugs).

Why spark plugs have resistors

Worn spark plug

A worn-out spark plug.

Early aviation spark plugs didn’t contain resistors. They didn’t last long, either. The reason was that each time the plug fired, a significant quantity of metal was eroded from the electrodes. Magnetos fire alternate spark lugs with alternate polarities, so half of the plugs suffered accelerated erosion of their center electrodes, and the other half suffered erosion of the ground electrodes. Eventually, the ground electrodes became so thin or the center electrode became so elliptical that the plug had to be retired from service.

Spark plug manufacturers found that they could extend the useful life of their plugs by adding an internal resistor to limit the current of the spark that jumps across the electrodes. The higher the resistance, the lower the current. And the lower the current, the less metal eroded from the electrodes and the longer the plug would last before the electrodes got so worn that the plug had to be retired.

Adding a resistor to the plug also raised the minimum firing voltage for a given electrode gap. The result is a hotter, more well-defined spark that improves ignition consistency and reduces cycle-to-cycle variation.

The value of the resistor was fairly critical. If the resistance was too high, the plug would fire weakly, resulting in engine roughness, hard starting, excessive mag drops, and (if the resistance was high enough) arc-over damage to the magneto and/or harness. If the resistance was too low, the plug electrodes would erode at an excessive rate and its useful life would be short. Experimentation showed that a resistance between 1K and 4K ohms turned out to be a good compromise between ignition performance and electrode longevity. Brand new Champion-brand aviation spark plugs typically measure around 1,200 ohms fresh out of the box. New Tempest-brand plugs typically measure about 2,500 ohms. Both of these represent good resistance values right in the sweet spot.


As word of these erratic and wildly out-of-spec resistance values began reaching aircraft owners and mechanics (primarily via the Internet), Champion went on the defensive. At numerous aviation events and IA renewal seminars, Champion reps dismissed the significance of resistance measurements. They explained that the silicon carbide resistor in Champion-brand plugs is made to show the proper resistance whenever a high-voltage pulse is present, and can’t necessarily be measured properly with an ohmmeter. Further, they stated that the proper way to test a spark plug is on a spark plug testing machine (so-called “bomb tester”), and claimed that if a plug functions well during a bomb test, it should function well in the airplane.

Champion old insulator assembly

Champion old insulator assembly.

Of course, this “company line” from Champion didn’t agree with our experience. We’d seen numerous instances of high-resistance Champion plugs that tested fine on the bomb tester but functioned erratically in service. Nor did it agree with the Mil Spec for aviation spark plugs (MIL-S-7886B) which states clearly:

4.7.2 Resistor. Each spark plug shall be checked for stability of internal resistance and contact by measurement of the center wire resistance by the use of a low voltage ohmmeter (8 volts or less). Center wire resistance values of any resistor type spark plug shall be as specified in the manufacturer’s drawings or specifications. 

One enterprising Cessna 421 owner named Max Nerheim performed high-voltage testing of Champion spark plugs, and found that plugs that measure high-resistance or open-circuit with a conventional ohmmeter also had excessive voltage drop when fired with high voltage, and required a higher minimum voltage to produce any spark. Max Nerheim wasn’t just an aircraft owner, mind you, he was also Vice President of Research for TASER International, Inc. and was exceptionally qualified to perform high-voltage testing of Champion spark plugs. Nerheim’s findings flatly contradicted Champion’s company line, and agreed with what we were seeing in the field. Nerheim also disassembled the resistor assemblies of a number of high-resistance Champion plugs and found that the internal resistor “slugs” were failing.


What's your resistance?The spit really hit the fan when Champion’s primary competitor in the aviation spark plug space, Aero Accessories, Inc., launched a marketing campaign to promote sales of its Tempest-brand aviation spark plugs by highlighting the resistance issue. (Aero Accessories acquired the Autolite line of aviation spark plugs from Unison Industries in 2010, an re-branded them under its Tempest brand.) In February 2013, they issued a Tempest Tech Tip titled “The Right Way to Check Spark Plug Resistors,” started selling a fancy spark plug resistance tester, and launched a big “What’s Your Resistance” advertising campaign in the general aviation print media.

Predictably, this provoked a rather hostile response from Champion. Their field reps ratcheted up their public relations campaign claiming that the ohmeter check was meaningless, and insisting that Champion spark plugs didn’t have a resistance problem that affected the performance of their plugs.


In the face of both overwhelming technical evidence from the field that their spark plugs had a resistor problem, and a virtual blitzkrieg from their principal competitor that was starting to erode their dominant market share, Champion began having some self-doubts. Max Nerheim discussed his high-voltage test findings with Kevin Gallagher, Manger of Piston and Airframe at Champion Aerospace, and Gallagher acknowledged that Champion was looking into the issue with the resistor increasing in impedance, but did not have it resolved yet. Meanwhile, the Champion field reps continued to insist to anyone who would listen that claims of resistor problems in Champion spark plugs were false and that the ohmmeter test was meaningless.


Sometime in late 2014, it appears that Champion very quietly changed the internal design of their spark plugs to use a sealed, fired-in resistor element that appears to be quite similar to the design of the Tempest/Autolite plug. They didn’t change any part numbers. So far as I have been able to tell, they didn’t even issue a press release. The Champion Aerospace website makes no mention of any recent design changes or product improvements. But the cutaway diagram of the Champion spark plug now on the website shows the new fired-in resistor. Here are the old and new cutaway diagrams. Compare them and you’l clearly see the difference.

Click on images below to see higher-resolution versions.

Champion spark plug cutaway (old)

Champion spark plug cutaway (old)

Champion spark plug cutaway (new)

Champion spark plug cutaway (new)

I checked with a number of A&P mechanics and they verified that the latest Champion spark plugs they ordered do indeed have the new design. It’s easy to tell whether a given Champion spark plug is of the old or new variety. Simply look at the metal contact located at the bottom of the “cigarette well” on the harness end of the plug. The older-design plugs have a straight screwdriver slot machined into the metal contact, while the newer-design plugs do not.

As I write this, it’s still too early to tell whether Champion’s quiet resistor redesign will cure the drifting resistance problem, but my best guess is that it will. If I’m right, this is very good news indeed for users of Champion aviation spark plugs. I applaud Champion Aerospace for improving its product.

Still, I can’t help but wonder why it took six years for the company to work through its grief from denial to acceptance. I suppose grief is a very personal thing, and everyone deals with it differently.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).


  1. Thanks Mike for the article. I as an A&PIA and business owner have been steering my customers to the Tempest brand because I was throwing away SO many Champion SP! It was ridiculous! Just today I found 3 out of 8 that were bad with the resistance check. I am glad that Champion is finally doing something about it. Hopefully they will take care of the people out there that have spent money on the bad plugs and replace them with the new design.

  2. “wonder why it took six years for the company to work through its grief from denial to acceptance”

    A fear of warranty liability perhaps?

  3. Champion should provide us with good replacement resistors for our perfectly good spark plugs.

  4. Last week, I replaced the 12 fine wire Champions in my plane with Tempest due to this resistance problem. Very hard starting signaled the problem for me. Resistance values were 20,000 ohms or more for some of the plugs. These Champions had just a few hundred hours on them. We’ve asked Champion for replacements. After all, the plugs did cost close to $1200. I hope they’ll honor the request.

    • Hey Mark, a local flyer here was having some trouble with his Comanche running smooth so we started with his SP only to find (1) out of the (12) to be in “serviceable” condition. I tested them first on the Tempest gizmo ( it is fairly quick and accurate) then because of the red light (failing), tested for the Ohms value.They were all very high. He called Champion (BTW these are fine wire plugs too) and they told him to send them in. So he did. They cleaned and replaced all the resistors, replaced a couple plugs that had other defects, turned them around and sent them back to him in a week and free of charge! I was floored! He said that the rep he talked too was VERY nice and accomodating and even stated that “the competition” was killing them so they are trying to regain the market. If you call them to send them in they may replace them all for you.

  5. In April of 2014, I stopped by the Champion booth at Sun & Fun and spoke to the main person there. I shared my findings with him on my 2 year old Champion plugs that I had pulled out of my Mooney, which all showed the high resistance and some internal corrosion. He gave me a contact at the factory and said they would replace them all, which they did without a flinch. I had already swapped out for Tempest plugs after experiencing poor starting problems. I eventually replaced one of my Slick mags to finally clear up the starting problem altogether. After reading your article, I’m suspecting that the defective plugs may have caused my 2 year old mag to fail as well, but I hold little hope that Champion will freely replace or reimburse that item! Is it going to take serious injury or death to convince Champion to completely come clean on this problem?

  6. Thank You Again Mike,

    I have electronic ignition on my Mooney 201, it powers the bottom plugs, regular magneto powered top plugs. The EI powered plugs have shown a much accelerated effect of increased resistance as compared to the mag powered plugs. I ohm test them all at oil change, every 25 hours. I’ll be looking for the new non slotted types.

    Question for you, you mention Champion was in denial for 6 years. You mention you first noticed this in 2008 – what changed in 2008 ? And what was the failure mode of the resistors Mr. Nerheim found ?

    Very Best Regards

  7. I had only one of more than a dozen plugs that tested “good”. The remainder were either cracked or open resistance. On several plugs the resistive element was completely OPEN, meaning the magneto has to arc across the resistor – do a YouTube search for Max Nerheim Champion, and you will see a short video. As a “Motörhead” I often wonder what the perfect spark gap voltage is, well in this case it is about 0.05′ across the spark plug gap and another about 0.5′ gap across the resistor! One very unfortunate scenario could happen if one spark plug is bad (open resistor) and the next in the firing sequence is “good” – the arc could conceivably jump inside the magneto to the next cylinder in the firing sequence! A VERY bad thing!

    Here is the complete write-up I did for Beechtalk:

    If you fly with Champions, I would remove them every oil change, check for cracks and resistance!

    BTW, the problem can not be tested and identified at run-up since the pressure in the combustion chamber is less than during high power climb/cruise and hence require less voltage to arc over, and the air pressure inside the magneto is higher, resulting in higher break over voltages. (Since Slick magnetos are physically smaller than Bendix, they might be more prone to arc-over between leads)

    Thanks Mike for bringing attention to the issue, hopefully it will save someone from getting into serious trouble. Since I wrote the article in Beechtalk I have helped two owners diagnosing rough running engines by simply installing new plugs :).

    Max Nerheim

    • Thanks Max,

      I just bought a box of Tempest plugs from AC Spruce. And e-mailed the link to this article to all my pilot friends.

      Best Regards,

  8. I fly a turbo-normalized Cessna 177RG with the STC’d IO-390. Last fall, during a plug “bomb” test, two of the plugs didn’t pass. These plugs came from cyls 2 and 3, which run hottest in the engine. Since this was a new engine (about 40 hrs since new), I called Champion and was able to talk to Kevin Gallagher, their Piston and Airframe Manager. He mentioned the new design, and said he would overnight a complete new set to me. They followed through and plugs are installed. Also, he sent detailed test reports of the plugs I returned, along with pics of the test process and procedure (the plugs passed on their system). I have flown about 60 hrs on the new plugs now, with no problems. I’ve done a number of lean-of-peak mag checks and all is well. Engine generally starts in 1-2 revolutions hot or cold. So far all looks good. Will do a resistance check at next oil change. Kevin ask that I keep him informed of the performance at 100 hrs, and I will follow through with that.

    Service and response from Champion was excellent. If the solution to the problem was a long time coming, they certainly have recognized that their customers are their best assets. With good performance from the plugs and excellent service from the company, I’ll be buying them going forward.

  9. My mechanic told me about the champion plug problem and I check mine at annual. Most failed the Ohm test. Talking to champion they said they haven’t changed their plugs in over 20 years. Lets see do I want old tech or new tech plugs. My tempest are working great.

  10. I am an A&P mechanic and we do believe that Champion Spark Plug Corp. should compensate for all the trouble they created.

    • You can be sure they will not compensate, but you can get a certain amount of satisfaction by never buying anything from Chanpion again (and recommending the same practice to all of your customers). Social media is so effective.

  11. Mike, can you show pictures of the old and new metal contact you’re talking about for identification purposes?

  12. Since 2008! I had trouble with Champions much earlier than that–in the late 90s, at least. We used to use Auburns, which had that molded-in resistor, amd they lasted forever. Even had a 400-hour warranty. Then Champion bought Auburn (2004, maybe) and shut them down. They should have adopted Auburns design immediately.

  13. Well, I always seem to have a contrary view, so I might as well continue the tradition. I believe that Champion had to change because the Tempest advertising barrage got the herd to scampering. I personally, have run a Cessna 182 from the time the engine was new to TBO (1700 hrs) on the same set of Champion fine wires. I never checked the resistance and never had a miss or a rough moment with the engine (and no mag problems, if that was going to be your next question). On my current airplane (with a Lycoming) the Champion fine wires have over 1000 hours on them. I checked the resistance once, out of curiosity after the Tempest advertising blitz began, and found them all over the place, but the engine didn’t seem to know; always starts and runs perfectly.

    Now then, Champion has been building spark plugs for a while, a long while. They probably don’t know everything, but I bet they know a few things. Probably nothing wrong with the Tempest plugs, I have run some in my other plane, and they also seem fine. But I would not jump to the conclusion that Tempest has discovered some previously unknown secret about spark plugs, except maybe how to sell them.

    • did you happen to have a look at Max’s you tube video ? have a look if you haven’t. i’m a mechanical guy, not a spark chaser, but even i can tell, that aint right. i guess you can say spark plugs are a fault tolerant design. but champion’s quality assurance obviously doesn’t care, nor their management.

      fwiw, i had a problem with my slick ( champion ) magneto as well. about 125 hours after a factory overhaul my Lyc IO-360 was grounded due to rough running. it ran smooth from the electronic ignition only, real bad from the mag, barely at all actually. the magneto points were bad. the moving point is basically a rivet in place on a piece of spring steel. visually, the rivet operation was done obviously wrong. after 125 hours it was quite loose.

      who ever made it didn’t care. who ever inspected it didn’t care. these components have been in production for how many years now ? these groups of people collectively forgot how to make them ?

      it’s obviously their attitude – from the top down.

      • I can only report the data from my airplane operations. How other people maintain and operate their airplanes, I know not. I operated the 182 for 6 years which included 3 years of daily commuting between Olympia and Seattle, on the same set of Champion fine wire plugs and Slick magnetos. I remove plugs at 100 hours to clean the lead out of the bottom plugs, manually, I do not sandblast; I never had to re-gap them. I opened the magnetos at 1000 hours just to see how they were doing; only the carbon block was worn slightly out of limits. My current airplane, a Piper Pacer, is much the same story except I only have 1000 hours on the plugs and mags at this point using the same operation and maintenance practices.

        • understood and my best wishes as well, of course. what i failed to mention here was i ohm check my plugs at oil change and have had to scrap a low time – less than 100 hour – plug driven by the magneto. additionally, the electronic ignition driven plugs all have reduced life. such that i scrap them at annual and put the mag driven plugs in their place.

          i get hot start performance now due to the electronic ignition on my fuel injected Lyc 4 banger. that’s why i had it installed, that’s why i keep it.

          max’s You Tube video is worth watching

          hopefully i’ll get better plug life with the Tempest plugs. i only report my data so that others may benefit from my limited data point. ( and that bad magento point did anger me greatly, since i know how to rivet, it aint rocket science )

        • Steve – Yes, but just because *you* didn’t have problems doesn’t mean a problem isn’t there. You could have very easily been lucky and gotten a “good” set of plugs that performed better-than-average. To draw a recent analogy from the automotive world: A lot of people drove GM cars with faulty ignitions and never had a problem; but that doesn’t mean people weren’t killed and a recall wasn’t necessary.

    • Here’s what I know. I own and fly radial engines for a living. And I’ve had nothing but issues with Chapion spark plugs. No Tempest didn’t in discover anything new, they used a very old design that has been in the BG plugs I run in my Waco. The design has been around for over 60 years, it just cost more to manufacture. I’ve had brand new champions that fail with in a few hours. And it happened regularly, not just to me but to others at my airport. In the DC-3 I fly every day, we have had the same experience and we have quite a few plugs to check to find one that’s bad. Since we switched to Tempest we have not had one plug issue.

    • one set of plugs is not statistically significant. read into the trends and the company behavior…

  14. Gibbles the Wonder Cat

    March 21, 2015 at 3:15 pm

    Another passive aggressive article from a shameless self-promoter.

    Q: What do you call an airplane with Slick magnetos and harness and Champion plugs?

    A: A glider.

  15. I own a flight school… we had far too many problems with Champion plugs. Each time we traced it to high resistance. We switched everything to Tempest, and no troubles. Champion management tried to cover it up by lying… so we won’t be purchasing their plugs again – even with the improved design. Loss of business will hopefully get the Champion leadership fired, sending a message to Corporate America that this behavior is not tolerable.

  16. 1983 Saratoga Turbo, Lycoming TSIO-540-S1AD engine. Engine overhauled in 2012 and new Champion massive plugs on top, fine wires on bottom. First annual, 117 hours, found 1 cracked fine wire and two massives failed the Ohm check, replaced. Last annual, ALL massives failed Ohm check, found another fine wire cracked. Replaced ALL plugs with tempests. Saw an immediate change in the engine operation, faster starting and a really smooth idle. Done with Champion.

  17. I had poor starting and two cylinder had regular fouled plugs in my 2004 C182T. More than half my Champion plugs had internal resistances well over 10K ohms, and after replacing them with tempest plugs these problems vanished. My engine starts first time, every time, and runs much smoother. No plug fouling since then. I have recently replaced all the remaining Champion plugs.

  18. In the last 5-6 years more than 50% of the Champion plugs I’ve tested during annuals have had greater than 5k resistance, many showing open circuits. I have used Aircraft Magneto Service (aka Cliff Orcutt) exclusively for mag rebuilds during the same period and had great results using his mags and 5k testing techniques.

    In the meantime, we’re all stuck with $400+ per engine in defective Champion plugs until we have to come up with spare $ to buy Tempests.

  19. The problem was more pronounced with 1200 series mags. They have more energy which cause the Spark Plug resistor to erode. This can be seen in a Scanning Electron Microscope, little holes in the walls of the resistor,more holes equal more resistence.I sent the SEM pictures to Champion Research they replaced all my plugs!

  20. tunnelportterror .

    April 20, 2015 at 12:15 am

    I just went through this with automotive plugs. I bought (8) Champion RJ12YC on Ebay, and they all measured 100k-300k resistance. the OLD plugs in my car were Autolite 85’s and only measured 4k-5k each. I’m not putting those Champions in anything !! when it comes to resistor plugs the proof is in the measuring

  21. I own a mooney M20F EXE in and I have experimented two engine faillure caused probably for this reason , and have the second with brand new cylinder with about 15 hrs tt ,this is probably scrap at this time

    The temperature have grow up to 750 in about 50 -70 second max
    I send you a picture

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