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How to destroy your engine in one minute

At least once a year for as long as I can remember, I have been contacted by an aircraft owner whose piston aircraft engine was destroyed or severely damaged by a destructive detonation or pre-ignition event. In one recent 12-month period, I encountered three such incidents.

One incident involved British Cirrus SR-20 powered by a 200 horsepower Continental IO-360-ES engine. The plane was equipped with an Avidyne Entegra MFD with an integrated engine monitoring system called “EMAX.”

The CHT data downloaded from the EMAX system tells the short story of this engine’s demise:

SR-20 pre-ignition event

Click on image to open a higher-resolution version.

Everything looked fine until about two minutes after the pilot applied takeoff power, at which point the #1 cylinder’s CHT began to climb rapidly compared to the other five cylinders. At the three-minute mark after brake release—with the aircraft at roughly 2,000’ AGL—CHT #1 rose above 400°F and set off a high-CHT alarm on the MFD.

CHT #1 continued its rapid rise—nearly 1°F per second—that continued unabated until the piston and cylinder head were destroyed approximately five minutes after takeoff power was applied and two minutes after the CHT alarm was displayed. At that point, since the cylinder was no longer capable of combustion, CHT #1 started plummeting.

We can’t be sure just how hot CHT #1 got because the Avidyne EMAX system “pegs” at 500°F. A reasonable guess is that the CHT peaked somewhere between 550°F and 600°F. No cylinder or piston can tolerate such conditions for very long, and this one obviously didn’t.

Aftermath

Not long after CHT #1 went off-scale on the MFD, the pilot realized something was very wrong, and pulled the power way back. But he was a couple of minutes late, and the engine was already toast. Here’s what the #1 piston looked like after the event:

Piston with corner melting

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Note the melted corners of the piston crown, the destruction of the top compression ring lands, and the severe metal erosion above the piston pin. (Much of this molten metal wound up inside the crankcase and contaminated the bearings and oil passages.) Also note the severely hammered appearance of the piston crown, the classic signature of heavy detonation. The cylinder head was found to have a big chunk of metal missing from it. Both spark plugs were destroyed by the event as well.

This engine was a low-time Continental factory engine, so the owner figured that the severe engine damage would be covered under Continental’s warranty. I advised him not to bother filing a warranty claim, because I’ve never known Continental to give warranty consideration for a destructive detonation or pre-ignition event. Continental considers this to be operational abuse, not a defect in materials or workmanship, and therefore not covered by warranty. (For what it’s worth, I agree with Continental’s position on this.) The owner didn’t believe me and filed a warranty claim anyway. Continental promptly and unequivocally denied the claim, just as I predicted.

The moral of the story is that it is important for aircraft owners to have a good digital engine monitor installed, to know the telltale symptoms of destructive detonation and pre-ignition, and to act fast when those symptoms appear. You may have less than one minute to react if you want to save your engine.

Another incident

Here’s another similar case that occurred to a Beech Bonanza very shortly after takeoff. The annotated JPI data for this event is courtesy of General Aviation Modifications Inc. (GAMI):

Preignition event

Click on image for a higher-resolution version.

This time, it was the #5 cylinder that experienced thermal runaway and pre-ignition. It was an even more severe event than the one suffered by the Cirrus, and took only two minutes from the application of takeoff power to the complete destruction of the #5 piston, which wound up with a large hole melted through the piston crown:

Holed Piston

Click on image for a higher-resolution version.

Now that’s ugly!

In yet another case (for which I unfortunately have no photos), a drop-dead gorgeous Lancair IV-P kitplane powered by a fire-breathing 350-hp TCM TSIO-550 engine went up for its first test flight after 10 years of laborious building time by the owner. Within minutes, the airplane was back on the ground with an engine that was totally destroyed. A forensic post-flight evaluation revealed that the magnetos had been timed approximately 10 degrees advanced from the proper timing. That turned out to be a $50,000 mistake.

The Lancair’s instrument panel was wall-to-wall glass, including an ultra-sophisticated digital engine monitoring system. The engine monitor was literally crying out for attention throughout the short test flight, but the test pilot never noticed its warnings until the engine cratered.

What causes this?

There are a number of things that can cause or contribute destructive events like these. I’ve already mentioned one: advanced ignition timing. It’s astonishing how often we see engines with the magneto timing advanced several degrees from spec. (E.g., 25° BTDC when the engine data plate calls for 22° BTDC.) Even a couple of degrees is enough to significantly reduce the detonation margin of the engine. Add a hot day and perhaps a cooling baffle that isn’t quite up to snuff, and BOOM!

Owners should be particularly alert for mis-timed magnetos whenever maintenance is done that involves magneto removal or adjusting magneto timing. (More often than not, these occur during the annual inspection.) If mag timing is advanced, you’ll notice that your EGTs are lower and your CHTs are higher than what you were seeing prior to maintenance. (Retarded timing results in the opposite: higher EGTs and lower CHTs.) If you notice this after the airplane comes out of maintenance, take it back to the shop and have the mag timing re-checked. It’s a quick check and could save your engine (not to mention your gluteus maximus). Magnetos are required to be timed within one degree of the timing specified on the engine’s data plate, and any error should be in the retarded direction.

MP and FF guage comboAnother common culprit is inadequate fuel flow on takeoff. When taking off from a near-sea-level airport—or from any elevation if you’re flying a turbocharged airplane—you need to see fuel flow that’s right up against the red-line on the gauge (or the maximum fuel flow shown in the POH). Unlike most other gauges on your panel, hitting red-line on the fuel-flow gauge (or even going a smidgen over) is a good thing, not a bad thing. Takeoff fuel flow is a lot like tire pressure—a bit too much is a whole lot better than a bit too little. Anything less than red-line fuel flow on takeoff reduces the engine’s detonation margin, and significantly less can reduce it enough to cause a catastrophic event.

Not long ago, a client of my maintenance-management firm had a prop-strike incident that required a teardown inspection of the engine. When the inspection was complete and the engine was reinstalled in the airplane, the owner picked up the airplane from the engine shop and flew it back to his home base airport. Upon arriving there, he informed us that the fuel flow was 3 GPH below red-line on takeoff, and asked that we schedule a service appointment to have the fuel flow adjusted.

I was flabbergasted. What was this owner thinking? Why didn’t he abort the takeoff immediately when he noticed that the fuel flow was 3 GPH short, and ask the engine shop to adjust it? Why would he fly the airplane home in that condition? What part of “inadequate detonation margin” didn’t he understand?

Yet another cause is a partially clogged fuel injector nozzle. This can occur anytime, but most frequently occurs shortly after the aircraft comes out of maintenance because that’s the most likely time for foreign material to get into the fuel system. (I’ve had two serious clogged-nozzle episodes in my airplane over the past 25 years, and both occurred shortly after an annual inspection.)

Save your engine!

ThrottleRegardless of the cause, the solution is not rocket science. There are two simple rules that will almost always prevent these sorts of destructive events from occurring:

First, check your fuel flow gauge early on every takeoff roll. If the fuel flow is not at red-line or very close to it, reject the takeoff and sort things out on the ground. (The exception is takeoffs at high density altitudes in normally-aspirated airplanes, and detonation is quite unlikely under those conditions.)

Second, set your engine monitor CHT alarm to 400°F or less for Continental engines and 420°F or less for Lycoming engines. (On my own Continental-powered airplane, I have my alarm set to 390°F.) When the alarm goes off, do whatever it takes right now to bring the CHT back down below 400°F. Verify that the mixture is full-rich. Turn on the boost pump if it isn’t already on. Open the cowl flaps if you have them. And if CHT triggers the alarm and appears to be rising rapidly, throttle back aggressively to stop the thermal runaway. Don’t be shy about doing these things immediately, because you may only have a minute or two to act before your engine craters.

(Oh, and if your airplane isn’t equipped with a digital engine monitor with CHT alarm capability, do yourself a favor and install one. Trust me, it’ll pay for itself quickly.)

When you get on the ground, put the airplane in the shop and have the spark plugs removed and inspected for damage, the cylinders borescoped, and the magneto timing checked. If takeoff fuel flow was short of red-line, have it adjusted before further flight.

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 Amazon.com 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 Amazon.com in paperback and Kindle versions. (508 pages).

27 Comments

  1. Mike, it would be helpful if you could guess the cause & earliest possible visibilities of each of the problems. (Would early warning for #2 have simply been the EGT rise during runup?)

    • The cause is very difficult to guess because these violent pre-ignition events almost always destroy the evidence.

      You are discerning in noticing that the second incident, the #5 cylinder was exhibiting anomalous EGT indications during runup and a really sharp pilot would have noticed this and either decided not to take off with the known deficiency or at least been spring-loaded to abort the takeoff if CHT #5 ran away. So far as I can tell, the first incident provided no advanced warning to the pilot prior to his application of full takeoff power.

      • Mike,
        Great article. The 1 and 3 cylinders on my Lycoming O-360 run hot (400 – 415) on climb out. When at level flight they are normal at 350-370. Checked the baffles and intake manifold, all ok. You mention a higher limit for a Lycoming to be 420. Should I be concerned about a 415 on climb out?

        • Im no expert like mike, just a young a&p but I would have your intake looked over and maybe just replace the intake seals and hoses on that side if they are getting hard and crispy and your baffling seals good. It doesn’t take much of a leak to really lean a cyl out at high power settings. Pretty easy to do too on most installs.

        • My 0-360 also does this, and always has. It is a high time engine w/ high time cylinders and the #3 has paid the price twice over. I think it is because the oil cooler steals cooling air from #3, though I blocked it off one winter as a test and the temp did not go down significantly. #1 is not really a problem. At Mike’s suggestion I add carb heat in flight and it helps equalize all the temps.

  2. Although I agree that an engine monitor is a good thing, recognizing the symptoms and taking action
    “You may have less than one minute to react if you want to save your engine.”
    in that time frame maybe beyond most of many pilots proficiency. At 2000 feet on take off there a lot of other factors being attended to. Not sure many people would notice this or react in time.

    • I agree that most pilots would not notice the CHT runaway UNLESS their engine monitor was programmed to alarm whenever CHT exceeded 400F or so. That’s why I believe that user-programmable CHT alarms are an absolutely must-have feature in engine monitors.

      • I have had my JPI700 mounted in 2 positions, initially out of the way on the RHS of the panel. Much later decided to bring into easy view of my scan when upgraded avionics. Now it is not possible to miss the flashing display. With familiarisation you will notice such an anomaly very quickly. We do all regularly scan the panel don’t we? I feel a sense of apprehension whenever I fly aircraft without one.

      • Mike, would you not see the high CHT on the run up check for the aircraft before take off? It makes sense to be able to view the engine condition from the default aircraft CHT gauges.

    • Just a suggestion…safely incorporate your engine monitor – specifically CHT readouts – into your panel scan, not only on take off but also during cruise and descent. It can save a multi-thousand dollar headache later on.

  3. When I was training for my license 46 years ago, we were flying aircraft with exactly the same engine configuration as we use today. In the meantime we got access to the most advanced avionics like GPS, terrain warning, computer generated terrain and self-righting autopilots.
    Despite that, we are still working with mechanical magneto’s with upgraded toy springs in it.
    Why do we still not have electronic ignition (with redundancy and self powered) and engine management available for these engines, which by the way in itself are very dependable platforms.
    Yes, there are some of these improvements available for the experimental market, but you cannot use them on a certified aircraft. In my opinion the outdated regulation, while very appropriate at the time, now holds back necessary safety improvements. Nowadays a pilot should not have to worry about an engine, it should simply work just like the one in your car, so that a pilot can concentrate on flying safely in the present much busier airspace.

  4. In your other articles you’re adamant about keeping CHTs below 400deg. but here you indicate up to 420 for Lycs? Without looking at my engine manual I’m unclear on what it says but can you explain or point to an article for why the difference?

  5. You talk about a fuel flow gauge. I have a PA 28-236 which does not have a fuel flow gauge.
    I do have a EDM 700 but even in the fuel flow area it takes time to cycle to the fuel flow.
    The POH does not have the maximum fuel flow.
    What’s the answer.

  6. Hmmmmmm so Mac thinks we all need multi function digital engine management systems in order to keep from trashing an engine due to pre ignition/detonation and how does he sell this idea that a $5-6k investment in instrumentation is a good idea? By giving us examples of three engines destroyed in that way ALL OF WHICH WERR EQUIPPED WITH SUCH AN ENGINE MANAGEMENT SYSTEM! Am I missing something here?

    • The fact is we are pilots, not flight engineers. Most of us have neither the time nor the inclination to learn every nuance of engine management and then watch the gauges like a hawk. It is time for GA engines to move out of the Dark Ages.

      • Well, the “test pilot” of that Lancair sure should have noticed…

        • Correct and even with the fancy super expensive glass cockpit engine monitor it really did not help. Of course the pilot should have paid attention or perhaps it was a glass cockpit system failure?

      • True but dropping 10-15K on a new engine computer instead of saving the cash and using the default aircraft instruments is more frugal as we don’t all have open pocketbooks in this day and age.

        • Ben, I can see that cost is part of your argument not to install an engine monitor system. But this is not a cost is an investment. An investment in safety, just like one decision to buy a car with front and side airbags, Of course the car will cost more but most of us wouldn’t buy a car without these safety devices.

    • You also need to pay attention to what’s going on. My new engine monitor is located to the right of the radio stack with an annunciator just to the left of the PFD where it is easily visible. The monitor I replaced also had an alarm function, but it was poorly located (my fault) so when the alarm flashed, it could easily be overlooked.

    • That’s a fair point. Though consider that it was only possible to describe these events in the article on those engines _because_ they had engine monitoring data to draw upon. There is no shortage of engine failures on less-instrumented engines, but you get no pretty timelines for post-facto analysis (and of course even less of a chance of detection at the time).

  7. Aircrafts piston engines are way behind technology compared to the automotive world. When I had my intro flight 2 years ago in a 172C, I was stunt that after start up I had to check both magnetos to make sure they were both up, and check the temps at the run-up. And of course the timing has to be right on. I had to check the timing on my Honda motorcycle regularly, when I was 17 years old. I’m now 63, and I can’t believe that aircrafts piston engines are still destroyed because of that ancient technology!

    • If you think progress in aviation is too slow, you can always picket your MIDO.
      Let me know how that works for you. 😉

  8. As always, great advice. For those with older aircraft and stone-age (or no) engine monitoring, paying attention is possibly of even greater importance. ANY weirdness on mag check, any fall-off of power, strange noises, or unusual or fast-changing temperatures — even if all you have is oil temp — are causes for immediate attention. (True, using only oil temperature would be too slow to catch detonation or pre-ignition, but these events don’t often occur spontaneously; they are almost always caused by someone’s touching something.)

    General rule: anything that is sudden is usually something bad.

    Funny noises while taxiing or on runup are God’s way of telling you to have a look at something. Don’t wait until they get louder, funnier, or (dread!) completely quiet in the air.

  9. These PRE-IGNITION failures are usually caused by dropped spark plugs or spark plugs that have cracked as a result of plenty of detonation (usually turbo engines mismanaged). Yes these failures are captured by engine monitors. But the pilots were all literally “Dogs Watching TV” (I have a copyright on that saying for untrained pilots :-0)

    So in all seriousness, and Mike himself regularly endorses APS, and has attended several times himself…..for your educations sake, for your engine and wallets sake….or for yours/family sake, attend the Advanced Pilot Seminars engine management made easy course. This is available in Ada OK USA and Brisbane Australia.

    Mike…I hope you don’t mind me plugging the course over there!
    Best Regards
    David Brown
    APS-Aust.

  10. So Mike, what is wrong with the standard aircraft gauges for CHT, EGT, and so forth for monitoring engine health? Do you really need to drop 10K on a new engine computer when these already come with the aircraft and do the same thing? Seems like an expensive waste of money in my opinion for a pilot without an open pocketbook.

  11. Bill Wightman

    May 9, 2015 at 8:17 pm

    Yeah, you’re missing the whole point. Mac is making the case that we need to check a few things shortly after takeoff. The fact these aircraft had installed monitors doesn’t help if the pilot isn’t going to look at them – an unfortunate fact that was pointed out in every case. Mac wrote this article in the hope that we’d take a little of his wisdom to heart and change our flying habits for the better.

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