Title: Why Do Aircraft Engines Have Two Spark Plugs Per Cylinder? | Boldmethod
Headings: Why Do Aircraft Engines Have Two Spark Plugs Per Cylinder?
Why Do Aircraft Engines Have Two Spark Plugs Per Cylinder?
1) Reliability
2) More Power
3) Even Combustion
https://www.flickr.com/photos/scsibug/
Spark Plug Fouling
AA1Car.com
Two Really Is Better Than One
Colin Cutler
Images Courtesy:

Content: Depending on your airspeed, it would either slowly windmill as you started descending toward Earth, or it would stop completely. Remember the saying that a propeller is a big fan that keeps pilots cool, and when it stops, pilots start to sweat? There could be some major sweating from that kind of failure. But that's not the only problem. Let's say you had a spark plug stop working in-flight. If you only had one spark plug per cylinder, you would lose more than 25% of your power, if you were flying a 4-cylinder engine. And if you've ever flown a small single-engine plane, you know that a power decrease like that could mean the difference between cruising and not being able to maintain altitude. By having a dual ignition system with two spark plugs, none of this is a problem. If you have a magneto fail, you'll probably see a slight drop in engine RPM, but the other magneto, and the spark plugs that it's connected to, will keep firing on all cylinders. And if you simply have a spark plug fail?