Airplane spark plugs foul constantly, primarily because of the large amount of lead in avgas. Many airplane engines (e.g., Lycoming O-360) are already approved

Airplane spark plugs foul constantly, primarily because of the large amount of lead in avgas. Many airplane engines (e.g., Lycoming O-360) are already approved to run on unleaded fuel and have done so for years with vastly improved plug fouling. Additionally, spark ignition engines have redundant plugs (actually, entire ignition systems) to reduce the effect of this issue.