Definition
The small air space between the center electrode and the ground electrode of a spark plug, across which the high-voltage spark jumps to ignite the fuel-air mixture in the engine cylinder. The width of this gap must be set to the manufacturer's specification, as it directly affects spark intensity, ignition reliability, and engine performance.
Plain English
The tiny gap at the tip of a spark plug where the spark actually crosses. It has to be the right size — too wide or too narrow and the spark won't fire the fuel properly.
Context Anchor
Seen in piston-engine ignition system discussions, maintenance inspections, and engine troubleshooting.
Why Pilots Care
An incorrect gap can cause weak or missing sparks, leading to rough running, power loss, or engine failure, especially at high altitudes or during critical phases of flight.
Analogy
It is like the space between two points in a small electrical jump. The space has to be close enough for the spark to cross, but not so close that the spark is weak or poorly formed.
Intuition Check
The word “gap” does not mean a missing part here. It means a carefully set distance that the spark is designed to jump across.
Example Sentence 1
The mechanic checked the spark plug gap with a feeler gauge and adjusted it to the manufacturer's specification before reinstalling the plugs.
Example Sentence 2
A spark plug gap that is too wide may prevent reliable ignition during a high-altitude takeoff.