Definition
A threaded metal sleeve installed in the spark plug hole of an aircraft engine cylinder head, providing a wear-resistant, replaceable seat into which the spark plug is screwed. The bushing protects the relatively soft aluminum cylinder head from thread damage caused by repeated spark plug removal and installation.
Plain English
A small metal sleeve threaded into the cylinder head that the spark plug screws into. It protects the cylinder threads so the spark plug can be removed and replaced many times without wearing out the engine.
Context Anchor
Seen in engine maintenance, spark plug replacement, cylinder repair, and aircraft maintenance records.
Derivation
A 'bushing' in mechanical use means a sleeve that lines a hole to protect it or fit a part inside it. The word comes from the Dutch 'bus' meaning a box or sleeve. Here it's a sleeve that lines the spark plug hole.
Why Pilots Care
A damaged bushing can cause spark plug loosening, compression loss, or overheating, directly affecting engine reliability and safety.
Analogy
It works like a threaded insert in soft wood that lets you screw and unscrew a bolt many times without stripping the original material.
Intuition Check
Do not think of the spark plug bushing as the spark plug itself. It is the threaded sleeve in the cylinder head that the spark plug screws into.
Example Sentence 1
During the cylinder inspection, the mechanic found a damaged spark plug bushing and replaced it before installing the new plug.
Example Sentence 2
The technician installed a new spark plug bushing before torquing the plug to the correct specification.