Definition
An aircraft spark plug containing a built-in resistor element in the center electrode circuit, designed to suppress radio interference and reduce electrode erosion by limiting the current that flows during the spark discharge.
Plain English
A spark plug with a small resistor inside it. The resistor cuts down on the electrical noise the spark makes and helps the plug last longer by softening the spark.
Context Anchor
Seen in aircraft engine ignition system maintenance, spark plug selection, and troubleshooting rough engine operation or radio static caused by ignition noise.
Derivation
Resistor comes from the Latin resistere, meaning to stand against or hold back. In this plug, the resistor holds back some of the electrical current at the moment of spark, which both quiets the radio interference and reduces wear on the electrodes.
Why Pilots Care
Unsuppressed spark plugs can create radio noise that interferes with ATC communications and navigation signals.
Intuition Check
Do not read “resistor” as meaning the plug blocks the spark. The resistor reduces unwanted electrical noise; the plug still has to make a strong spark in the cylinder.
Example Sentence 1
The mechanic installed resistor spark plugs to help quiet the ignition noise the pilot was hearing on the radios.
Example Sentence 2
During the annual inspection, the technician checked that all resistor spark plugs were within resistance specifications.