Definition 1 of 2
Definition
An unwanted continuation of ignition in a turbine engine ignition system caused by residual electrical energy stored in the capacitor of a capacitor-discharge ignition unit, which discharges across the igniter plug after the ignition switch has been turned off, producing a spark when none is intended.
Plain English
A small leftover spark that fires inside the engine after you have switched the ignition off, because the ignition system's capacitor still holds some electrical charge and lets it go through the igniter plug.
Context Anchor
Seen in aircraft ignition system and spark plug discussions, especially during magneto or ignition harness troubleshooting.
Derivation
Capacitance refers to the ability of a component (a capacitor) to store electrical energy. Afterfiring means firing after — in this case, the spark occurring after the ignition has been switched off. Together the term describes a spark caused by stored capacitor energy releasing late.
Why Pilots Care
Prevents proper engine shutdown and may lead to engine damage or fire hazard if not addressed by proper maintenance of ignition leads.
Analogy
It is like a camera flash that gives a tiny extra glow after the main flash because a little stored energy is still draining away.
Grounding Statement
In this term, the “firing” is electrical sparking at the spark plug, not fuel burning in the exhaust.
Intuition Check
Do not confuse capacitance afterfiring with an exhaust afterfire or backfire. This term is about an extra electrical spark at the spark plug after the main spark.
Example Sentence 1
The technician traced the capacitance afterfiring to a faulty bleed resistor in the ignition exciter that was failing to dissipate stored charge after shutdown.
Example Sentence 2
Excessive length of ignition leads can increase capacitance and result in afterfiring during shutdown.