Definition
An abnormal combustion event in which the fuel-air mixture ignites in the engine's intake system rather than inside the cylinder, producing a sharp popping or banging sound out the carburetor or induction side. It typically occurs when the mixture is too lean or when ignition timing allows a flame to travel back through an open intake valve.
Plain English
The engine fires in the wrong place — back through the intake instead of inside the cylinder — making a loud pop. It usually means the fuel mixture is off or the timing is wrong.
Context Anchor
Seen in hand propping because a backfire can happen while someone is pulling the propeller through to start the engine by hand.
Derivation
From 'back' (in the reverse direction) plus 'firing' (combustion). The name describes exactly what happens — the fire goes the wrong way, back through the intake instead of forward out the exhaust.
Why Pilots Care
A backfiring propeller can cause serious injury to anyone standing in its path during a manual start.
Intuition Check
Backfiring does not just mean the engine is loud or rough. It means combustion is happening abnormally, often with a sharp pop and possible unexpected propeller movement.
Example Sentence 1
The engine backfired through the carburetor during the start attempt, suggesting the mixture was too lean.
Example Sentence 2
Following the correct hand propping sequence helps reduce the chance of backfiring.