Definition
A mixture control position that completely stops the flow of fuel to the engine cylinders, shutting the engine down by starving it of fuel rather than by interrupting ignition. On most piston aircraft engines, it is the full-aft (or fully pulled) position of the mixture control lever.
Plain English
The setting on the mixture control that turns the engine off by cutting off its fuel supply.
Context Anchor
Seen in emergency checklists, shutdown procedures, and engine fire procedures where the pilot must stop fuel feeding the engine.
Derivation
The name describes exactly what it does: at engine 'idle' (low power), this position 'cuts off' the fuel. The phrase entered general aviation use as mixture-controlled carburetors and fuel injection systems became standard, replacing earlier shutdown methods that relied only on switching off the magnetos.
Why Pilots Care
Stops residual fuel from feeding an engine fire after the engine has been shut down.
Intuition Check
Do not read idle cut off as simply a very slow engine setting. In this context, it means the fuel is cut off so the engine stops.
Example Sentence 1
After taxiing to the ramp, the pilot pulled the mixture to idle cut off and the engine shut down smoothly.
Example Sentence 2
Following the engine fire checklist, the pilot set the mixture to idle cut off before securing the fuel pump.