Definition
A mixture-control setting on certain large reciprocating aircraft engines, particularly older radial engines with pressure carburetors, that automatically increases the fuel-to-air ratio as power demand rises. In the Auto Rich position, the carburetor delivers extra fuel during high-power operations such as takeoff and climb to help cool the cylinders and prevent detonation.
Plain English
A setting on the engine's mixture control that lets the carburetor automatically add extra fuel when the engine is working hard, like during takeoff and climb. The extra fuel keeps the engine cooler and protects it from damage.
Context Anchor
Seen on the mixture control, checklist, or operating instructions for aircraft equipped with automatic mixture settings such as Auto Rich and Auto Lean.
Derivation
"Auto" is short for automatic, meaning the adjustment happens on its own. "Rich" describes a fuel-air mixture with a higher proportion of fuel than the chemically ideal ratio. Together the term means the carburetor automatically delivers a richer mixture when the engine needs it.
Why Pilots Care
Protects the engine from overheating and detonation during high-power phases by ensuring adequate fuel cooling.
Intuition Check
Auto Rich does not mean “the richest possible setting” in every situation. It means the system is automatically providing a fuel-heavy mixture appropriate for that operating range.
Example Sentence 1
Before takeoff in the DC-3, the pilot moved the mixture controls to Auto Rich to ensure the engines received extra fuel during the climb.
Example Sentence 2
In cruise the pilot moved out of Auto Rich to a leaner setting once power was reduced.