Definition
A reciprocating engine condition in which an excessive amount of fuel has entered the cylinders, intake manifold, or carburetor, producing a fuel-air mixture too rich to ignite. A flooded engine will not start until the excess fuel is cleared, typically by opening the throttle fully, closing the mixture control to idle cutoff, and cranking the engine to draw air through and lean out the mixture.
Plain English
Too much fuel has gotten into the engine, so the mixture is too wet to burn. The engine will not start until the extra fuel is cleared out.
Context Anchor
Most often encountered during engine start, especially after too much priming or repeated unsuccessful start attempts.
Derivation
The word 'flooded' comes from the image of something being overwhelmed by liquid. Here, the cylinders have been overwhelmed by liquid fuel, leaving no room for the proper amount of air to support combustion.
Why Pilots Care
A flooded engine wastes time and battery power; incorrect clearing procedures can also create a fire hazard from unburned fuel exiting the exhaust.
Intuition Check
Flooded does not mean the engine has water in it. Here it means the engine has too much fuel in the starting process.
Example Sentence 1
After three failed start attempts with the primer, the pilot suspected a flooded engine and ran the recommended clearing procedure before trying again.
Example Sentence 2
Clearing a flooded engine requires turning off the fuel and magnetos, opening the throttle, and motoring the engine to expel the excess fuel.