Definition
The presence of any unwanted substance in aircraft fuel, most commonly water, dirt, rust, microbial growth, or fuel of the wrong type or grade. Even small amounts can disrupt engine operation by interfering with combustion or blocking fuel system components.
Plain English
Anything in the fuel that shouldn't be there. Water, dirt, rust, or the wrong kind of fuel can all stop the engine from running properly.
Context Anchor
Pilots look for fuel contamination during preflight fuel checks, after refueling, and any time the aircraft has been sitting where water, dirt, or other unwanted material could get into the tanks.
Derivation
From Latin contaminare, meaning 'to make impure by mixing.' Here it means the fuel has been mixed with something that doesn't belong, even in tiny amounts.
Why Pilots Care
Contaminated fuel can cause engine failure or power loss at any phase of flight.
Grounding Statement
A clean fuel sample should look like the proper fuel and be free of visible water, dirt, or particles.
Intuition Check
Do not assume fuel contamination only means dirty fuel. In aviation, it can also mean water in the fuel, ice, biological growth, or even the wrong fuel type or grade.
Example Sentence 1
During preflight, the pilot drained a sample from each fuel sump and checked for water and debris to rule out fuel contamination.
Example Sentence 2
Improper storage allowed water to enter the tank and create fuel contamination that later caused a rough-running engine.