Definition
In aviation, describing a surface, fluid, or system that has been fouled by a foreign substance which degrades its intended function. A contaminated runway has standing water, slush, snow, or ice on it; contaminated fuel contains water, dirt, microbial growth, or the wrong grade of fuel; a contaminated wing has frost, ice, snow, or other deposits on its lifting surfaces.
Plain English
Something has been fouled by an unwanted substance that makes it unsafe or unreliable to use until it's cleaned, drained, or otherwise dealt with.
Context Anchor
Seen in preflight inspections, fuel checks, runway condition reports, maintenance writeups, and weather-related takeoff or landing decisions.
Derivation
From Latin contaminare, meaning to mix with something unclean or to spoil by contact. The aviation use keeps that core idea: a clean thing has been spoiled by contact with something it shouldn't contain.
Why Pilots Care
Contamination directly increases required runway length, reduces braking, and can cause loss of directional control, especially on takeoff or landing.
Intuition Check
Contaminated does not just mean visibly dirty. In aviation, it means an unwanted substance is present in a way that can affect safety or performance.
Example Sentence 1
After draining the fuel sump, the pilot saw water droplets in the sample and concluded the fuel was contaminated.
Example Sentence 2
Performance charts require longer distances when the runway is contaminated with standing water.