Definition
Any foreign substance present in a material where it does not belong, reducing the material's purity and often degrading its performance, strength, or chemical behavior. In aviation contexts, impurities are commonly found in fuels, oils, hydraulic fluids, oxygen, metals, and water used in aircraft systems.
Plain English
Something that has gotten into a substance that shouldn't be there. It makes the substance less clean, less pure, and often less reliable.
Context Anchor
Pilots and mechanics encounter this term when checking fuel, oil, hydraulic fluid, air filters, and other aircraft materials that must stay clean to work properly.
Derivation
From the Latin 'impuritas,' meaning uncleanness, built from 'in-' (not) and 'purus' (pure or clean). The aviation usage keeps that original sense: something that makes a clean substance unclean.
Why Pilots Care
Impurities can block fuel lines, damage engines, or cause power loss in flight.
Intuition Check
Do not think of impurity as just a general flaw or poor quality. In aircraft use, it usually means a specific unwanted material mixed into something that should be clean.
Example Sentence 1
Before the first flight of the day, the pilot drained a fuel sample to check for water or other impurities.
Example Sentence 2
Oil with impurities can wear down engine parts faster than clean oil.