Definition
Substances on a runway surface — such as standing water, slush, snow, ice, rubber deposits, sand, or oil — that reduce tire-to-surface friction and degrade braking and directional control performance during takeoff or landing.
Plain English
Anything on the runway that isn't dry pavement. Water, snow, ice, slush, and similar coverings make the surface slippery, which means longer stopping distances and harder steering on the ground.
Context Anchor
Encountered when checking runway condition before takeoff or landing, especially when deciding whether a rejected takeoff can be stopped safely.
Derivation
Contaminant comes from the Latin contaminare, meaning to make impure or pollute. In aviation it keeps that flavor: anything that 'pollutes' the clean, dry runway surface the airplane was designed to roll on.
Why Pilots Care
Unaccounted runway contaminants can increase required stopping distance and raise the risk of a runway overrun during a rejected takeoff.
Intuition Check
Do not assume runway contaminants only means trash or spilled material. In this context, normal weather effects like water, snow, slush, ice, and frost can also be contaminants.
Example Sentence 1
After overnight rain, the crew checked the runway condition report for contaminants before calculating takeoff distance.
Example Sentence 2
Awareness of runway contaminants helped the crew decide on a safe rejected takeoff procedure.