Definition
A runway is considered contaminated whenever standing water, snow, slush, ice, or similar matter is present on more than 25 percent of the runway surface area within the reported length and width being used, in depths that affect aircraft braking performance and directional control.
Plain English
A runway with enough water, snow, slush, or ice on it to change how the aircraft stops and steers during takeoff or landing.
Context Anchor
You will see this term in runway condition reports, weather-related airport information, and takeoff or landing performance decisions.
Derivation
Contaminated comes from the Latin contaminare, meaning to make impure or to spoil by mixing in something foreign. In aviation, the runway surface is being spoiled for normal use by something that should not be there.
Why Pilots Care
Contaminants increase required landing and takeoff distances, reduce braking effectiveness, and can lead to hydroplaning or loss of directional control.
Grounding Statement
A dry runway gives the tires their best grip; a runway covered with water, snow, ice, or slush may not.
Intuition Check
Do not read contaminated as meaning dirty or unusable. In this FAA sense, it means the runway surface is covered enough by water, snow, ice, or similar material to affect airplane performance.
Example Sentence 1
The crew calculated new landing distances after the tower reported the runway was contaminated with half an inch of wet snow.
Example Sentence 2
Takeoff performance data must be adjusted when the runway is reported as contaminated to ensure adequate accelerate-stop distance remains available.