Definition
The grip available between the airplane's tires and the runway surface, which determines how effectively the airplane can accelerate, steer, and brake during ground operations. Runway friction is reduced by water, snow, slush, ice, rubber deposits, or loose debris, and varies with surface type, temperature, and tire condition.
Plain English
How much grip the tires have on the runway. More grip means better stopping and steering. Less grip — from rain, ice, or snow — means the airplane needs more distance to stop and is harder to control on the ground.
Context Anchor
Encountered during takeoff and landing performance planning, runway condition reports, and rejected takeoff decisions.
Derivation
Friction comes from the Latin word fricare, meaning “to rub.” That fits the aviation meaning because runway friction is created by the tires pressing and rubbing against the runway surface instead of sliding freely over it.
Why Pilots Care
Low runway friction lengthens the stopping distance, which can turn a safe rejected takeoff into a runway overrun if not accounted for.
Analogy
It is like the difference between stopping a bicycle on dry pavement and on ice. The brakes may work the same way, but the surface decides how much grip is available.
Grounding Statement
Picture the tires trying to bite into the runway as the pilot brakes; if the surface is wet or icy, that bite is weaker.
Intuition Check
Runway friction is not just about how rough the runway looks. It means the actual tire grip available for braking and steering on that surface at that time.
Example Sentence 1
After the rain shower, the captain expected reduced runway friction and added a margin to the planned stopping distance.
Example Sentence 2
Standing water reduced runway friction and doubled the distance needed to bring the airplane to a stop.