Definition
The retarding force generated between the aircraft's tires and the runway surface when the brakes are applied during the landing roll. Its magnitude depends on the weight pressing the tires onto the runway and the coefficient of friction between the tires and the surface, which varies with runway condition (dry, wet, icy, contaminated).
Plain English
The slowing force you get from the brakes pushing the tires against the runway. How strong this force is depends on how much weight is on the wheels and how grippy the runway surface is.
Context Anchor
Seen in landing performance discussions, especially when explaining why runway surface condition, braking technique, and touchdown speed affect landing distance.
Derivation
“Braking” comes from “brake,” a device used to slow or stop motion. “Friction” comes from a Latin word meaning “to rub.” That helps here because the stopping force comes from the tires gripping and rubbing against the runway surface.
Why Pilots Care
It determines how much runway is needed to stop safely and changes with runway surface condition, tire condition, and aircraft weight.
Analogy
Like the force that slows your car when the brake pads press against the rotors and the tires grip the road.
Grounding Statement
After touchdown, the airplane can only slow through the forces actually acting on it, and braking friction force is the tire-and-runway force that helps stop it.
Intuition Check
Do not think of braking friction force as simply how hard the pilot presses the brake pedals. It is the actual stopping force available at the tires, and that force can be limited by runway grip.
Example Sentence 1
On the icy runway, braking friction force was so reduced that the landing roll nearly doubled compared to the dry-runway figure in the POH.
Example Sentence 2
Standing water on the runway lowered the braking friction force and increased the required landing distance.