Definition
The degree to which an airplane's wheel brakes can actually slow the airplane during the landing roll, determined by the friction available between the tires and the runway surface. Braking effectivity is reduced by water, snow, ice, slush, rubber deposits, or any condition that lowers tire-to-runway friction, and it depends on sufficient weight being on the wheels for the brakes to bite.
Plain English
How well the brakes will actually stop the airplane on the runway you are using. Good runway and dry tires mean the brakes work well. A wet, icy, or contaminated runway means the brakes work less well, no matter how hard you press the pedals.
Context Anchor
You will see this term in landing discussions, especially when runway surfaces are wet, icy, contaminated, or otherwise not providing normal tire grip.
Derivation
From 'effective' (Latin effectivus, 'producing a result') with the suffix '-ivity' meaning 'the quality or degree of.' Braking effectivity literally means 'how much result the braking produces' — useful because it reminds you this is about real-world stopping performance, not how hard you press the pedals.
Why Pilots Care
Directly affects the calculated landing distance and the decision to land or go around on short or slippery runways.
Intuition Check
Do not assume braking effectivity means how hard the pilot presses the brakes. It means how well the airplane actually slows down, which also depends on tire grip and runway condition.
Example Sentence 1
The tower reported braking effectivity as poor on the first half of the runway due to standing water, so the captain elected to divert to a longer, drier runway.
Example Sentence 2
After the preflight, the instructor reminded the student that heavy braking early in the rollout improves effectivity before aerodynamic braking fades.