Performance: declared distances, V1 and climb gradients
Declared distances
TORA (takeoff run), TODA (takeoff distance, may include clearway), ASDA (accelerate-stop distance, may include stopway), LDA (landing distance). Balanced field length exists when the one-engine-inoperative distance to continue equals the distance to stop - that is where V1 sits for a given mass. V1 is also limited by brake energy, tyre speed and minimum control speeds (Vmcg, Vmca).
Climb
Know the segments: the second segment (gear up, V2, takeoff flap) requires a minimum gross gradient of 2.4% for twins, 2.7% for three engines and 3.0% for four; the net gradient is gross minus 0.8%. Obstacle clearance in the takeoff flight path uses the net gradient.
Factors
Density altitude (pressure altitude corrected for temperature), runway slope, wind, surface condition, and bleed/anti-ice configuration all change the numbers. A wet or contaminated runway increases the accelerate-stop distance far more than the takeoff distance, which drives V1 reduction. Reverse thrust is never credit for the certified stopping distance.
Worked example
Ground run scales approximately as the square of the ground-speed ratio: run ∝ (1 − Vwind/Vlift-off)². With VLOF 140 kt and a 14 kt headwind, (1 − 0.1)² = 0.81 - about 19% shorter ground run. A 14 kt tailwind gives (1.1)² = 1.21, a 21% increase. Tailwind takeoffs are the expensive mistake.
Traps
Using actual landing mass instead of maximum certified landing mass for approach speeds; applying a headwind component to the climb gradient rather than to the flight path; forgetting a clearway may not be used in the accelerate-stop case.