How is landing performance calculated and certified?

Landing performance determines runway length requirement. Calculation: Approach - At 50 ft threshold, Vref = 1.23*Vstall minimum; Flare - Transition from approach to touchdown; Ground roll - Deceleration with brakes, spoilers, and reverse thrust. Regulatory: Demonstrated landing distance multiplied by factor (1.67 for transports) for operational use. Factors affecting performance: Landing weight, altitude and temperature, runway condition (dry, wet, contaminated), and wind (credit limited to 50% headwind). Braking: Antiskid system prevents lockup, Autobrake settings, and Carbon vs. steel brakes. Deceleration devices: Spoilers (dump lift, add drag), Reverse thrust (credit varies), and Wheel brakes. Wet runway: FAR/CS 25.1592, landing on contaminated surfaces. Certification: Flight test demonstrated distances, Performance data validated. Airlines dispatch based on actual runway available vs. required landing distance including factors.