Landing performance
The landing chain
Landing performance starts at the 50 ft screen height and ends at a full stop. The landing distance available (LDA) must cover the landing distance required; the manual figure is the demonstrated distance multiplied by a factor of 1.67 for a dry runway (or 1.92 for a wet runway in older rules). The approach is flown at VREF, which is 1.3 times the stall speed in the landing configuration, and the aircraft crosses the threshold at VREF. Reverse thrust and automatic braking affect the stopping distance but are not always credited.
What lengthens the landing
Higher landing mass, higher pressure altitude, higher temperature, tailwind, downslope, wet or contaminated runway, and a higher flap setting all increase the landing distance. A trap is the wind: landing performance is quoted for still air, so a tailwind must be added, and a headwind cannot be assumed. Another trap is the difference between the dry and wet factors and whether reverse thrust is included. Contaminated runways need separate data, and a runway is contaminated when standing water, slush or snow exceeds a defined depth.
Worked example and rule of thumb
A manual gives a dry landing distance of 1,100 m at the actual mass and conditions. Applying the 1.67 factor gives 1,100 × 1.67 = 1,837 m required. If the LDA is 2,000 m, the landing is legal with 163 m margin. For a wet runway with a 1.92 factor, the required distance becomes 1,100 × 1.92 = 2,112 m, exceeding the LDA, so the landing mass must be reduced. Rule of thumb: a 10 kt tailwind adds about 20% to the landing distance.