Flight Performance
Flight Performance tests whether you can predict what the aeroplane will actually do on a specific runway on a specific day at a specific mass - and whether you know which limit bites first.
The declared distances
TORA is the take-off run available; TODA adds the clearway; ASDA adds the stopway; LDA is the landing distance available. The graph take-off distance normally includes the air segment to 35 ft (50 ft for some types), so the ground roll alone is shorter. Clearway may not be counted for landing. Never plan beyond the declared distance.
What changes the numbers
Density altitude, mass, wind, slope, surface and configuration. Warm, high, humid air lowers density, so thrust and lift fall and both take-off distance and climb gradient suffer. Mass matters most: a 10% mass increase raises take-off distance by roughly 20%, because acceleration falls and the speed needed is higher. A headwind equal to 10% of lift-off speed cuts ground roll by about 19%; a tailwind of the same size lengthens it much more. An upslope lengthens the take-off run and flattens the climb gradient.
Climb and V speeds
Vx gives the greatest height gain per unit ground distance and is used for obstacle clearance; Vy gives the greatest rate of climb. With increasing altitude Vx rises and Vy falls until they meet at the absolute ceiling. V1 is the decision speed, VR the rotation speed, V2 the take-off safety speed at which control is maintained after an engine failure.
Worked example
Pressure altitude 5,000 ft, OAT 30°C. ISA temperature at 5,000 ft = 15 − (2 × 5) = 5°C, so the ISA deviation is +25°C. Using the 120 ft per °C rule, density altitude ≈ 5,000 + (25 × 120) = 8,000 ft. Enter the take-off graph at 8,000 ft pressure altitude, not 5,000 ft, and expect a markedly longer run and a shallower gradient.
Traps that cost marks
Entering the graph with pressure altitude when density altitude is required; treating a tailwind as a headwind; assuming distance rises linearly with mass; and applying wind or slope corrections at the wrong stage of the graph.