The slope of a runway, or gradient, is the difference in elevation from the beginning to the ending of the runway. Pilots use the slope, along with headwinds and tailwinds, to determine the speed needed for a successful takeoff and for a safe landing. Knowing the slope of a runway allows for an experienced pilot to maximize the effective length of the runway, and to successfully maneuver his craft on an incline or decline.
Subtract the elevation of the lower end of the runway from the higher end. For example, if the elevation of the higher end of the runway is 4,400 feet, and the lower end of the runway is 4,370 feet, then subtracting 4,000 by 4,3700 results in 30 feet.
Divide the difference of the elevations by the length of the runway. For the example, the length of the runway is 3,000 feet. Dividing 30 by 3,000 results in 0.01.
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Multiply that number by 100 to obtain the slope of the runway. For the example, the slope is 3, or a gradient of 3%.