What determines the length of a airport runway?

Airport’s capacity is determined by several key factors, which includes size and the number of runways. Length of the runway is determined by aircraft type, ground surface type, longitudinal slope, altitude and the climate. It is also determined by the type of aircraft that will operate at the airport most frequently. Since there are different types of aircraft operating in different situations, there is a specification for every aircraft requiring a specific runway length.

For ideal design conditions, there will be a 0.0 % longitudinal slope of the runway, but geomorphological constraints can make the construction of the runway having a significant slope. The direction of the winds and keeping the above factors, whether the slope is positive or negative, will affect the length of the runway.

The friction coefficient between the runway and aircraft’s wheels directly affects take-offs and landings, and so determines the runway length. Runways are made of asphalt, cement, grass, earth, or compact snow. Altitude also affects the runway length. Runway length at altitude is higher than the sea level. As altitude increases, air density decreases, this decreases the thrust produced by the aircraft engine. Also, low air density results in less lift from the aircraft wings.

For climatic conditions, temperature is one of the important factors, which defines the length of the runway. Temperature affects the air density and higher temperature results in a lower air density.