Control Towers and Runways

The nerve center of a larger airport is the control tower. Air traffic controllers use radar, computers, and radio to direct the movement of airplanes in and out of the airport and on runways. The design and layout of runways is regulated by the government and by the International Civil Aviation Organization, to which most nations belong.

Early airplanes were light enough to land on a grass airfield. Modern passen­ger and cargo planes are so heavy that they need hard runways, constructed of concrete or tarmacadam. Because most modern jet planes need a lot of space to take off and land, runways have become longer, and airports now take up a lot of ground.

A typical airport today has a single main runway, often over 13,000 feet (3,960 meters) long. The runway must be long and wide enough for the largest

WIND FACTORS

Aircraft usually land and take off into the wind. For this reason, older airports had three or four runways, arranged in the shape of a triangle or box, so aircraft could land and take off no matter which direction the wind was blowing. Modern air­planes are so powerful that they are less affected by wind, and a modern airport can often operate efficiently with just one main runway. It may need extra runways, however, to cope with the number of passengers and amount of air cargo.

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planes flying into the airport to take off and land safely. A runway has a clear space at each end in case a pilot requires extra distance when taking off or land­ing. Numbers on or beside the runway identify it by compass direction. For example, on a north-south runway, the numbers are 18 (short for 180°) at the north end, and 36 (short for 360°) at the south end. White lights mark the edges of the runway, and green lights are placed where the runway starts. There is an additional set of red and white approach lights, which pilots see as they prepare to touch down.