Highways in the air
We now know how an aircraft flies, but how does it find its way to the airport it is heading for? Before takeoff, each aircraft is allocated a prescribed route. Think of these routes as invisible highways through the air. The air traffic controllers see to it that the aircraft doesn’t “leave the road”. The maintain contact with the aircraft from the control tower at the airport.

They give permission for take off and landing, they instruct the pilot which runway to use and they indicate the height and direction an aircraft needs to reach its destination. Radar screens allow an air traffic controller to plot the exact position of each aircraft that is in the area they control.

You might ask how a pilot manages to find the route that he must follow. After all, there are no signposts in the sky. For air traffic, the function of signposts is taken over by satellites and radio beacons. Radio beacons are a kind of transmitter on the ground that transmits signals that can be received by aircraft. These signals inform the pilot of his current position, and the direction he must fly to reach the next radio beacon.

Satellites have a similar function, but operate from their orbit above the earth. These navigation satellites orbit at a height of 37,000km (23,000 miles) so that from earth, they look as if they are standing still. Thanks to the radio beacons and navigation satellites, pilots always know exactly where they are, even if they are above the clouds or flying in the dark.

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