How do planes land in fog?
When it is foggy, runways send out invisible radio beams that guide planes down. Two needles on a dial show the pilot whether to go up or down, left or right.
An instrument landing system sends two radio beams from the runway. The plane’s instruments show whether it is above or below, left or right of the beams.
Two beams
The localiser beam runs along the centre line of the runway and tells the plane if it is left or right. The glideslope beam slopes down at about 3 degrees and says if the plane is too high or too low.
Reading the needles
Two needles cross in the middle of the instrument. If both are centred, the plane is exactly on the path. If a needle is off to one side or below the centre, the beam is that way, so the pilot steers towards it.
Down to the minimum
The pilot follows the beams down to a set height called the decision height. If the runway lights are not in sight by then, the pilot goes around.