The use of an airfield is controlled to a certain extent by the wind, and if the cross component of the wind on the runway exceeds a certain strength, it becomes hazardous for an aircraft to land or take off. The effect of a cross-wind component on aircraft in flight is to cause drift, whereby the path of the aircraft over the ground is inclined at an angle to the direction in which the aircraft is steered. A pilot about to land in a cross-wind must execute a certain manoeuvre to counteract the drift, otherwise on touching down the aircraft will tend to move sideways across the aerodrome, thus putting a strain on its undercarriage and perhaps tipping over on to one wing.