Fog

When fog reduces visibility at the airport, it can be necessary to restrict aircraft landings. If visibility is poor, aircraft have to be kept farther apart from each other, i.e. longer times between take-offs and landings.

Copenhagen Airport uses the terms "horizontal visibility" and "vertical visibility" to mean how far ahead and how high up one can see. The runway visual range, or RVR, indicates how many metres one can see straight ahead, i.e. on a runway, whilst vertical visibility indicates how many feet one can see directly up, i.e. when looking straight up from the runway.

These two indicators determine whether visibility conditions are Category 1, Category 2 or Category 3. Category 1 is clear weather, whereas Categories 2 and 3 indicate different degrees of poor visibility.

Category 3 means that visibility at the airport is under 200 metres, and this classification often results in traffic restrictions. Category 3 visibility is a problem for traffic at Copenhagen Airport for a total of 48 to 72 hours a year.

The small candy-striped buildings at the end of the runways are called ILS (Instrument Landing System) huts. Because of the equipment in these buildings, aircraft can land at the airport in any kind of weather.
            
The ILS equipment sends one signal up into the air at an angle that indicates the angle the aircraft must follow in its approach and a second signal that indicates the direction of the runway. Both signals are picked up by an antenna in the plane at a distance of 16 km and transmitted to the autopilot. This function is very important, especially in foggy weather. The newest types of aircraft can land on autopilot alone.

Except for the fact that large planes, when they take off, can move air in such a way that causes the fog nearby to lift for a little bit, not much can be done about this phenomenon. Fog has an effect on traffic at Copenhagen Airport in the autumn and winter particularly.