Visibility and cloudbase

Good visibility is vital for both pilots and air traffic controllers.

A good all-round view enables controllers to use visual observation to maintain aircraft separation. If that view is limited – by low cloud, say – separation has to be increased. Two factors are important in this respect: visibility (how far you can see) and ceiling (the height of the cloud base: the underside of cloud cover). The lower either of these is, the stricter the rules air traffic controllers and pilots must follow.

 

At all Dutch airports and airfields, the following criteria apply:

 

  • If visibility is greater than five kilometres and the ceiling higher than 1000 feet, no special precautions are required.

  • If visibility is between 1500 metres and five kilometres and/or the ceiling is between 300 and 1000 feet, special precautions are implemented. Visual approaches are not permitted and specific procedures apply to dependent (parallel) runways.

  • If visibility is less than 1500 metres and the ceiling lower than 300 feet, so-called “low visibility procedures” (LVP) take effect. Neither the pilot nor the air traffic controller is able to observe aircraft movements effectively. Under LVP, a number of additional safety precautions are applied: runways are protected with stop bar lights at their entrances and exits; aircraft separation is increased; runway usage and capacity are adjusted; work in the manoeuvring area is restricted or stopped altogether; and taxiing aircraft are actively supervised.

 

There are four categories of LVP, known as phases A-D, with D applying in the poorest conditions.

 

 

Meteorological observer in Radar Centre