Weather and air traffic
Brief guide to fog and air traffic at Bromma Stockholm
What is fog?
Fog is when meteorological visibility is less than 1,000 metres. Fog is a frequently occurring phenomenon during the autumn.
What does LVP mean and why is it associated with fog?
When we have vertical visibility of less than 200 feet and the runway visual range (RVR) is less than 550 metres, we implement what are known as low visibility procedures (LVP).
LVP means that we have a maximum of one aircraft movement at a time in the manoeuvring area (taxiway and take-off/landing runway). This is intended to eliminate the risk of an unintended runway incursion in conjunction with take-off and landing.
When LVP is in effect, capacity is significantly restricted so that a landing aircraft must arrive at the apron before the next landing can take place or before the next aircraft taking off can begin taxiing. Depending on whether traffic consists of only aircraft taking off or landing or a mixture of the two at the same time, we must have different distances between the aircraft.
Different airlines have different minimum requirements to begin an approach. At Bromma Stockholm, it is usually 550 metres to Runway 12 and 750 metres (CAT I ILS) to Runway 30. The reason for this difference between the runways is the approach lighting. Airlines are the ones that set limits, but they can never be lower than those approved by the Swedish Transport Agency.
Why is it sometimes possible to take off but not land?
Take-offs generally have a lower runway visual range (RVR) required than landings. That is, take-offs are usually possible even if it is not possible to land. Take-offs are possible with RVR as low as 250 metres at Bromma Stockholm (regulated in LFS 2007:50 as well as in EU-OPS).
How does “marginal weather” work?
If there is “marginal weather,” that is, weather conditions in which the visibility or distance from clouds fluctuates between within and just outside the range of what it should be for take-off or landing, restrictions are put in place to prevent too many aircraft from flying around Stockholm in a holding pattern while waiting for visibility to improve so that they can begin their approach. As a result, flights may be given a calculated take-off time (CTOT), known in common parlance as a ”slot,” which means they have to wait on the ground at the airport they are taking off from instead of in the air.