Flight Path Maps
West Winds
When the wind is from the west which, according to BAA, is about 70% of the time, the two runways - north and south, are used. The way in which they are used varies throughout the day.
Between 6am and 7am both runways are in use for landings and take-offs. For the rest of the day one runway is used for landings and the other for take-offs. The roles of the runways are reversed at 3pm. This is called runway alternation. Each week the roles of the runways are changed relative to the week before so that if one week landings are on the south runway in the morning then the following week they will be on the on the north runway in the morning. The following animated maps illustrate this.
No attempt is made to represent the complex movements to and from the holding stacks over Bovingdon, Ockham, Lambourne and Biggin. Final approaches are joined around or probably before the Putney area. Take-off paths reflect the so-called "noise preferential routes" but it should be understood that the actual paths of aircraft can extend for several miles either side of those depicted.
West Wind 6-7
West Wind Morning
West Wind Afternoon
Between the last departure, theoretically no later than 11.30pm, and 6am an average (over the year) of 16 movements are permitted. These movements should be landings and take place on the same runway that was used in the morning.
East Winds
When the wind is from the east there is currently no runway alternation. Under the Cranford Agreement no take-offs are permitted from the north runway. This situation is illustrated as follows:
As before, the paths of the aircraft taking off reflect the "noise preferential routes". As part of their third runway plans the government wants to abandon the Cranford Agreement and allow runway alternation when the wind is from the east as well as from the west.
Third Runway
The government has announced that runway alternation will remain in place for the north and south runways when the wind is from the west. However alternation with the third runway is not possible and it will host both landings and take-offs all day. This is illustrated below. The third runway is marked in red. The south runway is in use for landings and the north for take-offs. In the alternative half of the day this arrangement would be reversed.
When the wind is from the east, runway alternation will be introduced for the north and south runways. Alternation will not be possible with runway three. This is illustrated below with the north runway used for landings and the south for take-offs. These two will change role for the other half of the day.
