When winds are light (below 5 knots – about 6 miles per hour) aircraft can potentially take off or land in either direction. Rules are set by Government to determine what to do in these circumstances. These are called a “directional preference” and they say in which direction operations should be when the winds are light enough for there to be a choice.
Currently during the day, a ‘westerly preference’ is operated at Heathrow. This means that even during periods of light easterly winds aircraft will continue to land in a westerly direction, making their final approach to land over London. With this westerly preference in place the result is as shown in the diagram below.
As a long term average, the wind direction means that we have to have westerly operations for approximately 50% of the time, and easterly operations for approximately 30% of the time. The current westerly preference means that the remaining 20% of the time, where wind speeds are low enough to operate in either direction, we choose to operate in a westerly direction. Therefore, applying a “directional preference” in the future will only apply to this 20%.
Feedback from our previous consultation
At the Airspace and Future Operations Consultation in January 2019, we asked for feedback on how we manage the direction of arriving and departing planes at Heathrow.
Feedback from the consultation showed support for measures which help to deliver respite from aircraft noise. Responses also showed a preference for Heathrow to intervene if planes have been operating in the same direction for a long time.
Accordingly, we are proposing to operate an expanded Heathrow using a ‘managed preference’ not the ‘westerly preference’ we use today.
This would involve changing the direction of arriving and departing aircraft based on a set of criteria or rules (which are to be determined), designed to limit overall noise effects on communities and to help deliver periods of relief for them, when considered with our proposals for runway alternation.
Between now and Devlopment Consent Order (DCO) application submission we will explore the use of managed preference to reduce the effects of aircraft noise for our communities through engagement with our key stakeholders and communities. Our proposals will be presented in our DCO application.
A managed preference could be used to break up long periods of operating in one direction, if the wind is low enough to allow a change.
A managed preference would achieve a balance between minimising the total number of people adversely affected by aircraft noise, a fairer sharing of arriving and departing aircraft and the most efficient operation for the airport, due to reducing the need to switch operating direction multiple times during the day.
When put together with our proposals for a reflective runway alternation scheme, communities at the ends of the runways will receive much greater predictability over the amount of respite that will be provided.
For more information on our proposals for directional preference, and what effect these may have on communities, please read the Future Runway Operations document.