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Directional preference

The direction planes arrive and depart from Heathrow depends on the direction of the wind. For safety and performance reasons aircraft typically take off and land into the wind. This is because an aircraft’s wing relies on the speed of the air moving over it (airspeed) to lift it off the ground.

During the day, a ‘westerly preference’ is operated at Heathrow which means that even during periods of light easterly winds (up to 5 knots – about 6 miles per hour) aircraft will continue to land in a westerly direction, making their final approach over London. This preference is in accordance with Government policy.

We are thinking of moving to a ‘managed’ preference which would involve changing the direction of arriving and departing aircraft based on a set of criteria or rules designed to limit overall noise effects on communities and to help deliver periods of relief for them.

Questions – Directional preference

While looking through the information below please keep in mind that we are asking for your feedback on the following question, with five parts:

  • Should we continue to prefer westerly operations during the day and easterly operations at night to reduce the total number of people affected by noise?
  • Any reasons for your answer
  • Should we sometimes intervene to change direction of operations to provide relief from prolonged periods of operating in one direction – even if that means slightly increasing the number of people affected by noise?
  • Any reasons for your answer
  • Any other comments or suggestions you have on directional preference.

What is directional preference?

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 and there is a choice. At Heathrow, winds are light on average 20% of the time.

How does "directional preference" work at Heathrow today and what affects does it have?

During the day, a ‘westerly preference’ is operated at Heathrow. This is Government policy and means that even during periods of light easterly winds aircraft will continue to land in a westerly direction, making their final approach over London.

This was introduced in the 1960s to reduce the number of aircraft taking off in an easterly direction over London, the most heavily populated side of the airport. This was when departures were considered to be more disruptive to local communities than arrivals.

In the UK, the wind is mostly from the south west. That means that with a westerly preference in place the majority of aircraft (approximately 70% a year) arrive from the east (over London) and take off towards the west (over Berkshire/Surrey). This is known as ‘westerly operations’

When the wind blows from the east (and is over five knots), the direction of operation is switched and aircraft land from the west over Berkshire and take off towards the east. This is known as ‘easterly operations’ and occurs approximately 30% of the time.

IMAGE: Diagram explaining Westerly operations at Heathrow. When the wind blows from the west, planes land over London and take off towards the west. Westerly operations account for 70% of the year on average.
Westerly operations
IMAGE: Diagram explaining Easterly operations at Heathrow. When the wind blows from the east, planes land over Windsor and take off towards London. Easterly operations account for 30% of the year on average.
Easterly operations

Is westerly preference also in place during the night?

Following consultation in 2001, the Government decided that the westerly preference should be removed at night and particularly during the early morning period when there are more arrivals than departures.

This means that instead of westerly preference at night, we rotate between westerly and easterly operations to provide a fairer distribution of aircraft noise to the east and west of the airport. We can only do this when the wind direction allows us to or is below 5 knots.

What considerations are involved in moving to a managed preference for operations at Heathrow?

Moving to a “managed preference” would involve changing the direction of arriving and departing aircraft based on a set of criteria or rules designed to limit overall noise effects on communities and to help deliver periods of relief.

Factors to consider on this topic include the following:

  • If we wanted to minimise the number of people adversely affected by aircraft noise we could operate in a westerly direction during the day and in an easterly direction at night;
  • We also know from stakeholder engagement and feedback that long periods of operation in any one direction, and the potential combined impacts of our operations with other airports (such as London City), are important issues that people experience with the current system of westerly preference;
  • A managed preference could be used to break up periods of operating in one direction for example after five or seven days (if the wind is low enough to allow a change).

Our work so far shows that if we managed the preference to minimise the total number of people affected by noise, it would mean that if there is a choice to do so, we should use westerly operations during the day and easterly operations at night.

Unlike during the day, easterly operations at night would minimise the total people affected by noise. This is because the majority of flights at night are arriving aircraft (which are quieter than departing aircraft) and would arrive from the west which is less densely populated compared to the east of the airport (London).

What are the alternatives to implementing a managed preference for Heathrow?

There are 3 alternatives to implementing a managed preference for the direction of operations:

Westerly preference

As previously described, this is the existing directional preference used at Heathrow and has been in place for over 50 years. Factors to consider regarding Westerly preference:

  • It reduces overall effects of noise on communities and reduces the total population exposed to noise (compared to easterly preference). 
  • It is perceived to be an unfair balance of noise as communities to the west of the airport have longer periods of departing aircraft (which are slightly noisier than arriving aircraft) than communities to the east. Also, if we were to remain on westerly preference at night a larger population could be affected by noise due to the greater number of arrivals over central London at this time.

Easterly preference

This would involve switching the currently westerly preference to an easterly preference. It would mean that we would stay on easterly operations even if the wind were coming from the west (and is below 5 knots – about 6 miles per hour) for as long as possible. As the wind comes predominantly from the south west it would result in a roughly 50/50 split in easterly and westerly operations over the long term at Heathrow. 

Factors to consider on this topic include, that:

  • Easterly preference would deliver a more balanced split between easterly and westerly operations – sharing noise across communities to the east and west of the airport for arrivals and departures. 
  • An easterly preference at night would reduce the overall population affected by noise as more aircraft would be arriving to the west of the airport over less densely populated areas. 
  • But easterly preference could result in more people being affected by noise overall because more departing aircraft (which are slightly noisier than arriving aircraft) would be flying over densely populated central London. 

No preference

A no preference policy would mean that Heathrow would switch operations whenever the wind changes.

Factors to consider regarding no preference include the following:

  • A no preference policy would result in a much less predictable operation and could mean that we have to switch the direction of arriving and departing aircraft a number of times over the course of a day. 
  • This option would be difficult for Heathrow to operate as each change of operations from westerly to easterly (or vice versa) takes time and can cause delays. 
  • It is also the least predictable option for communities whose respite could be interrupted due to the much more frequent changes.

What questions are you asking for feedback on in this section of the consultation?

In this section we are asking for feedback on the following question, with five parts:

  • Should we continue to prefer westerly operations during the day and easterly operations at night to reduce the total number of people affected by noise?
  • Any reasons for your answer
  • Should we sometimes intervene to change direction of operations to provide relief from prolonged periods of operating in one direction – even if that means slightly increasing the number of people affected by noise?
  • Any reasons for your answer
  • Any other comments or suggestions you have on directional preference.