The direction planes fly at 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 in order to create lift, an aircraft’s wing relies on the speed of the air moving over it (airspeed).
In the UK, the wind is mostly from the south west. That means 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.
The percentage of westerlies and easterly operations varies from week to week and month to month. It is also affected by our ‘westerly preference’. We provide live updates on the direction Heathrow is operating via our website and twitter feed (follow us @HeathrowNoise).
The direction of operation is determined by NATS air traffic controllers who monitor wind speed and direction on the airfield and at different levels up to 3,000ft. The position is kept under constant review. The weather forecast made by the Met Office is not always a reliable indicator of what is happening at Heathrow since the Met Office forecast for the public relates to ground level.
Due to the direction of operation determined by the wind, the operation can change direction more than once in a day. We therefore are unable to control or predict which direction the airport will be operating in.
During the day, a ‘westerly preference’ is operated at Heathrow. Westerly preference is Government policy and means that even during periods of light easterly winds (up to 5 knots) aircraft will continue to land in a westerly direction, making their final approach over London.
Westerly preference 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 2001, following consultation, the DfT decided that the westerly preference should be removed at night, to provide a more equitable distribution of aircraft noise.
The end of westerly preference?
Modern technology means planes have got quieter and climb more quickly, and therefore questions have been raised as to whether the westerly preference is still relevant today. In Heathrow’s submission to the Airports Commission in May 2013 we proposed the ending of the westerly preference and the Airports Commission supported a ‘no preference’ policy in its Interim Report.
Because the westerly preference is current Government policy, the ending of it would have to be subject to Government approval and public consultation.
In the interests of fairness, our view is that the ending of the westerly preference should not be introduced until there is full runway alternation on easterly operations. We estimate that removing the westerly preference would increase the percentage of easterly operations (aircraft arriving from the west and departing to the east) by around 5 per cent.
For more information about Heathrow's operations, you can download the Heathrow Operations Handbook 2018.