The direction planes fly at Heathrow depends on the direction of the wind. Planes must take off and land into the wind for safety reasons.
Around Heathrow the wind usually blows from the west. Because aircraft must land into the wind, the majority of aircraft therefore arrive from the east (over London) and take off towards the west (over Berkshire/Surrey). This is known as westerly operations. Westerly operations occur for about 70% of the year.
When the wind blows from the east, the reverse happens. Aircraft arrive from the west (over Berkshire) and depart towards London. This is called easterly operations and we are ‘on easterlies’ for about 30% of the year.
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. It means that during periods of light easterly winds (up to 5 knots), planes will continue to land in a westerly direction making their final approach over London. At Heathrow, aircraft land over London for about 70% of the time.
The westerly preference was introduced in the 1960s to reduce the numbers of aircraft taking off in an easterly direction over London, i.e. over the most heavily populated side of the airport. This was when departures were considered to be more disruptive than arrivals to local communities.
The end of westerly preference?
Modern technology means planes have got quieter and climb more quickly nowadays 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 on making the best use of existing capacity in the short and medium terms, we proposed the ending of the westerly preference.
The Airports Commission supported this in its Interim Report (December 2013) and said that the Government should review the need for a westerly preference with a view to introducing a ‘no preference’ policy. We estimate that removing the westerly preference would reduce the number of arrivals over west London by around 5%.