Periods of relief from aircraft noise
We know that aircraft noise can be disruptive to some people around Heathrow. So we use a mechanism known as runway alternation to share the burden and to give everyone periods of relief from aircraft noise when we are westerly operations.
At its heart, runway alternation is straightforward: for part of the day we use one runway for landings and the other for take-offs. Halfway through the day we switch over as shown in the graphic below . If you were living or working under the arrivals flight path during the morning, you're unlikely to be under it during the afternoon. And vice versa.
To help you plan ahead, we publish an annual schedule of runway use. It tells you which runway we're using any day or night of the year. The schedule covers landings only because that's where runway alternation makes the biggest difference.
Runway alternation schedule 2016 (183KB PDF)
How does runway alternation work
In practice runway alternation is more complicated than the simple explanation above. At any given time, our choices of runway and flight direction also have to take account of the six factors listed below.
- Daytime patterns of runway alternation are different to night-time patterns: at night there are only a handful of landings and very few take-offs [see full explanation below]
- Aircraft land and take off into the wind, so the wind direction has a big effect on flight patterns
- Government policy currently favours aircraft taking off towards the west. Even when the wind blows from the east, aircraft could still fly in from east and take off towards the west. This is because we have a westerly preference
- A historical restriction means that aircraft cannot take off towards the east from the northern runway. This is because of the Cranford Agreement
- The hour between 06:00 and 07:00 is the busiest time of the day for arrivals so we are able to use both runways for landings
- Occasionally we have to suspend runway alternation for airfield maintenance, in response to bad weather or when air-traffic control want to avoid a build-up of arriving aircraft.
Daytime runway alternation
Daytime runway alternation follows a daily cycle and a fortnightly cycle. Alternation starts at 06:00 and continues till the last aircraft departs at the end of the day.
- In the morning we use one runway for take-offs and the other for landings. At 15:00 – roughly halfway through Heathrow's working day – we swap over
- We continue this morning and evening pattern of runway use for the rest of the week
- The following week we switch completely. What we did in the evening during the previous week, we now do in the morning. And vice versa
Runway alternation gives everyone an equal share of respite from aircraft noise. The diagram below shows how it works when the wind blows from the west. Runway alternation during the day is not currently possible when the wind blows from the east.
Night-time runway alternation
Since there are very few aircraft take-off or landing at night there’s more scope for runway alternation whether we are on easterly or westerly operations. We can switch landings between the northern and southern runways and, if the weather allows it, we can bring in aircraft from the east or the west.
Those four options allow us to operate night-time runway alternation on a four-weekly cycle.
- Week 1: Aircraft fly in from the west to land on the northern runway.
- Week 2: Aircraft fly in from the east to land on the northern runway.
- Week 3: Aircraft fly in from the west to land on the southern runway
- Week 4: Aircraft fly in from the east to land on the southern runway.
Since the wind direction and strength can have an impact on this pattern, we always specify a primary and a secondary (alternative) runway in our schedule.