Runway Alternation*

We know that communities around Heathrow value relief from aircraft that can be provided by runway alternation.

*This page contains one (1) question located within the “Have your say” section at the bottom of the page.

During the day, when planes are landing and taking off to the west (westerly operations), we alternate the use of our two runways to provide local communities with respite.

Heathrow’s current alternation pattern

The current alternation pattern means that for part of the day we use one runway for landings and the other for take-offs then, halfway through our day at 3pm, we switch over.

At the end of each week we switch completely. What we did in the evening during the previous week, we now do in the morning and vice versa.

This is so that communities get respite from planes in the morning one week and in the evening the next.

When planes take off and land towards the east (easterly operations) we do not alternate the runways because the taxiways are not currently in place for us to do so during daytime operations because of the legacy of the Cranford Agreement.

Runway alternation - Westerly operations - Week 1
When on westerly operations we operate a runway alternation programme that runs in a two week cycle. This gives residents living under both runway flight paths predictable relief from aircraft noise for half the day.
Runway alternation - Westerly operations - Week 2

What is the Cranford Agreement?

The Cranford Agreement was an agreement between the Government and the residents of Cranford which restricted the number of take offs from our northern runway in an easterly direction over the village.

The agreement is no longer in place. Further details can be found at:

At the Airspace and Future Operations Consultation in January 2019 we presented a potential runway alternation pattern to be used for a three runway Heathrow and asked whether people would prefer to have longer periods of respite less frequently (all day on some days but no relief on other days) or a shorter period of respite (e.g. for 4-5 hours) every day.

Feedback from the consultation told us that people value respite early in the morning, later in the evening and in the night time. We have taken this feedback on board and are proposing a runway alternation pattern that maximises respite at these times and provides for runway alternation every day during the day.

Proposed runway alternation pattern for an expanded Heathrow

Currently, we mainly use one runway for departures and one runway for arrivals. With three runways we will be changing this so that one runway is used for arrivals, one runway is used for departures and the remaining runway is ‘mixed mode’ which means it will be used for both departures and arrivals.

Having three runways allows us to rotate their use so that they may be used in turn for landings, departures or in “mixed mode”.

The diagram below illustrates the idea and shows that alternating the use of the runways allows communities at the end of the runways to have a break from overflying, whether aircraft are landing from the east or from the west.

Arrivals runway
Arriving aircraft can land as soon as the aircraft in front has exited the runway
Departures runway
Departing aircraft can usually take off as soon as the aircraft in front has left the runway
Mixed mode runway
Arriving and departing aircraft use the mixed mode runway. But the landings and departures are not quite as frequent as they are with the arrivals or departures runways. For example, an arriving aircraft has to wait both for any arriving aircraft to exit the runway or for any departing aircraft to complete its take off before that arriving aircraft can land. Sometimes the mixed mode runway will have more arrivals than departures and vice versa. This is common practice around the world.

What is a runway mode?

A runway mode means whether a runway is used for landings or departures, or both. If a runway is used for either landings or departures, we call this “segregated mode”. If it is used for both landings and departures at the same time but usually less intensively – we call this “mixed mode”.

What is mode allocation?

Mode allocation is how we describe how runway modes are used together across all the runways at one time. For example, the new third runway might be allocated to a “mixed mode”, the centre runway on a “segregated arrivals mode” and the southern runway on a “segregated departures mode”. We have developed four different arrangements for mode allocation between the three runways.

The four different mode allocations

Runway mode allocation 1 (Westerly operations)
Runway mode allocation 2 (Westerly operations)
Runway mode allocation 3 (Westerly operations)
Runway mode allocation 4 (Westerly operations)

There are technical restraints which determine the order we can move around the mode allocations. We are proposing that we will move through them in the following order:

Our proposed daily runway alternation pattern will repeat this sequence every four days. So, on Day 5 we would start again as Day 1. Within each day, the change from the first mode allocation to the second mode allocation can happen either at 14:00 or 15:00 (we are seeking your views as to when exactly it should change) and again at midnight. This change at midnight is in preparation for the following operational day and occurs when there are no scheduled movements taking place.

We also have the opportunity to ensure that when the wind changes direction and we have to change the direction in which we operate the runways (so from westerly to easterly and vice versa), that communities continue to receive the respite that they were expecting, something that is not possible today due to the Cranford Agreement. We are calling this Reflective Alternation.

Have your say

In response to our previous consultation, we have developed a combined runway alternation and night flights scheme which prioritises respite for communities closest to the airport in the evening, night and early morning periods. As part of our plans for runway alternation, we are proposing four runway operating patterns. We would rotate between these patterns at either 2pm or 3pm and again at midnight each day. The sequence of these patterns will be repeated every four days.

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