Runway alternation is used to spread the impact of airport noise across local communities. Switching departures and landings from one runway to the other part way through the day helps ensure that the noise is shared across different communities each day.
The map shows that two arrivals paths are used by aircraft coming in to land at Heathrow. Normally only one path is used at a time. To a pilot approaching Heathrow from the London side (from the right), there is one runway to the right (27R) and one to the left (27L). The ‘27’ is short hand for the due west compass bearing they fly.
Runway alternation is employed every day at Heathrow. It has the effect of giving either morning or afternoon respite to the communities between London and Heathrow. The switch over occurs at 3pm, when, for example, aircraft coming in to land to the southern runway will be directed to switch over and come in instead on the northern runway. The purpose of this switchover is to give some relief to those living beneath the flight path, for the half day period that they are not overhead.
Heathrow publish a runway alternation schedule. It shows which runway is designated for use, when the wind is westerly – which is the prevailing wind for 70% of the year. Westerly arrivals are those aircraft flying towards Heathrow from the London direction.
The schedule shows that the night time alternation arrangement is more complex, as it involves the Sunday to Monday switch over, plus a night time rotation arrangement, to share the noise between the four approach routes to Heathrow. This schedule may also change if, for example, a strong wind comes from the ‘wrong’ direction.
We support the Government’s commitment to retain runway alternation at Heathrow and that there will be no increase in the number of flights, which will remain capped at current levels.
Updated: 20 November 2015