Runway alternation

Update: 2013 Alternation Timetable

The map below 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 result of this switch over is to give some much valued relief for the half day period that they are not overhead.

BAA has published its alternation programme for year 2013(pdf, 128KB). 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. At present there is no alternation for the other 30%, when the aircraft take off towards London. However, this will change in a couple of years, when Heathrow has built some new taxi ways – following the cancellation of the ‘Cranford Agreement’.

The BAA programme 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 programme can again be changed if, for example, a strong wind comes from the ‘wrong’ direction.

The Government has now approved a ‘freedom trial’ to take place at Heathrow, starting on 1 November 2011.In pursuit of various benefits, the trial will have the unfortunate effect of disrupting the anticipated respite. Instead of enjoying long periods of noise relief, it is expected that there will be an increasing number of periods when aircraft will be flying on the wrong flight path. The Council understands the community concern about this. Although the published alternation programme itself will not be affected, it is the anticipated additional flights on the ‘wrong flight path’ that are causing the concern.

The Council welcomes the Government’s recent 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.