Originally Posted by
KelvinD
Given that neither airport has a N-S runway, how do the ATC determine which direction they will operate when the winds are southerly? Do they calculate that, as the wind will go West later, they might as well start off with westerlies?
Heathrow's runway alternation programme incorporates a westerly preference, effective from 0600LT onwards, so in a southerly wind 27s will be used.
Prior to 0600, easterly and westerly preference each operate 50% of the time to distribute early morning arrivals flighpaths more equitably between 09s and 27s, although ATC routinely avoid having to swap runways at 6 by ignoring easterly preference if winds will allow westerly operations (a practice Heathrow pledged earlier this month to end).
Gatwick doesn't operate any formalised directional preference, so in a southerly wind either 08 or 26 could be in use.