Airport Operations & wind

[KelvinD]

Planning to go to Gatwick for a spot of rubbernecking, I noticed that the wind at both Heathrow and Gatwick tomorrow morning are forecast to be from the South, gradually veering toward the West later in the day. At Gatwick, the earlier winds (before dawn) will be SSE. 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?

[NudgingSteel]

Can't comment on those specific airports, but there are loads of considerations for runway-in-use selection! If the surface wind is straight across, the upper wind (i.e. on the approach) might be different - on occasions, a bit of a headwind on approach with a slight tailwind at touchdown might enable a more stabilised approach, than the other way round. Then there are things like approach aids (ILS availability etc), lighting, rapid exit taxiways, which might favour one end over the other. You are absolutely right that the forecast is also a consideration if it's 50/50 at the time.

Most airports will have a "preferred runway-in-use" which might be for local noise restrictions, airport layout or airspace considerations (how complicated the interaction between deps and arrs is, or even between adjacent airports eg LCY and LHR). That's often the overriding decider, even to the point that the preferred runway would be used even with a slight tailwind.

[DaveReidUK]

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.

[KelvinD]

Thanks Dave.
Speaking of Heathrow changes, did you see the recent news article about the residents of Henley moaning that far too many flights seem to be turning over their homes lately?
Out of curiosity, I replayed a couple of random early morning 09L arrivals and found some went beyond Henley to make the turn, while others turned well short. No wonder Heathrow seemed rather surprised at the reports!

[HEATHROW DIRECTOR]

Someone claimed that CPT departures made 180 degree turns over Henley! How they can publish such nonsesnse is beyond me.

[DaveReidUK]

Speaking of Heathrow changes, did you see the recent news article about the residents of Henley moaning that far too many flights seem to be turning over their homes lately?

Someone claimed that CPT departures made 180 degree turns over Henley! How they can publish such nonsense is beyond me.

I suspect both of the above relate to this BBC article

Henley-on-Thames residents challenge Heathrow aircraft noise - BBC News (http://www.bbc.co.uk/news/uk-england-oxfordshire-35380415)

in which the Henley MP says that "residents were not consulted over a trial that changed an aircraft route to go over Henley" and links that to the operational changes that NATS made last year to the "Compton Gate", used on the easterly CPT SID.