Heathrow Easterlies.

[PhineasC]

I could be wrong but this morning Heathrow and London City arrivals were on easterlies, around noon Heathrow switched to westerlies but London City is still on easterlies.

Anybody shed any light?

[DaveReidUK]

Heathrow operates a westerly preference (27s are used in light easterly winds).

LCY doesn't.

[Peter47]

It is not uncommon for Heathrow & Gatwick to be operating in different directions and I dare say that it happens at LHR & LCY. I'm not an ATCO so I can't comment on the conflicts that it could cause.

It could be that wind direction was different. If the wind direction changes one airport may swap runway direction earlier than another.

[WHBM]

Wind was light easterly all day. There was a very significant fire in Dagenham in the afternoon whose smoke plume blew to the west, north of LCY, who were on easterlies as long as I noticed them.

It's not unusual for LCY to be on easterlies and Heathrow on westerlies. As I understand it (to be corrected by those close to it) the inbounds to LCY approach downwind on the south and turn right base right overhead the London Eye at Waterloo, and back onto finals at 2,000 ft, while Heathrow inbounds are not beolw 3,000 ft until passing this point.

In passing, I was wondering today as I observed all this how LCY (and just about every other airport, of course) carries on operating easterly departures no problem when there is a significant fire in the vicinity with smoke obviously drifting across the departure route, but when there is a volcano 1,500 miles away, with absolutely no detectable trace, the whole air system of the country is shut down ......

[Groundloop]

Heathrow only switches to easterly operations when the tailwind component on westerlies exceeds 5 knots. This is for noise purposes.

Because of the short runway at City runway direction switches as soon as there is ANY tailwind component.

[betterfromabove]

This is strange....surely the noise footprint on westerlies at LHR covers more population than that on easterlies?

Or is it to do with fact that there is no runway rotation at 3pm?

Do strong crosswinds have an influence on choice as well? Presume the hangars and buildings on 27 finals must be troublesome in strong such conditions?

[DaveReidUK]

This might help:

"A 'westerly preference' has been operated at Heathrow since 1962 as a noise mitigation measure. The preference provides for 'westerly operations' (i.e. when landing aircraft approach Heathrow from the east over London and take off to the west over Berkshire) to continue when there is a light easterly following wind up to 5-knots, if the runways are dry and any cross-wind does not exceed 12-knots. Maintaining westerly operations in this way reduces the need for aircraft to take off in an easterly direction over Hounslow, Ealing, Twickenham etc., where the departure routes cannot be designed to avoid the most densely populated areas; in contrast to the position west of the airport where the departure routes pass between the main built-up areas.

Westerly preference is an important noise mitigation measure during the daytime. Aircraft taking off use more power than when landing and consequently make more noise. As most aircraft also take off at a steeper gradient than the 3° final approach glideslope followed by landing aircraft, take-off noise footprints are usually larger than landing ones, so their noise affects more people. However, the quid pro quo for reducing take-offs over west London is that landing aircraft have to make their final approach over London more often, and these are concentrated on the two final approach tracks."

Westerly preference doesn't operate at night, by the way.

[Gonzo]

Betterfromabove,

The westerly preference during a 5kt tailwind only applies when the runway is dry, and when the crosswind component is less than 12kts.

The hangars to the east of LHR do cause problems during strong crosswinds, this would not be reason to change ends in and of itself, but we may well de-alternate if needed - i.e. we would change to 27L for landing in a southerly crosswind.

[betterfromabove]

Gonzo.

Interesting. Reason I ask is that in terms of how Central-West London, where most of the population lies, is affected by noise, westerlies are definitely worse than easterlies....

....the poor residents of Hounslow notwithstanding, who get their fill either way!

PS. LHR and LCY on opposing r/w last night. Great view of an Emb145 turning over London Eye into LCY underneath us as we came in on 27L. Shame didn't have camera with zoom lens on me!

[DaveReidUK]

Reason I ask is that in terms of how Central-West London, where most of the population lies, is affected by noise, westerlies are definitely worse than easterlies....

The CAA don't seem to think so. When they modelled the effects of replacing westerly preference with an easterly preference, the conclusion was that it would move the noise contour lines such that they would enclose a greater proportion of the population.

I guess that's why westerly preference continues.

[betterfromabove]

Hmmh, odd.....

In all central and western boroughs, noise is substantially worse on westerlies, especially if living in Hamm+Fulham, Richmond, Barnes Ken+Chelsea and anywhere central, S of the river. It's even noticeable as far out as Islington/Tottenham.

I live in Hammersmith now, and when on easterlies, there is practically no noise whatsoever from Heathrow.

The newer types have definitely reduced the magnitude of the noise this past few years. Would say it's mainly Putney/Richmond and further west which really suffer on westerlies.

Footprint was worse in times gone past, esp. with the old Russian types, cargo 707's and the odd Concorde ;). Ah, those were the days, when the approach was actually interesting to look at....

[DaveReidUK]

In all central and western boroughs, noise is substantially worse on westerlies, especially if living in Hamm+Fulham, Richmond, Barnes Ken+Chelsea and anywhere central, S of the river. It's even noticeable as far out as Islington/Tottenham.

I live in Hammersmith now, and when on easterlies, there is practically no noise whatsoever from Heathrow.

No argument there.

But when LHR changes from westerlies to easterlies, the noise from arrivals and departures doesn't disappear, it just moves somewhere else.

The reason Central London doesn't hear easterly departures is that none of the 09 SIDs/NPRs go due east. Dover departures go out over Twickenham and Wimbledon, SAMs and MIDs over Molesey and Esher, and BUZAD/BPKs over Ealing.

I assume that those are the routes the CAA took into account in their modelling.

http://www.caa.co.uk/docs/33/ERCD0705.pdf