Departure separation with strong crosswinds

[RJKflyer]

Taking off from LHR the other day, I noted a crosswind of 15-20 knots at 90 deg to the runway.

In an A319, we waited at 27R for a 744 to go, and the duration felt like a medium following heavy wake turbulence separation.

So, it felt like we waited for a 'normal' period - are there not reduced separations when crosswinds > 7kts (I think) are active?

(Obv as it was 27R - as opposed to 27L - we weren't influenced by landing vortices from the other parallel runway)

[Nicholas49]

Maybe this should be in the ATC / Questions forum?

[redED]

are there not reduced separations when crosswinds > 7kts (I think) are active?

No there aren't, there'd be too much is it, isn't it.

[HEATHROW DIRECTOR]

<<Obv as it was 27R - as opposed to 27L - we weren't influenced by landing vortices from the other parallel runway>>

As already mentioned, there is no such separation standard. However, I'm interested in the sentence above. What difference do you think it would it have made had you been on 27L?

[RJKflyer]

Well I am no expert, and what I am about to say is probably not the case at LHR as the two runways are separated by all sorts of clutter and a reasonable distance.

However, let me explain. Imagine:

1. Crosswind from the north
2. Taking off from 27L
3. Therefore landings on 27R

The landing vortices from 27R would be blown across 27L and have an impact on operations there. I seem to recall some Euro study on this?

"The study concentrated on Paris CDG airport where there are two CSPRs for departing and arriving aircraft. Departing aircraft on one of the runways had to join further down the runway to avoid wake turbulence from aircraft arriving on the adjacent runway"

[One9iner]

I'm sure Heathrow Director can put me right here, but from my ATPL training, wake turbulence separation doesn't really take crosswind component into effect when using the same runway. If you think about it, the stronger the crosswind, the more chance the vortices will be blown away from the centre line thus eradicating the issue.

It's all to do with weight. i.e. heavier the aircraft ahead, the more lift generated by the wings therefore potentially stronger vortices.

Also, during CPL training, if we were in a light twin at a busy airport, taking off behind a medium category jet, we would just ensure we were airborne before the rotate point of the aircraft ahead, as vortices won't come into effect until the aircraft is airborne.

"G-XXX, surface wind 240/10 RWY 27L cleared immediate take off" ...mmm they don't seem to be using any wake turbulence separation here Mr Instructor? "It's Ok, just get airborne before the point that 737 rotated, we'll be fine, just get on with it, there's a heavy up our chuff" ;)

[HEATHROW DIRECTOR]

RJKFlyer. At Heathrow, so far as I know, no account is taken of what you suggest. There is no reason to suggest that wake turbulence from landing aircraft on one runway could have any effect on the other runway. What mainly determines the runway configuration is noise abatement. Only in exceptional circumstances is the configuration varied - for example in a strong southwesterly wind the turbulence off the BA hangars may interfere with landings on 27R so the configuration may be changed..

[Talkdownman]

Tower Sup is the Final Arbiter but he/she must justify his/her departure from the published script to The Noise Police...

The landing vortices from 27R would be blown across 27L and have an impact on operations there
Wouldn't even blow a match out...

[Gonzo]

To be independent from a vortex point of view, ICAO states that parallel runways must be 760m or more apart. LHR's are 1415m apart.

As for reducing wake turbulence separation on departure due to crosswind, there is research being undertaken on the subject.

Eurocontrol ran a project called CREDOS EUROCONTROL - About CREDOS (http://www.eurocontrol.int/eec/credos/public/standard_page/about_CREDOS.html) a few years ago, and in the UK NATS are also doing preliminary work along similar lines.