Winds & Runway in use

[Kirk Biddlecombe]

Why is it that sometimes, the opposite Runway to the wind will be used. At EGLL last night the winds were 040 @ 04Kts yet the 27's were being used...

[SilentHandover]

Most airports have a preferential runway, I believe Hounslow stay on westerlies up to a certain tail wind component that I am sure Gonzo et al will be more specific with.

[SilentHandover]

Runway 27 is on an approximate heading of 270 degrees so a wind on 040 would be a slight tailwind.

[Kirk Biddlecombe]

040, would mean the degree where the wind is coming from, or so I am assured.

Kirk

[eyeinthesky]

In order to pacify the nimbys, most large airports will operate a preferential runway system to minimise noise disturbance.

Heathrow was 27 as the preferred runway direction subject to a tailwind limit (10 knots I think), a crosswind limit, dry runway etc as you say. Gonzo will have the proper words ingrained on his memory!

Bournemouth has 26 as the preferred arrival runway but 08 as the preferred departing runway. I suppose you choose which you have more of before you commit!

Also, the runway numbering reflects its magnetic direction closest to the nearest 10 degrees, with the final 0 left off. So runway 27 is pointing approximately 270 degrees magnetic. A surface wind FROM 040 degrees magnetic (which is how it is reported) would be a combination of tailwind and crosswind in this case.

[Gonzo]

SH is correct. If the runway is dry, and the crosswind is below 12kts, we can stay on 27L/R up to a tailwind component of 5kts.

[foghorn]

LL went on to Easterlies later on last night, back on Westerlies by this morning.

[HEATHROW DIRECTOR]

<<Basically getting my lefts and rights (ie. 090 and 270)>>

Err...Blueskyrich... left and right has nothing to do with 090 and 270. At Heathrow there are 09L & 09R and 27R & 27L. 090 and 270 are the directionns of the runways and the L and R are left and right as you view them in the direction of landing and take-off. You need to mug up a bit so best of luck next month.

[HEATHROW DIRECTOR]

<<(ie. 090 on the 'right', 270 on the 'right').>>

I'm beginning to feel for you Blueskyrich! Always re-read what you've written, especially in exams. Don't even think of 270 being "left" and 090 being "right" (if that's what you mean). If you're heading south that idea falls apart.

[anotherthing]

Kirk

to amplify eyeinthesky

It's not just major airports that have preferred runways - as far as the UK is concerned it would be about 90% of airports at least.

Westerly runways are generally preferred in the UK due to the predominantly westerly prevailing winds. Smaller airports that do not have much money hedge their bets and have better facilities for the westerly runway than the easterly one (if money is an issue).

The amount of times we have westerly operations is far greater than easterly ones (watch me eat my words as a high pressure system starts to build this weekend).

As Gonzo stated, there are limits in place for wet and dry runways with regard to a crosswind and/or tailwind limit... this depends on the airfield (runway length, type of aircraft operating etc).

For example, some military airfields that mainly operate only 2 or 3 types regularly, may have vastly different crosswind criteria than some large civil airfields.

The length of runway also makes a difference with crosswinds if the A/C can keep up a higher speed on final approach (with more tarmac ahead to brake on on a longer runway) - this cuts down the effect the crosswind component has - again, more prevalant at military airfields than the larger civil ones.

[wiccan]

At Manchester, we are allowed a tailwind "component" of 5 knots. So surface wind 060/05 is accepted for r/wy 24. BUT if the 1000ft wind is 060/15+ then 06 will be used. It's a compromise between placating the neighbores....and safety.
bb

[Kirk Biddlecombe]

Thanks for the info!

[computer jockey]

I'd like to ask a further question, if I may...

A couple of replies to the original post made mention of tail wind and crosswind components. Am I right in assuming that these are vector components of the total wind speed?
So if we had wind 04kts at 045, the tail wind component would be 02kts and the crosswind component would be 02kts? Or is my maths all screwed up??

Thanks

cj - feet on the ground, head in the clouds and fingers on ctrl-alt-del.

[Gonzo]

CJ, you're correct.

[Kirk Biddlecombe]

Following on from what CJ said, if there was a wind 045 degress @ 04Kts, it's split 2 and 2 crosswind/tailwind respectively but, which direction is the crosswind and the tailwind coming from. Would the wind being given be a readout half way between these degrees? Or is my maths screwed up?

Kirk

[Spitoon]

Kirk, in the example you give the wind speed and direction and speed are always going to be the wind speed and direction and, certainly in the UK civil world, this is what the controller will pass to the pilot. The tailwind and crosswind components are 'theoretical' effects that the wind will have from directly behind or from 90 decrees to the side of the aircraft.

Hope this helps..........but now that I read what I've just typed I'm not sure!!

[Kirk Biddlecombe]

Hope this helps..........but now that I read what I've just typed I'm not sure!!

Well if you are right then it does make sense, thanks! :ok:

Kirk

[computer jockey]

Kirk,

The wind is always coming from 045 degrees, but if you imagine yourself in a plane sitting on runway 27, facing 270 degrees; 50% of the wind would be classified as tail wind and 50% classified as cross wind, but would still be called 045 deg @ 4 kts. If the wind was coming from 360 (or 0?), it would be 100% crosswind, if from 090, it would be 100% tailwind.

Gonzo - thanks for the confirmation


cj

[Gonzo]

Kirk, here's how you calculate a crosswind component:
For example, runway 27L, wind 300 degrees, 20kts.
Headwind component of 17.5 kts.
Crosswind component of 10 kts.

http://www.avweb.com/newspics/callthewind_wind_figure2.gif

[Kirk Biddlecombe]

Ah, fantastic! Thanks Gonzo!

Kirk

[Report@Boddam]

At Sumburgh the crosswind component can make for some very sporty landings during our long windy winter. Especially at night with a 40knot+ northerly when the only option is rw09/27. Not for the faint hearted.:}