Gusts

[hetfield]

Funny, flying for so long and still have to learn....

Example: 24015G27KT

To which direction do the gusts belong?

Thx

[BOAC]

If you guys are really serious -"flying for so long! :sad: it is 240, but wind in a gust normally veers, so you might expect, say 250-260

[hetfield]

Okay BOAC,

what about this:

Say you would like to depart from 27L/R EGLL and the wind is 27010G20kt, are you assuming tailwind?

[BOAC]

Did I see you two on 'Britain's Got Talent'?

[TopBunk]

I would suggest that it depends on the hemisphere.

In the Northern Hemisphere the gusts tend to veer, ie increase in value, eg 270/10G20 will likely see the gust to be from greater than 270 (maybe 300).

In the Southern Hemisphere the gusts tend to back, ie increase in value, eg 270/10G20 will likely see the gust to be from less than 270 (maybe 240).

[OutsideCAS]

....i'd suggest a spot of trolling is occurring here !!

[hetfield]

....i'd suggest a spot of trolling is occurring here !!Well everybody has his own point of view....

Maybe page 24 of this report

http://www.bfu-web.de/cln_005/nn_223532/EN/Publications/Investigation_20Report/2008/Report__08__5X003__A320__Hamburg-Crosswindlanding,templateId=raw,property=publicationFile.pdf/Report_08_5X003_A320_Hamburg-Crosswindlanding.pdf

...Variations from the mean wind speed (gusts) are preceded by „G“ and are reported as under 1.1.1.2.
Gusts will be reported if during the average time interval the maximum wind speed (peak gust) exceeds
the mean wind speed by at least 10 kt. To determine the peak gust, the 3-second average of the wind
speed is used. For gusts no direction is given. [ …]...

will make you think....

[dusk2dawn]

1:08 of pure suspense!

[aterpster]

hetfield:
Funny, flying for so long and still have to learn....

Example: 24015G27KT

To which direction do the gusts belong?
I'd vote for Miss Direction.

[latetonite]

Hetfield, you must have experienced some short and hard landings in your long career..

[Pugilistic Animus]

I guess the direction from which the wind blows...:)

[FlightDetent]

hetfield: If I read your post correctly, your question is "how does a pilot tell whether or not is gust direction significantly different from the prevailing wind?"

The answer could be hidden somwhere deep in my MET notes or Annex3, both of which are outside reach now. I suppose it would be coded as 27015kt 190V330G28 then. If it is plain simple 24015G27 the criteria to include the variating direction code had not been met, i.e. the measured gusts are "reasonably" close to the prevailing direction. What do you think?

Sincerely,
FD (the un-real)

PS: One station on our network regularly reports something like V5G18mps; funny how this causes havoc during preflight to stay legal for dispatch, especially on contaminated runways.

[hetfield]

@FD

Well, according to mentioned report, gusts are not close to the prevailing direction.

So, x-wind and tailwind limits can be easily exceeded!

[BOAC]

Hetfield - for one who has been 'flying so long' I am amazed!

Firstly your page ref is wrong - it is 20 not 24. A quick look at the paragraph above your quote shows EXACTLY what I said in my first post:

"Given a generally smooth land surface area, when the wind blows strong and the weather is stormy, the most powerful gusts blow in the same direction as the wind above the boundary layer. In the northern hemisphere the wind veers clockwise about 10° to 20° with respect to the mean wind direction."

What is the problem? Oh, and how do you get a tailwind out of 270/10-20 on Runway 27?. This is why 'trolls' were mentioned by OCAS and explains my reply:ugh:

[RAT 5]

Ladies, Please: back to aviation.

A/C type irrelevant; limtations. Rwy 26.

1. X wind = all X-wind + 1/2 gust; max 15 for autoland. W/V = 000/12G22. Can you land; do you ask the wind when at 200'agl (CAT 1 DA), does the gust veer to reduce the x-wind gust? Same argument for man' landing with greater numbers.
2. Tailwind. limit is 10kts. W/V 090/8G15. Can you land; ask the wind at 200agl?

Performance planners use 1/2 headwinds and 1.5 tailwinds for landing performance. I am asking about a/c limitations. There is nothing written down; Flt Ops have no idea and give no guidance. It is a grey area in an area of limitations. Do you divert with commercial consequences? Do you be a hero and land? Do you land, slide off the end, lose you licence and get fired? Staggeringly it is impossible to find a definitive answer from the powers that be. It is a safety and commercial issue, yet taken so 'unseriously' by managements.
Advices and opinions? Even better, any hard facts, especially EU ops?

[BOAC]

Oh goody! Back to aviation.

X wind = all X-wind + 1/2 gust; - in my books, gusts have to be 'considered', no '50%'

Can you land - yes

do you ask the wind when at 200'agl - probably not if it is on my nav display

does the gust veer to reduce the x-wind gust? - in your example, yes (probably), and increase the tailwind

Same argument for man' landing with greater numbers.
2. Tailwind. limit is 10kts. W/V 090/8G15 - again yes (will have had a shufti at the runway performance, mind you):O

ask the wind at 200agl? - again probably not

[Nubboy]

Ah, a debate at last;)
The best I could get from our flight safety department was that the tower reported wind takes precedence over other sources, including the little green arrow in the corner of your ND.

The rationale for this is that the info you have on IRS drift is not definitive enough to override any authorised reports, which the tower wind is (or should be). Plus it's the wind at the threshold that counts, not DH, MDA or anything else. (In the middle of nowhere, in the middle of the night, I suggest we all go very carefully in this age of instant expert analysis and litigation.)

[A321COBI]

I dont mind turbulence on my plane but gusts are the worst possible thing to have
I was landing my A321 plane the other day, perfectly lined up on a clear day and then suddenly a strong gust of wind blew the aircraft straight of course which takes an awfull lot and I spent another 15 minutes attempting it again [this time succesful]

[hetfield]

@Boac
Firstly your page ref is wrong - it is 20 not 24. A quick look at the paragraph above your quote shows EXACTLY what I said in my first post:

"Given a generally smooth land surface area, when the wind blows strong and the weather is stormy, the most powerful gusts blow in the same direction as the wind above the boundary layer. In the northern hemisphere the wind veers clockwise about 10° to 20° with respect to the mean wind direction."If I open the pdf, it's 24/85.
However I don't want't to put the discussion to that low level....


Further on the report (24/85): For gusts no direction is given. [ …]

Regards

[TopBunk]

Tailwind. limit is 10kts. W/V 090/8G15. Can you land; ask the wind at 200agl?


As a general principle, don't ask a question in case you get an answer you don't want:hmm:

[BOAC]

Yes, yes, yes, but did you read it?

Supplementary - so how do you get a tailwind out of it?

[hetfield]

BOAC

If no direction is given, one has to assume a tailwind out of it, don't you?

[BOAC]

I take it that is your way of saying you did not read ALL of Seite 20?

[hetfield]

BOAC

If you are referring to the passage

"Given a generally smooth land surface area, when the wind
blows strong and the weather is stormy, the most powerful gusts blow in the same direction as the wind
above the boundary layer. In the northern hemisphere the wind veers clockwise about 10° to 20° with
respect to the mean wind direction. These assumptions do not hold good in hilly terrain, thunderstorms,
thermal weather conditions, during the passage of fronts and so forth."

Yes, I've read it:rolleyes:

And that's exactly what my question is about!

Cheers

[FlightDetent]

Ok, the behaviour of gust (whatever we think it is) is established. The actual conditions will get measured and reported. Here's what the coding should look like, Annex 3 [my bolding]:
4.1.3 Averaging
4.1.3.1 The averaging period for surface wind observations shall be:
a) 2 minutes for local routine and special reports and for wind displays in air traffic services units; and
b) 10 minutes for METAR and SPECI, except that when the 10-minute period includes a marked discontinuity in the wind direction and/or speed, only data occurring after the discontinuity shall be used for obtaining mean values;
hence, the time interval in these circumstances should be correspondingly reduced.

Note.— A marked discontinuity occurs when there is an abrupt and sustained change in wind direction of 30° or more, with a wind speed of 20 km/h (10 kt) before or after the change, or a change in wind speed of 20 km/h (10 kt) or more, lasting at least 2 minutes.

4.1.3.2 Recommendation.— The averaging period for measuring variations from the mean wind speed (gusts) reported in accordance with 4.1.5.2 c) should be 3 seconds for local routine and special reports and for METAR and SPECI and for wind displays used for depicting variations from the mean wind speed (gusts) in air traffic services units.
4.1.5 Reporting
4.1.5.2 In local routine and special reports and in METAR and SPECI:
....
b) variations from the mean wind direction during the past 10 minutes shall be reported as follows, if the total variation is 60° or more:
_1) when the total variation is 60° or more and less than 180° and the wind speed is 6 km/h (3 kt) or more, such directional variations shall be reported as the two extreme directions between which the surface wind has varied;
_2) when the total variation is 60° or more and less than 180° and the wind speed is less than 6 km/h (3 kt), the wind direction shall be reported as variable with no mean wind direction; or
_3) when the total variation is 180° or more, the wind direction shall be reported as variable with no mean wind direction;
c) variations from the mean wind speed (gusts) during the past 10 minutes shall be reported when the maximum wind speed exceeds the mean speed by:
_1) 10 km/h (5 kt) or more in local routine and special reports when noise abatement procedures are applied in accordance with paragraph 7.2.3 of the PANS-ATM (Doc 4444); or
_2) 20 km/h (10 kt) or more otherwise;4.1.5.3 In local routine and special reports:
...
c) when variations from the mean wind direction are reported in accordance with 4.1.5.2 b) 2), the two extreme directions between which the surface wind has varied shall be reported; and
d) when variations from the mean wind speed (gusts) are reported in accordance with 4.1.5.2 c), they shall be reported as the maximum and minimum values of the wind speed attained.
4.1.5.4 In METAR and SPECI, when variations from the mean wind speed (gusts) are reported in accordance with 4.1.5.2 c), the maximum value of the wind speed attained shall be reported.

hetfield: Based on above I think the BFU report is not 100% sincere with regards to wind shear reporting and coding. What we had been discussing under gust is in fact wind shear i.e. change in speed and direction. However, for Annex 3, the term gust is used for windspeed change only and varying direction, if any, is dealt with separately.

Therefore 24015G27KT
- is a METAR/SPECI code based on 10 minute average (no min speed provided);
- indicates windspeed change with direction less than 60 deg from average; the direction change (if any) associated with gust is already calculated into the average direction reported as 240;
- the observed conditions may by extreme (my approximation) be: steady 220/10 with wind shears 260/27;

It's all academic and complicated but it serves one purpose, to provide pilots with reliable numbers. If I would like to depart from 27L/R EGLL and the wind is 27010G20kt I would assume true conditions 250/6 gusting 280/20 based on the fact that rules to include varying code into the wind (60 deg offset from average) report had not been met. To summarize, if no varying component is reported, the measured gust is "reasonably" close to the wind direction provided.

Sincerely,
FD (the un-real)

[hetfield]

Thx FD for clarification:ok:

That's exactly what I'm looking for.

Fly safe:)