Crosswind calculation with gust factor.
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Crosswind calculation with gust factor.
Good day all!
How do you calculate a crosswind, with wind gust factor?
Rwy 03, wind 090/25 gusting 40 kts.
Thanks in advance!!!
How do you calculate a crosswind, with wind gust factor?
Rwy 03, wind 090/25 gusting 40 kts.
Thanks in advance!!!
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( x-wind component 39.9 kts from the right with a HWC of 1.3 kts ) Simples
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Crosswind gusts are a bit of a gray area in the rules. The Boeing FCTM even implies that crosswind limits are a guide only, and not a strict limitation. On the day, it is down to the commander to decide if a landing may go ahead, subject to the guidance limitations in his Operations Manual.
A gust is only a short duration peak of the wind. Therefore the vast majority of time is more at the stated wind. The stated wind is what guides you on whether you may complete the approach, the actual threshold wind just before landing is what guides you whether you may complete the landing. It is overwhelmingly likely that your landing will take place at times when the wind is not gusting. Therefore, you may assume the wind is 090/25 and rely significantly on your own judgement. The gust figure is to guide you, not in this case to set a limitation on landing.
But if you include the gust figure, I make that a mental calculation of 35 kts, so I would forget iPhone applications in this case and rely on your brain! The HWC comes to 20kts (gust figure). That's the trouble with computers- rubbish in, rubbish out!
So, just use standard wind, and bear in mind gust factor, but don't let it spoil your day. And you have to have these figures mentally:
Wind/Track angle/Crosswind Factor/Headwind Factor
15............25%/97%
30............50%/87%
45............70%/70%
60............87%/50%
75............97%/25%
Learn it so you can reproduce it with one engine out, stewardess passing you coffee over your shoulder and copying Volmet at the same time!
A gust is only a short duration peak of the wind. Therefore the vast majority of time is more at the stated wind. The stated wind is what guides you on whether you may complete the approach, the actual threshold wind just before landing is what guides you whether you may complete the landing. It is overwhelmingly likely that your landing will take place at times when the wind is not gusting. Therefore, you may assume the wind is 090/25 and rely significantly on your own judgement. The gust figure is to guide you, not in this case to set a limitation on landing.
But if you include the gust figure, I make that a mental calculation of 35 kts, so I would forget iPhone applications in this case and rely on your brain! The HWC comes to 20kts (gust figure). That's the trouble with computers- rubbish in, rubbish out!
So, just use standard wind, and bear in mind gust factor, but don't let it spoil your day. And you have to have these figures mentally:
Wind/Track angle/Crosswind Factor/Headwind Factor
15............25%/97%
30............50%/87%
45............70%/70%
60............87%/50%
75............97%/25%
Learn it so you can reproduce it with one engine out, stewardess passing you coffee over your shoulder and copying Volmet at the same time!
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hello all, just two things:
a crosswind limit is only a demonstrated one. The test pilots showed it could be flown at that crosswind speed. the a/c manufacturer only states the demonstrated maximum. it's then up to your company sop to determine if it's a strict limit or not (it most usaually is)
there's been a change a few years ago concerning crosswind limit. the old rule for certification was xx kts gust not included. now it's stated as xx kts gust included.
example: older a320 was (if i remember correctly) 33 kts gust NOT included so if the tower gave you a wind of 32 gusting 65 you could still land and stay within your sop. on the 777 (a newer bird) the limit is 38 kts gust included. so, in the same conditions, sop would not allow you to land.
seb
a crosswind limit is only a demonstrated one. The test pilots showed it could be flown at that crosswind speed. the a/c manufacturer only states the demonstrated maximum. it's then up to your company sop to determine if it's a strict limit or not (it most usaually is)
there's been a change a few years ago concerning crosswind limit. the old rule for certification was xx kts gust not included. now it's stated as xx kts gust included.
example: older a320 was (if i remember correctly) 33 kts gust NOT included so if the tower gave you a wind of 32 gusting 65 you could still land and stay within your sop. on the 777 (a newer bird) the limit is 38 kts gust included. so, in the same conditions, sop would not allow you to land.
seb
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And some ops manuals don't mention it! I guess the best answer is....follow the instructions in your ops manual! But, what is most important- that wind just before landing- know how to mentally work out crosswind component if you want to keep yourself out of trouble! Try whipping out your iPhone to work out crosswind components at 200'! No future in that at all!
Rainboe take care with definitions “A gust is only a short duration peak of the wind” (#3).
The authors of ‘Safety aspects of aircraft operations in crosswind’ define, with good reason, a gust as “Substantial deviations of the mean wind speed over a time period”. The method of reporting filters the higher frequency peaks in wind speed which are less relevant to performance, which in many cases pilots use to support a decision to reduce or to discount gusts. Note in fig 4 that the maximum reported wind speed (gust) is not the same as the actual and higher maximum wind speed. Furthermore I don’t see that the report supports a conclusion that when landing it is ‘overwhelmingly likely’ that a gust would not be encountered. Page 15 – 16:
See fig 13, where the crosswind includes the gust; the risks during landing increase rapidly above 15kts. The crosswind accident rates are shown in fig 14, again including gusts.
From the conclusions:-
“Adhere to the Ops Manual” – yes, but check that the advice is based on fact.
The authors of ‘Safety aspects of aircraft operations in crosswind’ define, with good reason, a gust as “Substantial deviations of the mean wind speed over a time period”. The method of reporting filters the higher frequency peaks in wind speed which are less relevant to performance, which in many cases pilots use to support a decision to reduce or to discount gusts. Note in fig 4 that the maximum reported wind speed (gust) is not the same as the actual and higher maximum wind speed. Furthermore I don’t see that the report supports a conclusion that when landing it is ‘overwhelmingly likely’ that a gust would not be encountered. Page 15 – 16:
Overall it can be concluded from the example, that a reasonable probability does exist, that while wind reports to the pilot do indicate that crosswind is not exceeding 15 Kt, in reality the actual encountered crosswind during the landing phase can deviate 10 Kt or even more from the reported wind. For even higher reported crosswinds, deviations may increase accordingly.
From the conclusions:-
Gusty wind is the most important contributing factor in crosswind-related accidents and incidents. It can be noted that the strength of the gustiness depends mainly on the total wind, which can be much stronger than the crosswind component itself. The probability of the occurrence of a crosswind related accident increases with increasing crosswind conditions. Statistical evidence, based on historic accident data, shows that the accident risk increases exponentially when operating in conditions with crosswind exceeding 20 Kt, including gust.
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Well I guess you must be diverting quite a lot and never facing strong crosswinds if they are so risky! I have known 40 kt crosswinds. On the day, it comes down to the winds you get from the tower approaching the threshold and your own judgement, within the constraints of the Ops Manual. It is very much left to the discretion of the Captain on the day. With a lot of experience, even a strong gusty crosswind, in the right hands, is not a problem. That is why I wince when I hear of the 'superpilots'- captain of a 747 at 27 years of age, or a 737 captain at 24. I have seen weather that is unbelievable. I doubt whether they have had the experience to experience such conditions enough. Fine, if their judgement is good enough to make the right decision to GA at the right time. We have in our team pilots coming up who regularly now bang off limiting crosswind landings in one of the world's windiest places- Iceland. An email I received a couple of weeks ago
The runways are 10 and 19. We're doing this as a normal operation every day, safely and regularly. The guys are getting terrific experience and are becoming the best in the air. So I'm really not very impressed with your
Sorry, but our guys and banging 'em out several times a day in that (and I do apologise, even one lady as well)! Come and get some hairs on your chest!
Look at your graph of wind on page 13. I repeat, <<a gust is only a short duration peak of the wind>> The wind is what the tower gives you, gusts are short term peaks over a period. What hope do we have of defining crosswind limits if people are going to quibble over a definition like this? As as for including gusts fully in a crosswind limit, all I can say is 'move over- there are thousands willing to do your job properly!'
...You will be amused to hear that the wind on Sunday was 160/50G60....a very sporty approach!! We love it here!
See fig 13, where the crosswind includes the gust; the risks during landing increase rapidly above 15kts.
Look at your graph of wind on page 13. I repeat, <<a gust is only a short duration peak of the wind>> The wind is what the tower gives you, gusts are short term peaks over a period. What hope do we have of defining crosswind limits if people are going to quibble over a definition like this? As as for including gusts fully in a crosswind limit, all I can say is 'move over- there are thousands willing to do your job properly!'
Last edited by Rainboe; 24th Nov 2009 at 20:34.
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Good to see the landings are improving and the lady has hairs on her chest.
TCAS - the simple answer to your question is to look at an analogue clock face and that will give you the angle factor. Your example would be 12 1/2 across gusting a bit over 20, since in the northern hemisphere the wind generally veers in gusts, so that Icelandic 160/50-60 is well under the 737 max demonstrated at 25 gusting 28 ish. A mere zephyr. Hardly enough to dislodge a toupee.
TCAS - the simple answer to your question is to look at an analogue clock face and that will give you the angle factor. Your example would be 12 1/2 across gusting a bit over 20, since in the northern hemisphere the wind generally veers in gusts, so that Icelandic 160/50-60 is well under the 737 max demonstrated at 25 gusting 28 ish. A mere zephyr. Hardly enough to dislodge a toupee.
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And as I don't have time to get my iPhone out on approach, for anyone who doesn't know (and/or who wants an easy way to do it whilst hand flying and trying not to take up too many grey cells!):
1/2 the reported wind if its 30 degrees off = the crosswind (1/2,3)
2/3 the reported wind if its 40 degrees off = the crosswind (2/3,4)
3/4 the reported wind if its 50 degrees off = the crosswind (3/4,5)
...and any more than that its pretty much all crosswind (apparently).
I was shown this years ago in a Cessna 152 and have used it in everything from a Cirrus to a heavy jet and it is surprisingly accurate.
Gust factor = respect the maximum wind speed, I reckon, even if it's a gust !
1/2 the reported wind if its 30 degrees off = the crosswind (1/2,3)
2/3 the reported wind if its 40 degrees off = the crosswind (2/3,4)
3/4 the reported wind if its 50 degrees off = the crosswind (3/4,5)
...and any more than that its pretty much all crosswind (apparently).
I was shown this years ago in a Cessna 152 and have used it in everything from a Cirrus to a heavy jet and it is surprisingly accurate.
Gust factor = respect the maximum wind speed, I reckon, even if it's a gust !
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1/2 the reported wind if its 30 degrees off = the crosswind (1/2,3)
2/3 the reported wind if its 40 degrees off = the crosswind (2/3,4)
3/4 the reported wind if its 50 degrees off = the crosswind (3/4,5)
...and any more than that its pretty much all crosswind (apparently).
2/3 the reported wind if its 40 degrees off = the crosswind (2/3,4)
3/4 the reported wind if its 50 degrees off = the crosswind (3/4,5)
...and any more than that its pretty much all crosswind (apparently).
50 degrees off is .75 of the stated windspeed <<and any more than that its pretty much all crosswind (apparently)>> No it isn't? You are in error by up to 25% of the stated windspeed!
60 degrees is 87%
75 degrees is 97% (now we are getting to 'pretty much all crosswind').
You can be easily in error your way by up to about 20% of the wind, which for a 40kt crosswind limitation could see you having to go around because of an error you have made in your calculation of 8kts when you could legally have landed! My suggested method above is highly accurate- all it takes is learning a few numbers! It will give you bang on the actual crosswind, not a poor approximation.
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Without having to learn any numbers, there is an easy way of determining the individual components:
Crosswind = Reported windspeed x (angle + 20)/100
an example:
RWY 21
W/V 250/30
X = 30 x (40 + 20) / 100 = 18kn
Headwind = Reported windspeed x ((90 - angle) +20)/100
X = 30 x ((90 - 40) + 20) / 100 = 21kn
Try it a few times and you will find this an easy tool without paper and pen required.
Check accuracy below:
Worked for me for more than 30 years....
Crosswind = Reported windspeed x (angle + 20)/100
an example:
RWY 21
W/V 250/30
X = 30 x (40 + 20) / 100 = 18kn
Headwind = Reported windspeed x ((90 - angle) +20)/100
X = 30 x ((90 - 40) + 20) / 100 = 21kn
Try it a few times and you will find this an easy tool without paper and pen required.
Check accuracy below:
Worked for me for more than 30 years....
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information on crosswind certification
More information on crosswind certification can be found in this paper:
http://www.nlr.nl/id~5114/lang~en.pdf
http://www.nlr.nl/id~5114/lang~en.pdf
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I'm with dontdoit.
The "clock code" calculation of crosswinds has served me well for decades. I discussed it with my grandfather recently (an RAF WW2 night-fighter ace and QFI) and he could even recall the principle.
15 degrees off = 15 out of 60 minutes is a quarter so 25% of the wind velocity
20 degrees off = 20 out of 60 minutes is a third so 33% of the wind
30 degrees off = 30 out of 60 minutes is half, so 50% of the wind
45 45 75%
60 60 100%
This is slightly conservative, but who cares on short finals. Crosswind limits are maximum demonstrated.
This makes life very easy where your F/O maximums are concerned, since you are primed to take over earlier than the more complicated calculations.
For the actual landing, you can go into the decision more conservatively minded
The "clock code" calculation of crosswinds has served me well for decades. I discussed it with my grandfather recently (an RAF WW2 night-fighter ace and QFI) and he could even recall the principle.
15 degrees off = 15 out of 60 minutes is a quarter so 25% of the wind velocity
20 degrees off = 20 out of 60 minutes is a third so 33% of the wind
30 degrees off = 30 out of 60 minutes is half, so 50% of the wind
45 45 75%
60 60 100%
This is slightly conservative, but who cares on short finals. Crosswind limits are maximum demonstrated.
This makes life very easy where your F/O maximums are concerned, since you are primed to take over earlier than the more complicated calculations.
For the actual landing, you can go into the decision more conservatively minded
The runways at KEF are actually 11 and 20. Winds of 150-160(M) at 50-70 are not uncommon during winter, right between the runways. It can be a real toss up which one to use. In addition the windsensors are somewhat badly placed as buildings appear to create disturbances affecting them, and also aircraft on short finals.
It has served me well in windy and gusty situations all over the world, to keep the FMC on PROG II (757/767) and take a peek at the crosswind occasionally, it will normally give you a fairly stable wind indication to base your descision whether to land or not in limiting situations.
It has served me well in windy and gusty situations all over the world, to keep the FMC on PROG II (757/767) and take a peek at the crosswind occasionally, it will normally give you a fairly stable wind indication to base your descision whether to land or not in limiting situations.
