Wind Information
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Wind Information
Hi all,
In strong winds what information source do you use to obtain surface wind info and at what point do you decide to land or go look for a better runway? Is ATIS information sufficient or would you rather wait for the Tower Wind given that this value is often more representative of the actual conditions at time of landing?
As an inexperienced student I’m still finding it difficult to make quick calculations of the surface crosswind conditions when the tower give me the wind vector (usually on final with landing clearance) as there seems to be so many other things to do! As such I tend to try and make the calculation early using the ATIS but im aware that this is a bad habit as this information could be dangerously outdated. Anybody had similar problems?
Regards
Low Fi
In strong winds what information source do you use to obtain surface wind info and at what point do you decide to land or go look for a better runway? Is ATIS information sufficient or would you rather wait for the Tower Wind given that this value is often more representative of the actual conditions at time of landing?
As an inexperienced student I’m still finding it difficult to make quick calculations of the surface crosswind conditions when the tower give me the wind vector (usually on final with landing clearance) as there seems to be so many other things to do! As such I tend to try and make the calculation early using the ATIS but im aware that this is a bad habit as this information could be dangerously outdated. Anybody had similar problems?
Regards
Low Fi
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You start with ATIS wind, then go onto tower wind. You must not land outside crosswind limits, so you cannot ignore any information or commit yourself too early. It's the one at touchdown that counts.
Work it out this way. Difference between runway heading and wind direction (to 10 degrees). Multiply wind speed by Sine of this figure, so memorise:
Sine 0 degrees = 0% (wind down runway, no crosswind)
Sine 15= 25%
Sine 30= 50%
Sine 45= 70%
Sine 60= 87%
Sine 75= 97%
So, a 25 knot wind blowing at 45 degrees to the runway, about 18 knots crosswind. You have to memorise that table, but it has carried me through 33 years on jets!
Work it out this way. Difference between runway heading and wind direction (to 10 degrees). Multiply wind speed by Sine of this figure, so memorise:
Sine 0 degrees = 0% (wind down runway, no crosswind)
Sine 15= 25%
Sine 30= 50%
Sine 45= 70%
Sine 60= 87%
Sine 75= 97%
So, a 25 knot wind blowing at 45 degrees to the runway, about 18 knots crosswind. You have to memorise that table, but it has carried me through 33 years on jets!
I was taught during my PPL training to use the clock face method to give a guesstimate of the crosswind component. That is:
15 mins = quarter of an hour
30 mins = half an hour
45 mins = three quarters
60 mins = whole hour
Therefore if the wind was up to 15 degrees off the runway heading, then the crosswind component is approx. one quarter of the given windspeed, 30 degrees = one half etc.
eg. Runway 27, wind 300/20 crosswind component = 10knots.
wind 280/20 crosswind component = 5knots.
15 mins = quarter of an hour
30 mins = half an hour
45 mins = three quarters
60 mins = whole hour
Therefore if the wind was up to 15 degrees off the runway heading, then the crosswind component is approx. one quarter of the given windspeed, 30 degrees = one half etc.
eg. Runway 27, wind 300/20 crosswind component = 10knots.
wind 280/20 crosswind component = 5knots.
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Thanks Guys,
Those approximation techniques are very useful. I must admit to having them explained to me before but didn't really understand. Having it written down makes it a whole lot clearer. I guess what I need to do is just practice, practice, practice!
Low Fi
Those approximation techniques are very useful. I must admit to having them explained to me before but didn't really understand. Having it written down makes it a whole lot clearer. I guess what I need to do is just practice, practice, practice!
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'Approximation technique'? Wash your mouth out with soap boy! Mine is spot on! The clock one is good, but a bit 'thick pencil'- I note the error is 5% at 45 degrees and 13% at 60 degrees wind track angles, but not bad if you are 'mental arithmetically' challenged!
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You're asking what headwind/tailwind component a crosswind will give? It is simply the second column upside down. All you have to do is remember the angles 15,30,45,60,75 and the factors to multiply of .25,.50,.70,.87,.97
So, on final approach you have a 20 kt wind at 30 degrees angle to the runway. The crosswind is .50 times that = 10 kts, and the headwind component is (reversing the second table) .87 times that = 17 kts. If you don't understand that, think of the triangle a wind makes with crosswind and headwind components. The wind track angle is measured at the aeroplane corner- the crosswind is obtained from the Sine and the headwind from the Cosine. So to switch the table, you just reverse the second 'factor' table above. All you have to remember is the order 25,50,70,87,97 and reverse it for head/tailwind 97,87,70,50,25. It's advantage is it is as exact as you can get without a computer with no inaccuracies.
So, on final approach you have a 20 kt wind at 30 degrees angle to the runway. The crosswind is .50 times that = 10 kts, and the headwind component is (reversing the second table) .87 times that = 17 kts. If you don't understand that, think of the triangle a wind makes with crosswind and headwind components. The wind track angle is measured at the aeroplane corner- the crosswind is obtained from the Sine and the headwind from the Cosine. So to switch the table, you just reverse the second 'factor' table above. All you have to remember is the order 25,50,70,87,97 and reverse it for head/tailwind 97,87,70,50,25. It's advantage is it is as exact as you can get without a computer with no inaccuracies.
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You see how very simple it is? - just memorise sine/cosine tables, and multiply winds by those figures while you're struggling with a large aeroplane in turbulence and crosswind and rain and lightning, with an engine out and the 'Jesus is that all the fuel we've got left?' light is on. It's called being an airline pilot! Some people think it is lying on a beach with a cold bird in yer hand!
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I think the key is to keep it simple. The clock method is the one that I use and it has never failed me.
The sin method proposed by Notso is undoubtedly very accurate, but does not strike me as the most user friendly and easiest way.
Notso, I agree that up to 13% errors are possible, but remember the amounts that we are talking about. 13% of typical figures is generally insignificant.
The sin method proposed by Notso is undoubtedly very accurate, but does not strike me as the most user friendly and easiest way.
Notso, I agree that up to 13% errors are possible, but remember the amounts that we are talking about. 13% of typical figures is generally insignificant.
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I have to agree. When all your functions are taken up elsewhere, it is about the limit of what you can handle.
However, I am Superman! Not for me 'approximations'! 13% error can be 3 knots (for mere mortals) and still invalidate the insurance for your aeroplane. There are limits (even for Superman) that you must not cross or it's kryptonite up your rear end! I shall continue using my convoluted way, but encourage everyone (who doesn't have super powers) to use your sensible and simple way!
However, I am Superman! Not for me 'approximations'! 13% error can be 3 knots (for mere mortals) and still invalidate the insurance for your aeroplane. There are limits (even for Superman) that you must not cross or it's kryptonite up your rear end! I shall continue using my convoluted way, but encourage everyone (who doesn't have super powers) to use your sensible and simple way!
