Working out the crosswind component

[Cactus99]

Had a search but couldn't find anything similar.

How does one work out the actual crosswind component whilst on final approach to land, given a wind direction and speed.

I'm sure I did this many moons ago whilst doing ATPLs, but can't for the life of me remember.

Thanks :ok:

[wiggy]

The Clock method? A rough rule of thumb that will annoy the pedants but:

Think of the degrees off the nose as portions of the hour,
so >= 60 degrees - 60 minutes - the whole hour - i.e. it's all crosswind
45 degrees - three quarters hours - three quarters is crosswind component.
30 degrees - 30 minutes - half hour - half is crosswind, etc, etc

Well, it's either that or remember your sine tables......:ooh::ooh:

[hvogt]

Hi Cactus99

You can calculate the crosswind component as follows:

XWIND = WIND SPEED * SIN (WIND ANGLE)

Example:

RWY 27, wind 300 degrees 20 knots. Wind angle is 30 degrees. Sine of 30 degrees is 0.5. Crosswind is 10 knots.

For mental calculations you obviously have to use rounded values for the sine function. I use:

SIN(0°)=0
SIN(10°)=0.2
SIN(20°)=0.3
SIN(30°)=0.5
SIN(40°)=0.6
SIN(50°)=0.8
SIN(60°)=0.9
SIN(70°)=0.9
SIN(80°)=1
SIN(90°)=1

As you can see the values are rounded amply. That way you're always on the safe side.

[handflown]

The clock code is the best by far.

If you can remember the sin values above then you are a better man than most. You obviously need to work out the x wind quickly with little effort to allow you to multi-task on the other things on you mind - like flying and landing the aircraft (or possibly a go-around).

[p7lot]

Calculating the crosswind is the sinus function of the wind angle, therefore another way to simply figure out crosswind is to know 4 sinus numbers. The 4 sinus numbers of 30, 50, 60, and 80 degrees.
sin30 = .5 (with a wind from 30 degrees the cwc is half the total wind)
sin50 = .75 (with a wind from 50 degrees the cwc is 3/4 the total wind)
sin60 = .9 (with a wind from 60 degrees the cwc is the total wind minus 10%)
sin80 = 1.0 (any wind of more than 80 degrees and your cwc is the total wind)
But by far the easier is the clock method

[handflown]

Another simple one to remember is how to calculate track miles to run.

Say you are tracking to a position to intercept an ILS. Or you are being vectored by air traffic.

You are tracking/being vectored towards this position at an intercept heading to then intercept and fly the localiser. You are taking a DME read out from the ILS facility but because you are flying at an intercept heading before then flying staight to the facility you know your actual track miles is longer.

To work out the track miles to run just remember these 3 values.

30 degrees .9
60 degrees .75
90 degrees .5

For example
The runway and therefore ILS is 090 degrees for runway 09.
You are flying on a heading of 180 degrees to the 10 mile fix. Your DME read out on the 180 hdg is 10 miles. However you are slightly north west of the runway at this stage and not tracking directly to the runway you are going to intercet the 090 QDM at the 10 mile fix. A 180 hdg is a 90 degree intercept. 90 degree equals .5. If 10 mile dme is .5 you must double this to make 1. Eg the track miles to run is 20 miles.

Similarly a 60 degree intercept equals .75. So a 10 mile dme reading would mean you are 13.3 miles to run.

30 degree intercept equals .9. Therefore with 10 mile dme equals 11.1 miles.

Try this. I think the values I have used are pretty acurate but there may be some more scientificly minded people out there whom can correct me. I find the above has worked well for me as a rule of thumb when calculating descent profiles.

[OSCAR YANKEE]

Way back when.......MDR (Mental Dead Reckoning) was obligatory stuff for the ATPL back home. (Denmark). Allways thought everybody did this ?

Getting lazy on my older days, I simply ask the tower if its close to limits. ;)
(ie. "Request Crosswind")
Most towers have it on display on the wind readout thing all the time.......

Rgds. OY

[Cactus99]

Very helpful, thanks for all the replies chaps, big help!! :ok:

[smith]

Always wondered why don't say "cleared to land, cross wind component xxkts" instead of "cleared to land, surface wind xxx/xxkts"?

[james ozzie]

Always wondered why don't say "cleared to land, cross wind component xxkts" instead of "cleared to land, surface wind xxx/xxkts"?

Presumably to leave responsibility clearly with the pilot? They don't want a situation where a landing exceeding limits is blamed on the ATC messing up his vector addition?

[Willit Run]

most crosswind limits, are not really limits, they are "demonstrated" limits. If you can demonstrate a new limit, go for it.
However, if you have a malfunction, i.e. partial flap, no in flight spoilers, multiple hydraulic failure, and so on, and are now limited to a 20 knot limit, thats a "hard" limit. I've seen many a pilot demonstrate a landing that was over the demonstrated limit in the book.

Many of these pilots had several/many thousand hours as PIC in the planes which was significantly more than than the test pilots had when demonstrating the limit.

[Leave 5 on the glide]

Guys/Girls,

The other way to do it is to work out the crosswind component by using the wind speed multiplied by the sine of wind angle off of the A/c heading. The sine of the wind angle can be found by taking the angle, dropping the zero, dividing by 10 and adding 0.2.

E.g. W/V 120/12, A/c heading 150.

=> W/V is 30 off A/c heading:

X-wind component = 12 x sin(30)
= 12 x (30/10 + 0.2)
= 12 x 0.5
X-wind component = 6 knots


I hope that makes sense.

Cheers

[RYR-738-JOCKEY]

Willit Run: I fully understand where you're coming from, but the one thing you forget is: If you don't obey you're company SOP, ie x-wind limit, you will be straight in for tea without biscuits if something happens. The limits is, as you say, test limits and you may or may not be able to land in excess of them.

[autothrottle]

Seem to remeber this from an SFC instructor in the early nineties. It is for approximate , quick guide to x-wind component.

Landing runway 27 , surface wind 300/20....wind 30 degrees off nose then take the next two figures down from 3( from the 30 degree bit) , ie 2 and 1. 1/2 OF 20 KNOTS EQUALS 10KTS X-wind comp.

Again landing runway 27, surface wind 320/30 , this time 50 degrees off nose then , 5, 4,3. 3/4 of 30 equals approx 22.5 knots or 22 knots for rough estimate.

Obviously only a rough rule but quite quick to establish if within limits!

Hope this is useful.:8

[Wilton Shagpile]

BTW, track miles to run......when you're on an intercept heading, for every 10 degrees that your track to the airfield differs from the inbound QFU, add 1 mile to the straight line DME distance.

WS

[spitfires rule]

A very easy method that I know is called the 60/60 rule.
Degrees of the runway x windspeed /60.
Works great but if the x-wind is more the 60 degress of the runway just use the windspeed as the x-wind component.

[Mark1234]

Use the old whizz wheel? Quick, easy and no maths required.

What's all this sinus stuff anyhoo? I thought they were somewhere up your nose, and it's the sine of an angle - I've never heard of a sinus in the context of maths.. could have missed something mind you.

[skiesfull]

Sine derives from Latin 'sinus' - curve, so put that up your nose!
Unless you have a cockpit readout that gives you exact crosswind, how will your management prove otherwise? Your company limits are more conservative than the manufacturers demonstrated limits. Use your calculation as a guide only; in strong crosswinds the strength will fluctuate anyway.

[alf5071h]

skiesful, Re “Your company limits are more conservative than the manufacturers demonstrated limits”. Your statement might be assuming too much; just as individuals lack accurate guidance on wind measurement, so do many operators on how to apply demonstrated limits – what do they (certification regulation, manufacturer, management, and the demonstrated value) actually mean.

You appear to be the first to consider wind strength, whereas previous posts only considered direction.
It’s continually surprising how human thought focus on just one aspect of a question; crosswind component is a function of direction and strength.

Slide rule accuracy in determining wind direction is of little value where the accuracy of wind direction might only be +/- 5 deg, or even greater error due to averaging methods.
Similarly, wind strength might be in error by +/- 10 kts; and then there are gusts.

Simple rules of thumb are valuable aids for determining ‘ball-park’ values which contribute to the assessment and judgment of the conditions and crosschecking other estimates or ‘computed’ values (computers rarely assess or judge). There are many other aspects that should be considered in association with a crosswind, e.g. runway condition (dry / wet / icy), runway width, aircraft configuration (and MEL), availability of max reverse (tail engines), landing weight in proportion to the maximum allowed for the runway length (braking effectiveness in a crosswind).

Operations in crosswind require careful thought; wind direction, speed and gusts, the components both across and along the runway, and particularly any tailwind component.
Remember that the component along the runway may be factored (tailwind 150%) when calculating landing distance, the result includes a margin for error.
What margins for error are there in distances across the runway in crosswind operations?
Are these included in operators limits or are they left to the judgment of individual pilots?
What would be a suitable margin (with / without gusts); would this be a proportion of the crosswind component or something else?

[low n' slow]

Oldest trick in the book:
Just look at your compass rose, HSI, EHSI or what type of instrument you're flying the approach on. In most cases it has a inboundcourse coinciding to the relevant runway track set to it.

- Put a finger on the number relating to the reported wind.
- Trace a line parallell and perpendicular to the inboundcourse on the instrument.
- Note where the parallell line intersects the inbound course and where the perpendicular line intersects with the deviation dots.

It makes it very easy to see what percentage of the wind you have coming in from the side and the nose/tail component. Just multiply that with the windspeed and you're home free.

/LnS

[skiesfull]

ALF5071H
Thanks for the lecture on the theory of crosswinds. Do you know of any airline applying stronger crosswind limits than the manufacturers' suggested limits?
The original poster asked for a guide to calculate the crosswind while on final approach and the replies have given a rough way to do so. My post was to suggest that crosswind calculations be used as a 'ball-park figure' only. Perhaps you could say as to what stage on the approach would you go-around, if your 'ball-park figure' exceeds the company's maximum? In my experience the maximum crosswind limit was never without moderate, even severe turbulence and I have twice gone around because of that, rather than the actual wind strength itself. Your observation that a surprising number of pilots only concentrate on the wind strength, is probably because with that strength of wind, we are concentrating on completing the landing safely and have little capacity to consider the other factors that you have stated.

[hvogt]

If you can remember the sin values above then you are a better man than most.handflown

I'm certainly not better than anybody else. When it comes to mental calculus I always used to be far below average. However, the good thing about mental calculus is that it's easy to improve your own abilities. Every morning after breakfast I take five minutes to practice with a small programme (including crosswind, tailwind, turns, etc.). It helps.

[hvogt]

Someone gave me a PM, asking about calculating tailwind components. So here you are:

TAILWIND = WIND SPEED * COS (WIND ANGLE)


Of course the same formula applies to headwind.

[old,not bold]

I never could get the sins right....

The thread reminded me of a chart we all used to use in the really olden days before we had confusers......

Google got it in one when asked "crosswind component chart"

http://www.nifa.us/judgesmanual/apendixC.pdf

But I guess having a piece of paper in your flight bag is sooooo old-fashioned...back to the trigonometry, chaps and chappesses...

[Old Fella]

Geeze fellas, now I know why I was a professional F/E and a Private Pilot. Talk about make things complicated, except that is for the "Clock method". But it seems to me that the best rule to follow would be that if you have any doubts about whether or not it is safe to land in the prevailing conditions, go around and make another approach. It could be that the pilot's "limit" may be less than the published "limit". As for x-wind "limits", either demonstrated or company SOP, if it appears in the Limitations Section of the FM, then it is a limit.

[old,not bold]

I still think that the sheet of paper (link above) with a chart on it is easiest, quickest and most accurate.

But then what do I know...

[alf5071h]

skiesful, et al. Sorry, didn’t intend to lecture (# 19); a sharing of thoughts, an observation of how PPRruNe’s think, and a reminder not to rely on a single data source etc, etc.

“Do you know of any airline applying stronger crosswind limits than the manufacturers' suggested limits?” No.
Although I am familiar with several aircraft types, I don’t have access to operator’s manuals. I suspect that the lack of response to the question in this and other threads, suggest that where operators publish a limit, they use the demonstrated value without additional margin. Hence my concern about understanding what demonstrated means and the errors in wind measurement / reporting.
I agree with the ball-park approach. Where to discontinue the approach probably depends on how a limit is determined and stated by the operator.
A hard rule like JAR-OPS RVR minima in low visibility enables a specific position; a more flexible rule like a stabilised approach (more variables) uses several decision points, i.e. 1000ft, 500ft, threshold, and even touchdown. The latter rule might result in more errors as several parameters have to be assessed - more opportunities for judgement. Even so, flexible rules should still have a final hard limit.

The concept of operator crosswind ‘limits’ appear to be even more flexible still (perhaps due to certification terminology, weak operational knowledge, etc), whereas in reality a hard limit is required (accident / incident statistics).
Comparing manual landings with autoland, the latter has a hard limit applied before an approach. Autoland limits include a safety margin due to difficulties in determining the system’s performance in the conditions. This is not so much a technical issue, (the reliability and consistence can be assessed), but more the variability of the conditions and their effect on the aircraft / autoland system.
To me this is similar to the problems experienced by crews during manual landings; they might miscalculate the crosswind component, or misjudge the effect of gusts;- human fallibility.
So just as the certification process adds a margin for autoland, so too should the operational process for manual landings.

I would recommend a hard limit less than the demonstrated value, but greater than autoland (credit for the positive aspects of pilot judgement). The limit would depend on good knowledge and training to provide the essential skills of judging and flying in such conditions (airmanship, currency).

In my limit, if the manufacturer does not specify any demonstration of gusts, then either gusts are limiting or factored, e.g. wind + half the gust. An absolute gust value might not be as important as reminding crews to think about the consequences of the risks from gusts.
More generally a safety margin of 60% of any wind speed error, or a combination with direction error (and calculation) could be used. This probably results in a 5 kt reduction from the demonstrated value (ball-park figure).
When to apply it? Earlier rather than later. Although wind measurement is historic (up to two mins), which might encourage a later assessment, this would result in less time for a well considered judgment and greater pressure to continue the approach (plan continuation bias; ‘press-on-it is’ – the closer you get the more you continue). In difficult conditions, turbulence, gusts, etc, crews should avoid increasing workload at a late stage of the approach where greater attention must be allocated to the flying tasks, thus a late consideration of a limit has greater risk. I suggest that the decision is made at 1000ft; this a consistent point with any RVR limit (if applicable) and a stabilised approach (IMC). An earlier decision also provides opportunity to refocus on the missed approach procedure, thus avoiding the rush of manoeuvring due to last minute decisions.

A lengthy view originating from a short question, but that’s like most safety issues.

Refs: Crosswind Certification - How does it affect you? (www.nlr.nl/id~5114/lang~en.pdf)
Safety aspects of aircraft operations in crosswind. (www.nlr-atsi.com/downloads/NLR-TP-2001-217.pdf)

[Charly]

Clock Method!!! My favourite!:D

Simple, does the job.

[Oakape]

If I need a reasonably accurate figure, I use the back of my CR-5 circular computer. All sorts of good stuff on that thing, needs no batteries & it fits in a shirt pocket too!

[asuweb]

I always have a chart to hand, similar to the one posted above, which I can quickly read off the X-wind and Headwind/Tailwind components. Very useful.

[s61n]

Lets keep in mind that the original request specified that you where "ON FINAL APPROACH", which probably means that you have a few other priorities besides working out the crosswind.

I had a good look at that sine tables once and found a, in my opininon, very simple system that seems to work. It is accurate within 2.5%, which, given the somewhat inaccurate wind reporting system that we have to live with, it's accuracy may be regarded as well within any practical limits.

Lets have a brief look at the cine tables, (and then forget about them):

Sine 0 degress is: 0

10 : 0.173648
20 : 0. 34202
30 : 0.5
40 : 0.642788
50 : 0.766044
60 : 0.866025
70 : 0.939693
80 : 0.984808
90 : 1


From a practical point of view, these figures are very interesting and,-
quite useless.

You will agree
That for 20 degrees: 0.34202 is very close to 0.3333 which is = 1/3
That for 40 degrees: 0.642788 is very close to 0.66666 which is = 2/3
That for 50 degrees: 0.766044 is very close to 0.75 which is = 3/4
That for 60 degrees. 0.866025 is very close to 0.9, so maybe you could multiply your given main wind by.9 and just round DOWN, ( thats veeeery close, no?)

So our new, final and complete chart could rather be:



20: 1/3
30: 1/2
40. 2/3
50: 3/4
60: .9


And thats ALL.
All above 60 degrees would be 1, or full wind strength.
A crosswind of 10 degrees is IMO if little interest anywhere below 100kts.

If you just could keep in mind the figures: 1/3, 1/2, 2/3, 3/4, .9 and the fact that your "1/3" starts at 20 degrees, you should IMHO have a perfectly adequate personal crosswind calcualtion system.

NB! Keep in mind that we, as pilots, normally seem to constantly underestimate our crosswind component.

Its more than a bit touchy to do so, but if you were to ask your highly experienced friend and collegue: You are landing on runway 18, tower reports wind 230/30. What is you effective crosswind component?
You'll find that more often than not the answer would be, "somewhere around 12-13 knots".(!)
But of course you would know better.

Finally, I think that with a little bit of cooperation, an even simpler, better system for crosswind calculation may be found, but for now, I'd very much appreciate anyones opinion of the simple procedure suggested above.

Stay safe.

[Piltdown Man]

0.5, 0.7 & 0.9 for 30, 45 & 60 degrees (or 60, 45, 30 for headwind) angle between track and wind. It's close enough for government work (and short finals on a "nasty" night).

PM

[old,not bold]

With the exception of asuweb, no-one has acknowledged that the single piece of paper with a X-wind component chart on it is easiest, quickest and most accurate method.

I'm really puzzled by this.

What is it about complex (to one degree or another) mental arithmetic, or using a calculator, PDA, laptop or whatever, that makes it so much preferable to use that, rather than just to read the X-wind component off a chart?

It takes 4.5 seconds, including the time needed to pull it out of the chart pocket, and it's accurate. All you have to work out mentally, at a moment of higher stress than usual, is the angle of the wind to the runway heading. There is nothing to remember, except where you put the chart.

[helimutt]

glance down at the RNAV box, NAV 3, then see the wind, drift angle etc, no need for complex/simple arithmetic. ;)

As for sine tables etc, come on. Just guestimate it, it changes all the way down the approach anyway if thats where you're using it.



Is the wind just off the nose by about 20 degrees? ok, so use about 1/3 of wind speed. 45 degrees? use about 2/3 wind speed. then up to 90 degrees? use all of it.

[slip and turn]

onb, I am sure you are right about the piece of paper, but if you had a piece of paper to remind you of all you needed to know before lunch today, then your cockpit would soon look like my great grandma's parlor :p

I am kinda surprised that trigonometry and simple vector mechanics seems such a black art to so many 'pilots AND navigators' ..., but then I guess there's more than one way of skinning a cat or landing an aeroplane thesedays - well that's what my great granny says when she discusses it with me :}.

Anyway, I am sure there's a few reading the thread who are grateful for the revision lessons on rules of thumb :ok:

I am sure what we see in this thread shows that with some parts of the syllabus at least, the ATPL Theory multichoice questions in the exams don't quite test understanding as rigorously as might be preferable.

We all know our angles at least. Personally I've then taught my kids to work out sine's, cosines and tangents from geometric first principles (right angle triangles - measure and calculate opposite/hypotenuse etc.) and plot them on a graph to get a better feel for it all - plot their own sine curve, get to know the shape of it, how the gradient reduces rapidly for those angles over 60 - they now associate the values with something they understand and can visualise in their mind's eye, rather than risk regurgitating poorly learned number lists incorrectly e.g. is it sine or cosine I need? Is sin60 .866 or is cos60 .5 ?? Is it sin or cos that is 0 at 0? And why's tan45 1?

Hopefully if they ever take to the air, and one day find themselves trying to make sense out of their Breitling watchface bezel and crosswinds, they'll soon sort themselves out :8.

[hugh flung_dung]

Why make something complicated when it can be staggeringly simple - no sums are needed.

When on final look at your DI/HSI and find the reported wind direction round the outside of it.
Mentally drop a line from the wind direction until it hits the horizontal centre line.
The proportion of the centre line between this intersection and the centre is the proportion of the reported wind that's across the runway.

(As originally described a bit earlier by low n' slow)

If you do the same thing horizontally you get the headwind.

This is as accurate as you want to make it and takes about 2 seconds.

HFD

(BTW, if you want to know what the components are before you reach final just turn another compass rose (RBI/CDI?) to the runway track and use that)

[mini-jumbo]

Why make something complicated when it can be staggeringly simple - no sums are needed.Erm, your method still requires a calculation, because effectively all you are doing is finding the number of degrees off runway heading. You still need to apply that figure (whether calculated or using your HSI method) to the reported wind speed to get the x-wind.

Personally, I'm with the piece of paper. Where I fly, we are load limited, and evey knot of wind makes a large difference, hence a piece of paper with both headwind and crosswind component.

[hugh flung_dung]

mini-jumbo:
IME people find it easy to judge ratios/proportions but impossible to do "proper" sums. In fact I can't remember more than a handful of (admittedly, private) pilots over the years who've managed to give me more than a random number when I've asked them for the crosswind component.

(FWIW the same method can be used for drift and gs calcs if you know MaxDrift)

HFD

[er340790]

When you're on short final and have about 10 seconds when the tower gives you the wind direction/speed, the best rule of thumb was:

For each 10 degrees of X-wind take one sixth (1/6) of the crosswind value.

eg landing on runway 04 with x-wind of 12 kts from 060

Wind = 20 degrees from right so 2/6 or 1/3 of 12 = 4 knots x-wind.

With a bit of practice you can do any permutation in your head in well under 5 seconds!!!

[mini-jumbo]

HFD, fair point. I guess for some people visualisation, ratios etc works better.

[mini-jumbo]

er340790, I don't mean to be pedantic, but in the interest of clarification, I assume you mean when TWR gives you the w/v, you then use your method to calculate the crosswind?

[sayagaingoaround]

Here's one i don't think has been mentioned: i'm ready to be slated by the mathmeticians!!

For Crosswind component ..... Wind Angle + 20 in % = XWC

ie Rwy 26 Wind 300/30 (40+20) = 60% = 18kts

For Headwind Component ...... 110 - Wind Angle in %

ie Rwy 26 Wind 300/30 (110-40) = 70% = 21kts


Seems to work fairly accurately, I also like the clock method and of course the good old graph, especially when winds get a bit close to the limits!

[finncapt]

On approach, are you interested in the x-wind or the wind vector which gives you the maximum allowable/demonstrated x-wind for the runway in use?

When on Budgies in the Scottish Isles (and DC10 at bermuda), I used to write a wind table, for each ten degrees, giving this wind vector. That way I knew if I was within the limit.

It was sometimes useful to tell (ask) the controller to give no further wind checks after receiving one within limits.
A wind above the demonstrated limit was acceptable if everything felt right, whereas on other occasions I have gone around when the x-wind was within limits because turbulence made the aircraft almost uncontrollable.

A particular problem with a strong x-wind at 90 (or there about) degrees to the runway can be the along runway component.

Sumburgh 09/27 (15/33 not available at night) is a case in point.

A small change in wind direction can, with a strong northerly, cause the wind to come around the other side of Fitful Head giving an unexpected and sudden tailwind on landing despite the reported wind appearing to be a headwind
There is not much tarmac left if you land (three reds and a white and little or no flare - my technique at Sumburgh at night) with an 18kt tailwind on 09 !!
Cost me several beers to the firecrew in the helicopter club that night!!

[link_142]

sayagaingoaround,

thats the method i always use....its a rough rule but works fine for me! :ok:

[flyr767]

You can find both the headwind or tailwind and the crosswind with this formula (a TI-83 calculator will do well with this):

sin(wind_direction-current_heading)*wind_speed = headwind or tailwind component

cos(wind_direction-current_heading)*wind_speed = crosswind

For headwinds and tailwinds, a negative number means a tailwind and naturally a positive number is a headwind.

For crosswinds, a negative number is from the left. A positive number means winds are from the right. Hope this helps!