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Old 28th Mar 2008, 15:18   #1 (permalink)
 
Join Date: Apr 2005
Location: UK
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Question Working out the crosswind component

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
Cactus99 is offline  
Old 28th Mar 2008, 15:23   #2 (permalink)
 
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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......

Last edited by wiggy; 28th Mar 2008 at 15:55.
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Old 28th Mar 2008, 15:28   #3 (permalink)
 
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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.

Last edited by hvogt; 10th Jun 2010 at 15:34.
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Old 28th Mar 2008, 15:51   #4 (permalink)
 
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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).
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Old 28th Mar 2008, 15:52   #5 (permalink)
 
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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
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Old 28th Mar 2008, 18:00   #6 (permalink)
 
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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.
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Old 28th Mar 2008, 18:22   #7 (permalink)
 
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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
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Old 28th Mar 2008, 20:18   #8 (permalink)
 
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Very helpful, thanks for all the replies chaps, big help!!
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Old 28th Mar 2008, 20:40   #9 (permalink)
 
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Always wondered why don't say "cleared to land, cross wind component xxkts" instead of "cleared to land, surface wind xxx/xxkts"?
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Old 28th Mar 2008, 21:10   #10 (permalink)
 
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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?
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Old 29th Mar 2008, 00:58   #11 (permalink)
 
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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.
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Old 29th Mar 2008, 12:02   #12 (permalink)
 
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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
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Old 29th Mar 2008, 18:46   #13 (permalink)
 
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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.
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Old 29th Mar 2008, 20:00   #14 (permalink)
 
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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.
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Old 29th Mar 2008, 21:21   #15 (permalink)
 
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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
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Old 30th Mar 2008, 03:31   #16 (permalink)
 
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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.
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Old 30th Mar 2008, 12:41   #17 (permalink)
 
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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.
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Old 30th Mar 2008, 13:14   #18 (permalink)
 
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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.
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Old 30th Mar 2008, 18:12   #19 (permalink)
 
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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?
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Old 30th Mar 2008, 19:13   #20 (permalink)
 
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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
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