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## Crosswind

• Lancemosen
• Topic Author

### Lancemosen created the topic: Crosswind

Hi. Can work it out. On page 321 in the rpl study guide. Crosswind component. Runway 06. 110M at 30 knots. For crosswind component locate 50 How do you get the 50 Cheers Lance

• Mister W

### Mister W replied the topic: Crosswind

Hi Lance,
When working out the crosswind component, you are looking for the difference in degrees between the runway direction and the wind direction. In the question you have described, the runway direction 06 or 060°M and wind is coming from 110°M. Giving you 50° from the right difference. That's where the 50 comes from.

Little tip for working out if the wind coming fom the left or right. Number of the wind direction is bigger than your heading. The wind is coming from the right. Number of the wind direction smaller than your heading. The wind is coming from the left.
Example: RWY 18 Wind 210° at 30 normally written as 210/30 equals 30° crosswind from the right. RWY 09 wind 040/20 equals 50° crosswind from the left.

Hopes this helps

Mister W.

• Posts: 20

### Chao replied the topic: Crosswind

Hi Mister W,

Recently, I am reading the same book, having another question.

As you said, same as in the book too, Number of the wind direction is bigger than your heading. The wind is coming from the right. Number of the wind direction smaller than your heading. The wind is coming from the left.

Is this for all conditions? Example: RWY04/22, Wind350°at 30kt. So use runway is 04, wind from left. is it right? Number of the wind direction is bigger than heading, but the wind is coming from left. Am i right or i miss something?

Thanks

Chao

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 391

### John.Heddles replied the topic: Crosswind

If you choose to use this larger than/less than approach, then if north figures in the sums, you need to keep increasing rather than going back to 000. This will avoid the problem you have cited.

So, for instance, with your example -

RWY04/22, Wind350°at 30kt. So use runway is 04, wind from left. is it right? Number of the wind direction is bigger than heading, but the wind is coming from left. Am i right or i miss something?

For the purpose of the sum, make the runway direction = 360 + 040 = 400 (which is the same as 040 using the conventional 360 degree clock face).

Now, when you run the sum, you get 400 - 350 = 50 degrees from the left.

Generally, this approach is fine when you are in the early learning stages. However, once you get past that, you MAY find it easier to visualise the compass rose and figure it that way. So, in this case the runway is 040, ie 40 degrees off to the right of north, while the wind is from 350 ie 10 degrees off to the left of north. A simple addition and you have 40 + 10 = 50 with the wind from the left. Easy peasy.

In fact, I suspect that you did this first up .. how did you establish that you would use runway 04 rather than 22 ?

Engineering specialist in aircraft performance and weight control.

• Posts: 20

### Chao replied the topic: Crosswind

Hi John,

Thanks your explaination. Yep, I am still in early learning stage. For how I came up with question, just like ' what if'. As to using runway 04 rathan than 22, it's because 04 is close to 350, combining cross-wind and head. Is that right?

Thanks,

Chao

• Posts: 61

### HPOUND replied the topic: Crosswind

I think of winds and runways like this:

METHOD 1: Maximise the headwind, minimise the cross-wind. So if the the wind is coming from X degrees, the runway to use will be greater than X-90 and less than X+90 (all divided by 10). Example: Wind is 350/15 (15kt coming from 350). So the runway we prefer in order for the prevailing wind to offer a headwind on t/off or landing will be any runway 26 through to 08. If there are two or more runways within this range, pick the one closest to the wind. This will be the runway with the smallest difference b/w the wind direction (divided by 10) and the runway heading. Using your numbers, you'll see that runway 04 falls within our range (26 through 08) while 22 does not.

METHOD 12: Find the runway that gives the smallest absolute difference b/w runway heading and wind. If wind is 350, runway 04 gives an absolute difference of 50 while runway 22 gives an absolute difference of 130.

In answer to your question, we don't "combine" headwind and crosswind. They're already combined in "the wind", wherever it comes from. However we can disaggregate the wind into two components - one component coming from directly in front (the headwind), and the other coming from directly abeam (the crosswind). "It's because 04 [runway]is close(r) to 350 [wind]"... absolutely correct!

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 391

### John.Heddles replied the topic: Crosswind

As to using runway 04 rathan than 22, it's because 04 is close to 350, combining cross-wind and head. Is that right?

Chao, Looks like you are three-quarters the way to doing this stuff via visualisation rather than sums ... well done.

I think of winds and runways like this:

Not always that simple, unfortunately. When you get out into the real world you may find that other considerations dictate runway selection. Main thing, in the question context, is to observe crosswind and tailwind limitations.

Engineering specialist in aircraft performance and weight control.

• Posts: 61

### HPOUND replied the topic: Crosswind

John.Heddles wrote: Not always that simple, unfortunately. When you get out into the real world you may find...

That's a very condescending reply. What "world" are you assuming I am in? We're all here either looking for help or helping others, so let's keep it positive!

In the context of the original question, actually it is that simple. Sure runway surface/length/slope, density altitude, wet/dry are vital considerations when determining preferred runway, but they are unnecessary complications given the original post.

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 391

### John.Heddles replied the topic: Crosswind

My apologies if you found the reply to be so. It was not so intended.

What "world" are you assuming I am in?

I have nil knowledge of your background and the aviation world in which you may have experience. I am referring to the real world out there in commercial aviation land. When it comes to airline and charter operations runway selection is not predicated just on headwind (while noting that crosswind limits must be observed). Tailwind takeoffs are not at all uncommon and may be selected for reasons of commercial expediency, runway parameters such as slope, obstacle profiles and escape path complexity, and so forth.

We're all here either looking for help or helping others, so let's keep it positive!

I would have thought I was doing precisely that ?

In the context of the original question, actually it is that simple.

Then we shall have to agree to disagree, I guess.

.., but they are unnecessary complications given the original post.

Perhaps a simple question might be answered in a simplistic manner. However, the main benefit of this sort of website is that the new student folk can benefit from observations by those who have significantly more experience and technical background. To deny the upcoming student that benefit, in my view, would be a tad silly.

Engineering specialist in aircraft performance and weight control.

• Posts: 61