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## Landing / take-off charts and wind

• Posts: 7

### jaser33 created the topic: Landing / take-off charts and wind

Howdy aviators!

I'm trying to work out where I might be going wrong when it comes to P charts.
The main issue I have here is wind direction.

Here's an example:

Runway 06/24
Ambient wind = 020M/20 KT

Using the wind component chart, I calculate a headwind of 15kts, and a crosswind of 13kts using RWY24.

This would obviously give 2 different calculations on the chart. My question is, do I use the headwind or crosswind component?
Is there an angle where it switches to one or the other, or do I just use headwind regardless? I'm reasonably sure I don't just use the supplied wind of 20kts.

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 833

### John.Heddles replied the topic: Landing / take-off charts and wind

This would obviously give 2 different calculations on the chart. My question is, do I use the headwind or crosswind component?

One never runs P chart calcs with a crosswind component. You do, however, check that the crosswind doesn't exceed your aircraft limits for crosswind. You only use the head or tail wind component for the chart calcs. The only time you use the wind as presented is if it is straight up or down the runway, ie a straight head or tail wind.

If you are still not sure, why don't you post an example or two of your solutions for comment ?

Engineering specialist in aircraft performance and weight control.
The following user(s) said Thank You: jaser33

• Posts: 7

### jaser33 replied the topic: Landing / take-off charts and wind

Thanks for the speedy reply John. That has clarified.
I will post a couple of examples though just to make sure I'm on the right track.

Example 1:
Runway 06/24
Pressure height = 4000 FT
Temperature +20C
Surface = Short wet grass
Slope = Level
Ambient wind = 020M/20 KT
Take-off distance available 900 metres

I calculate headwind to be 15kts.
Crosswind is 13kts which is within limits.

For this calculation, I have come up with 940kgs.

Example 2:
Runways 08/26
Pressure height 5000 feet
Temp = +20C
Take-off Distance Available 800 metres
Surface = Short wet grass
Slope = 2% Down to the W
TAF wind = 230/20
Variation 10E

I calculate headwind to be 17kts, however there is a Variation of 10 kts from the East.
East is least, so take 10kts off before the wind component calculation, making the head wind 8kts. (hoping I have this right)
Crosswind is 5kts which is within limits.

For this calculation, I have come up with 965kgs.
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• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 833

### John.Heddles replied the topic: Landing / take-off charts and wind

I'll have a look at the working later today when I am near a printer so that I can play with the graphics more easily.

However, there is one major problem in your comments. Any reference to "variation" with a bearing designator (such as "E" or "W") relates to bearings and directions, NEVER speeds. Perhaps you can rework that chart without the wind component adjustment ?

Engineering specialist in aircraft performance and weight control.

• Posts: 7

### jaser33 replied the topic: Landing / take-off charts and wind

Taking into account the wind, I got my calculation wrong anyway.
I have had another crack at it (example 2)

The headwind component is 18, which is what I was supposed to have calculated the first time.
You are correct, I definitely took the 10 off the wind speed and not the heading. Thanks for pointing that out!

My new calculation is 1030kg.

Feel free to throw some difficult ones at me. The more I know these, the better!

• Posts: 7

### jaser33 replied the topic: Landing / take-off charts and wind

Hey John. Did you get a chance to look at this?

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 833

### John.Heddles replied the topic: Landing / take-off charts and wind

Having a look, now.