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## Performance- ETP question

• Topic Author

### Huskyblade created the topic: Performance- ETP question

Hi all,

Wondering if somebody could shed some light on this type of question for me, would be hugey appreciated if you could show me were Im going wrong.

When calculating the following ETP with information;
TRACK - 268*M / 335nm
TAS - 380kts
WIND - 230*M/40

If the forecast wind was wrong and the actual wind was 200*M/60, how much would the ETP move and in which direction?

• Posts: 7

### MaxCavill replied the topic: Performance- ETP question

Hey Husky!

As you might know ETP's are a distance from a specific point, as where PNR's are a time from a specific point. So for this question our calculation will give us a distance from X.

First thing you should do is have the equation written down so it's easy to follow along, and almost removes all mistakes.

Total Distance x Groundspeed Home
TAS X 2

1. Figure out the distance, easy because the questions states the total distance between the points. Some questions you will have to figure out the distance by the groundspeed and the time flown. -

So distance = 335 nautical miles.

2. Get your GS home (home being "Starting Point"). So TAS +/- the the condition of wind. (HW/TW) - so calculate head/tailwind component . ~32 knots of headwind on the way out = ~32 knots of tailwind on the way HOME.

Therefore groundspeed home = 380+32 = 412 knots.

3. Just multiply TAS by 2.

TAS x 2 = 380 x 2 = 760

Finally just plug the numbers in and you have the initial part of the question.

To do the 2nd part of the question, change the wind component for the equation. everything will remain the same.

tailwind component on the way home is now: ~7kts of tailwind home.

so....

335x387
760 = 171nm from point A.

What we can see is the ETP has moved FURTHER UPWIND, as it always will with the addition of wind. (Simple rule of thumb) by how much? 11nm! What direction? Towards departure aerodrome or EAST.

In short answer = 11nm moved towards the departure aerodrome/east.

If there are any more questions, feel free to ask
The following user(s) said Thank You: Huskyblade

• Topic Author

### Huskyblade replied the topic: Performance- ETP question

Thanks Max for the detailed response & taking the time. Was a great help.

• Topic Author

### Huskyblade replied the topic: Performance- ETP question

Hey Max,

Could you let me know how you got the wind component for B as I get a different figure;

268* Track - 200* Wind
= 68* Angle @ 60Kts
= 22.8Kt wind component.

I have attached my working in the attachment. Not sure what I’m doing wrong if its meant to be 7kt component after the conversion.

Thankyou

• Posts: 7

### MaxCavill replied the topic: Performance- ETP question

Yep- just did it on my flight computer and I got 22 knots tail also. Not sure how I got 7. But principle is the same, the working will be identical no matter the numbers.

• Topic Author

### Huskyblade replied the topic: Performance- ETP question

Thanks Max, really appreciate it.

Is there a way to calculate wind from the charts in ersa when you have an angle of more than 90 degrees.

For example Track of 165* & a wind direction of 260*/60

Thankyou again