# How to calculate W/V from true HDG/TRK/GS using a CRP-5 flight computer?

I am currently studying for my EASA ATPL (airline transport pilot license) and one of my subjects is General Navigation.

I have stumbled across this question (picture) that has completely stumped me, I have not been able to find help anywhere else. I know it can be solved by drawing wind triangles but I am solely interested in solving it using the CRP-5 flight computer.

I am very much used to calculating desired headings for a certain track when given wind, but not the other way around. Any help would be greatly appreciated.

• Answered here: – mins Jan 18 '17 at 10:22
• @mins thanks for the solution, I was looking more for an explanation as to WHY it is done that way so that I can be prepared for any variation, although your response did help me a lot! – gaveasky Jan 18 '17 at 10:48
• Hi and welcome to Aviation SE. If that's the intent of your question, then please edit it to make it clearer. At it's simplest, you are just solving a triangle of velocities. Given two, find the other one. – Simon Jan 18 '17 at 11:15
• CMC's answer seems quite complete, with explanations. Explain in your question which part you feel is not logical. – mins Jan 18 '17 at 13:02

To work this problem in reverse:

1. Set the True Course (Track) at the Index and slide the grommet over the Ground Speed (GS) of 242 knots:

1. Draw a dot with an arrow behind it, marking the wind vector at the intersection of:

a) 8° right of center because the wind correction angle or heading is right of course (74° TH minus 66° TC); and

b) 230 True Airspeed (TAS)

Now, above, you are able to visualize the flight. You could even draw your airplane in the middle and see the wind is a right quartering tailwind.

1. Finally, rotate the wind to the Index to read the answer. Slide the center grommet over any line that's easy to read. Read the wind speed up from the grommet (35 knots) and wind direction (from 180°) at the index:

• Ironic: after well over a decade of airline flying (this being a question for an ATP test), I'd be in desperate need of a refresher course on these tools in order to be able to solve this problem. Heck, I don't think I ever did anything like this in the Air Force after leaving pilot training. I'll grant that it's good to know the theory behind what the FMS and flight planning software is doing, but as far as a practical skill to have, this stuff isn't on the list. Not even close. – Ralph J Jun 17 '17 at 3:00