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4 Answers

IFR flight plan – convert winds aloft true to magnetic

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For IFR flight planning I've learned from King ground school videos the following:

  • Identify course on IFR chart (this is magentic)
  • Find winds aloft at your altitude (this is true)
  • Convert wind to magnetic using magnetic variation on chart
    • true wind = 360
    • variation = 15 E (east is least, west is best)
    • magnetic wind = 360 - 15 = 345

In doing a mock oral for my IFR check ride the other day, my CFII said that I'm wrong in subtracting the wind (using the above scenario).  This is VERY confusing.  I watched the King IFR flight planning video again and that's how John King says it's done.  I know he's not the "end all, say all" but he's pretty darn experienced so I decided to get your opinions on whose right.  My CFII or John King?

I need to figure this out so I don't screw up my flight plan on my check ride in 10 days.


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4 Answers

  1. R. Anderson on May 06, 2017

    Seems pretty simple (King’s explanation), so I wonder what your instructor’s point of view is. Winds Aloft (FB) are in reference to True North. So, if your actual position is at a location where the magnetic variation is 15 degrees East then the magnetic wind direction would be, in your example, 345 degrees (360-15 = 345).

    Perhaps it’s just a communication confusion between you and your instructor. So why don’t you go back to him and discuss the guidance shown in the Advisory Circular entitled Aviation Weather Services, AC -0045G, paragraph 7.4.

    You will do better in your check ride if you have confidence that you’ve sorted this out.

    Good luck

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  2. sp_72 on May 06, 2017

    Thanks for the clarification!

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  3. Russ Roslewski on May 06, 2017

    In VFR flight planning, you traditionally figured a true course, then used true wind to figure a wind correction angle, therefore a true heading, and finally a magnetic heading. So the conversion to magnetic was done at the end.

    In IFR flight planning, you have magnetic course already. So you need to do one of the following things:
    – convert the wind to magnetic first, as you are doing, or
    – convert the course to true before applying the wind.

    Either way will ultimately work, your instructor may have just learned the opposite technique.

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  4. Mark Kolber on May 07, 2017

    Russ makes an important point. There are two ways to do the calculation. sp_72, have you compared the King and your CFI’s answer to the same question? If they are the same, the method makes no ulrimate difference (although I personally think the King method makes more sense for IFR).

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