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HOW TO DETERMINE CRUISE ALTITUDES

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FAA Regulations, General Aviation, Private Pilot, Student Pilot

I watched an oral on youtube that seemed pretty comprehensive. They said that you base altitude selection on Magnetic Course. The way Magnetic Course was explained to be determined was True Course +/- Variation. He explicitly asked "What if you were going to fly the V176 (176 derees magnetic) airway, and determined your altitude to be 7,500 (based on Manetic Course), and winds from the right caused a 10 degree correction, now you're Compass Heading you're flying (assuming +/- 0 deviation) is 186, wouldn't you have to change your altitude to Even thousands plus 500?" and the answer was (according to this examiner) No, you would select altitude off of Mag. Course. All the Jeppesen Products(knee board, E6B) show TC +/- WCA= TH; TH +/- VAR=MH; MH +/- DEV= CH. The ASA products show TC +/- VAR=MC; MC +/- WCA=MH; MH +/- DEV=CH

The youtube Exam (which was 1.5 hours long, so I noted the time to fwd to so you can see what I'm talking about

 http://www.youtube.com/watch?v=kr483zBbQKw&feature=related    1:09:39

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1 Answers



  1. Wes Beard on Oct 30, 2012

    The examiner is correct. In that example, you would stay at your altitude of 7,500. The regulation §91.159 for VFR and §91.179 for IFR explicitly states magnetic course.

    To convert from true to magnetic and vice versa you would add the variation. East is least and west is best is the saying. If you are adding an easterly variation you would subtract and a westerly variation you would add.

    Your confusion is coming in the calculation from a magnetic course to a magnetic heading. Since the regulation doesn’t care what heading the nose is pointed towards just its ground path, so to speak… that calculation does not factor into the cruise altitude selection.

    As an aside worth mentioning. Both the Jeppesen and ASA formulas are correct. I prefer the Jeppesen method TC +/- WCA= TH; TH +/- VAR=MH; MH +/- DEV= CH due to the fact that the winds we receive on the weather report are reported in TRUE and not magnetic. If we follow the Jeppesen method, we will get a more accurate wind correction angle. Using the ASA method, we would need to first convert the TRUE winds to magnetic winds for the same accuracy.

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