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Magnetic Compass Dip Erros

Asked by: 739 views Aircraft Systems

For the magnetic compass, I understand the theory behind dip error and the famous UNOS, what I'm a little confused over is in which headings does it lag and lead. The reason I ask is because the FAA publications (Instrument flying handbook pg. 5-13, PHAK pg. 8-26) say it leads in the north and lags in the south, while everywhere else says the opposite, it leads going through sough and lags in the north. What am I missing here? 

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2 Answers

  1. Best Answer

    Russ Roslewski on Aug 01, 2017

    Wow. yes, the FAA publication is incorrect. It does appear that the two documents are literally a cut-and-paste of each other, so one was typed in incorrectly and the other as a result matches it.

    While the paragraphs explain the reasoning backwards, they do get the actions correct. In a northerly turn, roll out before you get to the desired heading (Undershoot it, because it Lags). Vice versa in a southerly turn.

    It’s really easy to see this effect in flight. A few minutes of visual turns somewhere with nice north/south roads will make it immediately clear what is happening, regardless of erroneous descriptions of why.

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  2. KDS on Aug 05, 2017

    I won’t weigh in on this topic, but I recommend that you follow the guidance in the publication where it says:

    Comments regarding this publication should be sent, in email form, to the following address: AFS630comments@faa.gov

    Then, let us know what they tell you.

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