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    3 Navaid Visual Fix WAS : Compass Error Correction
    From: Antoine Couëtte
    Date: 2010 Apr 21, 00:59 -0700

    Dear "M. Byronink",

    In reference to [NavList 12879] Re: Compass Error Corecction
    From: byronink---com
    Date: 20 Apr 2010 17:32

    You indicated :

    QUOTE

    " The third would not be part of the fix, but an indicator of accuracy."

    UNQUOTE

    Very good point ! I fully agree to your innovative view-point then.

    Let us use the 2 closest Navaids Intersection ("decent" cut angle required still), AS LONG AS the third (and farthest) Navaid indication is CONSISTENT with such Intersection. If any discrepancy, INVESTIGATE ... and just do not take the 2 closest Navaids LOP's at face value ... You might just simply have mis-identified one of these supposedly closest Navaids - or even both - either on land or from the chart.

    "Tradition" has been to use 3 Navaids instead of (only) 2 simply because from 3 Navaids you can derive 3 different 2 LOP fixes, and as consequence the possibility/probability of a 3 independent LOP derived fix being "too far away" for true position has been very greatly reduced. The existence of a "triangle / cocked hat" ensures some kind of "reliability / safety" (rather than "accuracy" as you earlier indicated) in the sense that "we should (certainly) be somewhere close from its center" while the intersection of the 2 closest Navaids ensures some kind of "Best Available" Accuracy.

    It would certainly not be good headwork to simply discard any information derived from the farthest Navaid independent LOP information. I would expect any Skipper / Commanding Officer not to accept it, unless his Navigator would present him with some kind of a third independent LOP, from the depth measuring equipment or from the Radar for example, or unless only and no more than 2 LOP's are available.

    As a Conclusion, and as long as there is some kind of a third independent LOP available to confirm that it is very reasonable to use only the 2 closest Navaids LOP's Intersection, then your view point is Excellent : Derive your "Best Available Accuracy" FIX just from the 2 closest Navaids LOP's Intersection.


    Congratulations to you and Thank You for sharing this very instructive view-point to cover this subject.

    My guess is that it will sooner or later become taught in all Navies around the world ! So, it is GREAT !

    Best Regards to you and to our NavList Community

    Antoine M. "Kermit" Couëtte


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