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Why MAP and the starting point of the segmented line do not coincide?

Asked by: 483 views General Aviation

Have a look at this chart: http://155.178.201.160/d-tpp/1701/09491R16.PDF (KEKS RNAV(GPS) RWY 16)

In the profile view of this chart, why the MAP (RW16) and the starting point of the segmented line signifying the missed approach course do not coincide? Not just in this chart. As I see it, it looks like there are a greater number of charts with this disagreement than those with coinciding the MAP and the starting point of the segmented line. How am I supposed to interpret this?

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1 Answers

  1. Best Answer


    Russ Roslewski on Jan 20, 2017

    Understand that what you are looking at on this approach (like many, many others) is actually 4 approaches combined into one chart. They are all identical up to the final approach fix, but the DA/MDA is different for each of the four. Then once passing the MAP, the missed is back to being the same for all of them.

    Each line of minimums is really a separate approach:
    LPV
    LNAV/VNAV
    LNAV
    Circling

    What is the MAP on a vertically guided approach? It is defined as the point where you reach DA on the design glidepath. This will happen at some point before the runway, and on this approach will happen at different distances from the runway depending on if you are flying the LPV or LNAV/VNAV line of minima. So the notional depiction of where the dashed “missed approach” line starts is basically correct for these two lines.

    For the LNAV and Circling lines, the MAP is at the runway threshold, RW16. So the dashed line is NOT correctly depicted for these non-vertically guided lines.

    So, basically they chose to depict one and leave the other one off, presumably based on chart clutter. The charting standard says to depict the dashed line based on the “best” level of minimums, in this case the vertically-guided LPV line.

    If it instead depicted the line leveling off and going to the LNAV/Circling MAP (RW16), then you could just as readily ask the reverse question – “why does the solid line level off and go all the way to the runway, when I know I’ll be going missed before that, when I reach DA?”

    In reality, once flying, it doesn’t matter which is depicted, since you won’t be looking at the chart at that point anyway. You fly to the MAP (either DA or the fix) as appropriate, and go missed from there.

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