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Thread: MSA question

  1. #1
    Join Date
    Jun 2006
    Location
    Milford, Ma, USA.
    Posts
    107

    Default MSA question

    I'm on a flight to NZWN New Zealand landing RW 34 ILS via Umaga. I normally fly using approach charts but don't turn on ATC. The way I read the chart I should arrive at UMAGA at 2000 ft. However the MSA for that heading says I should be at 4800. Every time I pay attention to MSA I come in way too high. Am I interpreting the chart wrong ? How should MSA be used when I'm looking at approach plates.

  2. #2
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    6,519

    Default

    Minimum Sector Altitude is listed for a certain distance from the field (often 25 NM), and is an altitude guaranteed to give you safe clearance above ALL terrain and obstacles in that sector. The approach path often has you at lower altitudes in most areas, and those are defined on the plate. Initial and final approach fixes, DME arc altitudes, and many other things on the plate give you more appropriate altitudes.

    If you look at the NZWN (Wellington) ILS/DME approach plate you'll see all kinds of obstruction altitudes and DME arc altitudes and holding pattern altitude, etc., all of which give you clues where you should be, but the profile view (below the plan view) shows what altitudes you should be at when reaching various fixes, and that's what you should follow once on your final approach path, starting with 3,980 feet at WITBY, descending to cross FAP at 3,000, CANES at 2,630 feet, etc. Note that DME distances are given from IEB (not the Wellington VOR/DME). and those distances define the various fixes, which is why DME is required for the approach.

    There is much more information on the plate, but that should get you started.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  3. #3
    Join Date
    Jun 2006
    Location
    Milford, Ma, USA.
    Posts
    107

    Default

    Thanks for the info. There is so much data on these charts it can be a bit much to sift through it all, but I get the point. Sometimes I wish ATIS would give data on the runway in use a little earlier so I would have a little more time to plan my approach. Although I don't use ATC much I do tune ATIS to see where the AI traffic will be.

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