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5 Answers

Maximum Elevation Figures

Asked by: 29193 views
General Aviation

Are the maximum elevation figures (MEF) on sectional charts rounded up to a certain value (If so, by how much)?

I am having difficulty finding an obstacle in the quadrangle with the elevation of the displayed MEF.  I have found obstacles close to the MEF value, but never the exact value.

While the sectional chart explains what maximum elevation figure is, it doesn't mention any degree of rounding.

 

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5 Answers



  1. Steve Pomroy on Feb 25, 2011

    Hi Flight Student.
     
    On Canadian charts, the MEF is the highest obstacle in the quadrant plus either:
     
      a) 328 feet if the highest obstacle is terrain or natural, or
      b) nothing of the highest obstacle is manmade,
     
    and then rounded up to the next 100′ interval.  328 feet seems like an odd number, but it’s based on the fact that the initial obstascle clearance is determined in meters (328 feet = 100 meters) and then converted.  Why this particular number starts in metric while all the other numbers are in feet or miles to begin with has always struck me as odd.  but it’s probably to allow for obstacles lower than 100m are not portrayed on the chart (although this is not actually stated anywhere in documentation that I’ve found, but it would be similar reasoning to the determination of MEF on US charts — in other words, it’s an educated guess).
     
    According to the folks at AOPA, MEF on US sectionals is determined a bit differently (the main difference being the use of 200 feet rather than 328 feet, so it’s still essentially the same concept – highest terrain/obstacle plus a small fudge factor):
     
    http://flighttraining.aopa.org/students/crosscountry/special/Intro_to_VFR_Chart_Symbols.pdf
    —BEGIN QUOTE—
    The Maximum Elevation Figure (MEF) represents the highest elevation, including terrain and other vertical obstacles (towers, trees, etc.), within a quadrant.  A quadrant on Sectionals is the area bounded by ticked lines dividing each 30 minutes of latitude and each 30 minutes of longitude. MEF figures are depicted to the nearest 100′ value. The last two digits of the number are not shown. In this example the MEF represents 12,500′. MEFs are shown over land masses as well as over open water areas containing man-made obstacles such as oil rigs.
     
    In the determination of MEFs, extreme care is exercised to calculate the values based on the existing elevation data shown on source material. Cartographers use the following procedure to calculate MEFs:
     
    When a man-made obstacle is more than 200′ above the highest terrain within the quadrant: 1. Determine the elevation of the top of the obstacle above MSL. 2. Add the possible vertical error of the source material to the above figure (100′ or 1/2 contour interval when interval on source exceeds 200′. U.S. Geological Survey Quadrangle Maps with contour intervals as small as 10′ are normally used). 3. Round the resultant figure up to the next higher hundred foot level. Example: Elevation of obstacle top (MSL) = 2424 Possible vertical error + 100 equals 2524 Raise to the following 100 foot level 2600 Maximum Elevation Figure [2600 (portrayed as 2^6)]
     
    When a natural terrain feature or natural vertical obstacle (e.g. a tree) is the highest feature within the quadrangle.: 1. Determine the elevation of the feature. 2. Add the possible vertical error of the source to the above figure (100′ or 1/2 the contour interval when interval on source exceeds 200′). 3. Add a 200′ allowance for natural or manmade obstacles which are not portrayed because they are below the minimum height at which the chart specifications require their portrayal. 4. Round the figure up to the next higher hundred foot level.
    —END QUOTE—
     
    Cheers,
    Steve
    http://www.flightwriter.com

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  2. Wes Beard on Feb 25, 2011

    Steve is correct!  The MEF is calculated by taking the highest obstacle and adding a certain value to it.  If the highest obstacle is God-Made then we add 200 feet and round up and if it is man-made we add 100 feet and round up.
     
    I only comment to add the reference to find this information.  Aeronautical Chart Users Guide v9 page 2 (Click on Intro to VFR Symbols)

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  3. Matthew Waugh on Mar 05, 2011

    But think how much more exciting flying would be if they rounded DOWN……

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  4. Anastasia on Nov 13, 2013

    Jeppesen manual says it rounded to the next 100 foot level and 100 to 300 feet added to that figure depending on nature of the terrain

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  5. Anthony Dawson on Dec 28, 2017

    Must be an upper limit to the ‘1/2 the contour’ part as well. Look at the quadrant around this airport on the PHX Sectional. San Carlos Apache. (P13)

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