Big number and small number on chart
- Thread starter adamgreene1988
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add 2 zeros. i.e. "28" means 2800 feet MSL. I believe it is telling you the highest elevation of any obstacles, mountains, etc..
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These are called maximum elevation figures (MEF) shown in quadrangles bonded by ticked lat/long lines.
The MEF are represented in thousands and hundreds of feet AMSL and are based on information concerning the highest elevation in its quadrangle including terrain and constructions (trees, towers, antennas).
The MEF are represented in thousands and hundreds of feet AMSL and are based on information concerning the highest elevation in its quadrangle including terrain and constructions (trees, towers, antennas).
AMann
Well-Known Member
You are right in that it’s related to terrain or obstacle height AMSL , but it shows the safest height to clear that terrain at 300’ above it- the actual height of the terrain or highest obstacles in that area are -300’ below that number.
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AMann
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sdold
Well-Known Member
It's the Maximum Elevation Figure for that quadrangle, it's the highest point in that quadrangle, rounded up to the nearest hundred, and 300 feet is added to that. The highest point's dot is slightly bigger than the other elevation dots. It's not meant to be a "safe" alitude by any means. Dig this:
AMann
Well-Known Member
3160+ 300’ = 3460 AMSL
Flying at 3500’ AMSL would clear the highest point by 340’
Ok, the term I used should have been the “minimum” altitude...obviously any pilot would add a few extra 100’ to that as well to be at least 500’ over it.
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sdold
Well-Known Member
Those numbers are used for planning purposes by pilots flying cross-county, who would typically want to fly a couple of thousand feet over the mountains. They might also be used in other situations like a night flight where you find that you don't have as much fuel as you thought and need to divert. Knowing the elevation of the highest obstacle nearby is useful in those cases, and in neither of these cases would a pilot be looking to "barely" miss the mountain top. Pilots flying within a few hundred feet of mountain tops on purpose don't pay attention to the MEF number because they are watching the mountain under them, or beside them, or looking at the mountain's elevation on the chart as they approach the mountain.
By the way the 300 feet that is added includes obstacles that might not be charted but can be nearly 200 feet tall. Add to that altimeter errors, the improbability of having a local altimeter setting, the allowable error in the altimeter itself, and you can see why it's an obstacle elevation, not an altitude used for flying. If it were meant to be flown, it'd be called an "Altitude", instead of "Elevation." Those exist and are called "Minimum Safe Altitudes", but these aren't them.
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