mine shows the addition for MEF is not 300' but a variable amount
What I was taught is that the MEF is actually the highest of the following two:
- Altitude of the highest obstacle, rounded up to the nearest 100'.
- Altitude of the highest terrain, plus 300' to account for an unknown obstacle, rounded up to the nearest 100'. (There is no notification requirement for obstacles up to 300'; that's why we add 300' if we use the highest terrain figure.)
The MSA is then 1000' above the MEF, or 2000' above the MEF in mountainous terrain.
You can calculate these numbers in a number of ways:
- Take your route, look left/right 5 or 10 miles, and work from the highest marked obstacle or spot height
- Take the grid MSA/MEF that's written on the chart for every 1/2 degree lat/long.
- Take the maximum elevation figure that applies to the whole chart - it is usually listed somewhere up front or in the legend.
In any case, if there are MEF and/or MSA grid numbers on the map, then the legend should somehow explain how these were calculated. The Jeppesen VFR+GPS, for instance, lists this in the legend:
Minimum Grid Area Altitude
These figures are shown within grids defined by each half degree of latitude and longitude. This value provides clearance of all terrain and obstacles by 1000ft in grids where the highest point is 5000 ft MSL or lower, and by 2000 ft in grids where the highest point is 5001 ft MSL or higher.
Further down it also shows the elevation of the highest spot on the map (in ft MSL) and the location where this can be found.