Tuesday, September 23, 2008

Maximum elevation figures

Question: I know the maximum elevation figures (MEF) depicted on a sectional chart show the highest terrain and/or obstacles within a quadrant, but can you tell me how the MEF is calculated?

Answer: For man-made obstacles taller than 200 feet, the MEF is calculated by determining the elevation of the top of the obstacle above mean sea level (msl). Then, additional height is added according to a cartography formula to cover a possible vertical error. Finally, the figure is rounded up to the next highest 100-foot increment. For example, if the highest man-made obstacle within a sector is 2,250 feet msl, 100 feet would be added to cover a possible vertical error (2,350 feet). This figure would then be rounded up to the nearest 100 feet and be charted as a 2,400-foot MEF for that sector. A similar process is used for calculating the MEF for terrain or natural obstacles, except that an additional 200 feet is added just in case there is a man-made obstacle on that terrain that wasn't charted because it is less than 200 feet tall. Learn more in the AOPA Air Safety Foundation's Safety Hot Spot, NACO Aeronautical Chart User's Guide.