A common question is regarding the values shown in the quadrants on the Jeppesen base charts that are used in the AOPA Flight Planner.
On sectional charts, these are MEF values (Maximum Elevation Figure), while on the Jeppesen base charts, Grid MORA values (Minimum Off Route Altitude) are used. There is resemblance in how these two different values are represented on the charts but that is the extent of their similarity.
Below is a detailed explanation that describes the differences between MEF and Grid MORA values and why Grid MORA values are used on Jeppesen charts.
MEFs vs Grid MORAs (In-Depth Explanation of Differences)
MEFs (Maximum Elevation Figures) and Grid MORAs (Minimum Off Route Altitudes) are like apples and oranges. They’re both a type of aeronautical “fruit”, meaning they represent a height or altitude) but that’s where the similarity ends. The complication lies in the fact that MEFs are depicted in a similar way as Grid MORAs using large, superscript text fonts. This similar appearance contributes to misinterpretation and misunderstanding.
An examination of the facts will reveal and substantiate the reason why Jeppesen captures, maintains, applies and outputs Grid MORAs ONLY instead of MEFs.
- MEF and Grid MORAs are based on entirely different Criteria and serve entirely different Purposes.
- MEFs are Figures whereas Grid MORAs are Altitudes.
- MEFs represent a “Maximum” figure whereas Grid MORAs represent a “Minimum” altitude
- MEFs DO NOT provide Obstacle Clearance whereas Grid MORAs DO provide Obstacle Clearance.
- MEFs are shown on FAA-produced Sectional charts for use in VFR flight whereas Grid MORAs are shown on FAA and Jeppesen-produced Enroute/Area charts for use in IFR flight.
- MEFs and Grid MORAs have entirely different Definitions which explain their intended purpose.
Definition MEF (FAA):
Maximum Elevation Figure (MEF): The Maximum Elevation Figures shown in quadrangles bounded by ticked lines of latitude and longitude are presented in Thousands and Hundreds of feet above mean sea level. The MEF is based on information available concerning the highest known feature in each quadrangle, including terrain and obstructions (trees, antennas, etc.)
- MEF definition is published on FAA Sectional charts ONLY. It is not published anywhere in the FAA’s abbreviations, glossary or chart legend publications.
- MEFs are an internal construction of the FAA’s Visual Charting Branch and applied to and maintained on FAA Sectional (Visual) charts ONLY.
- MEFs are NOT provided as source otherwise made available to the public via the FAA’s National Flight Data Center.
- MEFs represent the ‘highest known feature”. MEFs are actual values. MEFs are reference only and do not provide any obstacle clearance, whatsoever.
- By definition, because an MEF is an actual value and does not provide any clearance, if a pilot were to fly at the altitude of a charted MEF, there would be a possibility of the aircraft impacting the top of the “highest known feature” located somewhere within each quadrangle.
Definition Grid MORA (Jeppesen):
Grid Minimum Off Route Altitude (Grid MORA): An altitude derived by Jeppesen or provided by State Authorities. The Grid MORA altitude provides terrain and man-made structure clearance within the section outlined by latitude and longitude lines. MORAs do not provide Navaid signal coverage or communication coverage. Grid MORAs derived by Jeppesen clear all terrain and man-made structures by 1000 feet in areas where the highest elevations are 5000 feet MSL or lower. Grid MORA values clear all terrain and man-made structures by 2000 feet in areas where the highest elevations are 5001 feet MSL or higher.
- Grid MORAs are intentionally designed to support IFR flight
- The FAA equivalent of the Grid MORA is the Off Route Obstacle Clearance Altitude (OROCA).
- The FAA OROCA value provides 1000 foot and 2000 foot obstacle clearance within a referenced grid area, but the clearance is predicated on the FAA’s own designated Mountainous Terrain Areas instead of a terrain elevation of 5000 foot MSL
- The FAA’s OROCA is intended for use in IFR flight.
- Where a State provides a Grid MORA or an equivalent value intended for IFR use and which provides obstacle clearance, the State provided value is used by Jeppesen.
- By definition, because a Grid MORA is a value which includes 1000 or 2000 foot clearance, if a pilot were to fly at the altitude of a Grid MORA, in either VFR or IFR flight, the aircraft would NOT impact any terrain or obstacles located in the referenced grid.
For all the reasons outlined above, Jeppesen maintains and applies Grid MORAs ONLY. While the scope of this policy was originally based on the intended use to support IFR flight, it has been determined that Grid MORAs serve the same purpose and add similar value for use in applications that support both IFR and VFR flight operations.
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