Grid-MORA Charts+ Errors ?

[Piloteprive]

Dear all,

I have switch to another chart provider with my airline (from Jepp to Charts+ NavBlue).
I quite « surprised » to see that almost all Grid-MORA shown in Charts+ are lower than Jepp (up to 2.000 feet sometimes)

A good example is Paris area (LFPO) with a Grid MORA of 1,700 feet. Isn’t the Eiffel Tower around 1,000ft AGL?
The MSA of the airport is around 3.000 feet. I never came across a MSA higher than the GRID-MORA (in the same grid) and the value of 1,700 feet sounds very very low to me for Paris.
Charts+ definition is taking into account terrain or known obstacle elevation (whichever is higher) + 1,000ft or 2,000ft if mountainous area.

Anyone has an explanation?

[AerocatS2A]

Different grids?

[Little One]

You'd need to check the source of the information and how the chart provider has published it.

Generally when taken from State information (AIP or ETOD databases) the charts publish an AMA - Area minimum altitude . The minimum altitude to be used under instrument meteorological conditions (IMC), that provides a minimum obstacle clearance within a specified area, normally formed by parallels and meridians.

Grid-MORA is a Jeppesen specific calculation (It may be a TERPS phraseology as well however ICAO uses AMA in PANS-OPS)
A Grid MORA is an altitude derived by Jeppesen or provided by a State authority that provides clearance of terrain and man-made structures within a section of a chart or database defined by latitude and longitude lines. 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 clearance is 2000 feet in areas where the highest elevations are 5001 feet or higher. Some countries apply different criteria. For decades the primary source used by Jeppesen as the basis for determining Grid MORA values has been a worldwide set of visual topographical charts. In addition, some government aviation authorities provide their own Grid MORAs or equivalent values. Where available, the government provided information has been used. In certain areas the terrain information available on visual topographical charts was incomplete, un-surveyed, or estimated. Traditional topographical charts do not reflect newer sources of terrain data available in the form of digital terrain databases

Generally Survey data for charts is supplied by a National Survey Agency within a State, however many states lag behind in updating the survey data especially on large charts. In my experience Jeppesen tends to have access to more data than what is always published by the State and also uses different criterial for the buffer areas between quadrants thereby giving different altitudes than other providers.

Another thing to be cautious of is sometimes a Maximum Elevation Figure - MEF is published instead. This is usually on VFR charts but I have seen some area charts with MEFs on in the past. MEFs are determined by taking the point of highest terrain within a quadrangle, adding 200 ft for obstacles which are not required to be portrayed, and then rounding up to the next hundred feet