Hello
I’m currently working with “Grid MORA” and I noticed that the values for Navigraph (same as LittleNavmap) and https://skyvector.com/ (same as Aivlasoft EFB2) are different.
it’s not just the classification but also the values. If I take the highest number in the four fields with skyvector, I don’t get the same value as with Navigraph. For example, on the right from LEBL to LEGE the highest value for skyvector is 6.5 and Navigraph gives 7.6.
What is true and why?
Thank you very much for the clarification
Hi,
MORA values are generally not provided in government source an are calculated by the data supplier. There are, however, some governments that do provide off route altitude data and a data supplier may elect to use the government source values in their data services.
So, without knowing what data provider SkyVector is using, I would say both are correct so far. Possible that the Jeppesen calculated values are a little bit more higher, but better higher than to low. Again, there are several sources available and GridMora is not a source what the government will offer - so you can use 3rd party sources or as in our case, our data supplier calculates it.
Hope that helps
Richard
Hi
Thank you for the detailed feedback.
Then is this also the case in “real” life, that every chart application shows different values?
Hi,
MSA and Grid Mora are two different things (at least for different purposes), even though they look the same. Grid Mora is a 1 x 1 degree grid box and will be used by Jeppesen for obstacle-clearance altitude (for the complete block).
MSA is normally a circle of 25NM (plus, I guess, 5 miles of buffer) around a navigation facility/airport.
So, the MSA is a much smaller area than a Grid Mora Box. So when, i.e., an airport is located on an edge of a Grid Mora box, and the radius overlaps these Grid Mora boxes, it could be possible that the MSA (due to a higher obstacle) is higher than the Grid Mora.
That obstacle would affect the MSA, but not necessarily the Grid MORA of the grid containing the airport.
So, Grid Mora < airport MSA is possible and not inherently an error.
Cheers
Richard
Thanks for your reply.
The question here is why is the Grid mora 2500 ft on Navigraph chart while it is 3200 ft on FAA chart ?
Do they have different calculations ?
Yes, the calculation is different. For Jeppesen, it is Grid Mora, and for the FAA, it is Off-Route Obstacles Clearance Altitude.
What I know is that both use the same underlying data, but, i.e., FAA uses the highest known terrain or obstruction plus 1000 ft in non-mountain areas, and 2000 ft in mountain areas. For Jeppesen-derived values, the 5,000 ft elevation threshold determines whether the clearance is 1,000 or 2,000 ft.
So, they calculate it in two different ways, and I assume that’s why there are differences.
Cheers
Richard
Thank you, that was what I meant 
… not a native speaker, sorry …
In the meantime, I have checked the data source and … I have this line in our data:
S AS N39W090 032032028032030032031029038052071057048040027022015010010010010010010010010010010010010010 009891301
N39W090 is the starting point of the grid (lower left corner)
After that, you have 30 entries to 3 numbers, and in the first place, you see 032, which means 3200 feet - what you have written.
I´m not the responsible person for the charts, so I can´t really say where the 2500 ft comes from. When I check our source, I would also expect 3200 ft, not 2500 ft, at this point.
I will forward this question to the right person for the charts; they may be able to analyze where the 2500 ft comes from.
Cheers,
Richard