cabrini

Hi everyone, i was reading about GRID MORA! And we all know that "by 1000ft in areas where the highest elevations are 5000ft MSL or lower. MORA values clear all terrain and man-made structures by 2000ft in areas where the highest elevations are 5001ft MSL or higher" ....

According to the text above, for example, if the highest elevation is 5100ft the GRID MORA will be 7100ft, right?

So there won't be any GRID MORA from 6100ft to 7000ft!!! is that correct???
But I've seen some on charts!!

EMIT

Probably depends on the chart maker, Cabrini.
Following quote from LIDO, do not have Jeppesen definitions available.

1.6.2.11.1.8. Minimum Grid Altitude (MGA)
The MGA represents the lowest safe altitude which can be flown off-track. The MGA is calculated by rounding up the elevation of the highest obstruction within the respective grid area to the next 100ft and adding an increment of
▪
1000ft for terrain or obstructions up to 6000ft; or
▪
2000ft for terrain or obstructions above 6000ft.
Example: ELEV of highest obstruction: 6345ft; rounded up = 6400ft + 2000ft buffer = 8400ft MGA
MGA is shown in hundreds of feet. The lowest indicated MGA is 2000ft. This value is also provided for terrain and obstacles that would result in an MGA below 2000ft. An exception is over water areas where the MGA can be omitted.

A Squared

If you look at the Glossary in Jeppesen's CHart guide, the definition you quoted is part "a". part "b" states: b. GridMORA (State) altitude supplied by theState
Authority provides 2000ft clearance in mountainous areas and 1000ft in non-mountainous areas.

There are mountainous areas with elevations lower than 5,000 ft.

megan

A Squared, if that is the case, what do they define a mountain as being? As far as I'm aware there is no universally accepted definition of "mountain".

A Squared

Well, in the US there are designated mountainous areas. I don't know the precise criteria they use for that, but at some point, The Powers That Be have decreed that this area bounded by these geographic points shall be mountainous .

corrigin

Cabrini,

For Jeppesen definition, kindly look at page 11 in Glossary.

http://ww1.jeppesen.com/documents/av...ry-legends.pdf

Also:

http://ivao.aero/training/documentat...t_altitude.pdf

.....and:

http://ww1.jeppesen.com/download/aopa/dec-aopa.pdf

Dusty_B

You could have terrain of 4900' and an obstruction of 1200', giving a MORA of 6100'.

megan

Thanks corrigin, the Jep link worked fine, and they define it as,

cabrini

Thank you all for your answers guys! Thanks to corrigin for the links.

I`ve never heard about this "On Jeppesen charts, all MORA altitudes which are 6,000 feet or lower have an obstacle clearance of 1,000 feet. If the MORA altitudes are 7,000 feet or greater, the obstacle clearance is 2,000 feet." Very interesting in fact!

I thought it was only about lower or greater than 5000ft!

And it is not mandatory to have increments of certain 1000ft or 2000ft, it can be 1200ft,1600ft,2100ft, it will depend ... That`s it?

Just to make sure that I've understood everything that you all said!