I have been looking at LPMA Madeira and Little NavMap says the elevation is 190 ft. The stock P3d4 version of the airport says that it is at 711 ft. And a PDF of the Jeppesen terminal procedures says the runway elevation is sloped at 147/192 ft.  Is the P3d4 stock version really that far off? And where is LNM reading the elevation from, for its general display under the airport tab?

Hi Jay,

the last BGL in the list on the airport tab will set the elevation for the airport. If that is an altitude correction from e.g Orbx global scenery then this altitude will be used.

Looks like the stock airport in APX43200.bgl is really off. X-Plane and Navigraph both show values around 190 ft.

Alex

Thanks. Okay, I checked further and there are other sources of information online that the stock airport has an incorrect altitude.

However, shouldn't the altitude be taken by LNM from an ALT  BGL file if it exists in /scenery/world/scenery? A number of 3rd party airports have these files which change the elevation and also the name. Or did I misunderstand what you meant by "last BGL in the list..."

The altitude is taken from the BGL in scenery/world if there is no add-on airport which overrides it. The files are read in the same ascending order as the layer id in the scenery.cfg where scenery/world is the very first entry.

The LNM display of all involved BGL files that are used to build or update an airport scenery have the same order. This helps to find errors in the scenery library.

So, you can normally say that the last one in the list wins and overrides all other with the same ICAO id.

If it were only that easy. MS invented the so called delete record. A BGL can contain information that says: "Take the runways of the stock airport and add only the approaches in this add-on BGL".  And this method has a lot of corner cases which are not so well documented.

Alex