On X-plane website, I saw we can download free demo. The installer is only 20 MB so I think the included data file may be the slimmed-down version that does not contains 7 millions records. But it at least gives a sample data for testing.
Can anyone check it to make sure it has the same file format as what @JLWest mean?
Yes it has the same format.
I never downloaded the demo but bought the product. It is my understanding that the demo is the same as the product.
There is one possibility to that being a slim down version of an Apt.Dat. I believe the demo will only let you fly within a 100 or so miles of you location. So I wouldn't be able to start at Heathrow England because I live in Phoenix. They would have to do that thru the apt.dat file. I get that from reading threads where guys are complaining of not being able to start in wherever or fly to somewhere. Always turns out. Do you have the demo. And low and behold there are more than one apt.dat files on a typical installation.
If you buy a payware airport for your custom scenery dir say a MisterX's KLAS you will get two supplied by him. One with ground (Static Aircraft) and one with out. All custom scenery airports come with their own apt.dat file. In my case I have about 30.
So in summary:
There is the Global: 7.9 million records. that I'm trying to work with.
Local Global in Custom Scenery: C:\X-Plane 11\Custom Scenery\Global Airports\Earth nav data\apt.dat This file is smaller. About 163,959KB. It is unclear what the use of this apt.dat file is but info suggest it is used as a small backuip should your global 7.9 mil become corrupted. If they can't find your desired location in the secondary they display a message of corrupt file and crash to the desktop.
And then all payware airports supply there own apt.dat file but must meet X-Plane spec because X-Plane renders and loads.
Here is the short and dirty of how it kinda of works:
When you stat X-Plane you have to select a starting airport from a list box of 3,700+ airports. You can not start from an airport not in the system.
If I specify KLAX it checks my Custom scenery dir for a KLAX. If there that's what it loads and uses the KLAX apt.dat file supplied buy the designer.
If not it goes to the global. The 7.9 mill and reads out the KLAX records.
No here is where the magic happens. I don't have anywhere on my system 3,700+ airport designs with buildings. The apt.dat only carries flat earth, line and signs, lights and static aircraft. No buildings or towers. Supposedly there in somekind of markup file somewhere.