Is there a file that fsx uses to list airports?

After creating a new airport I've found that several other programs are unable to find my airport with the airport ID. I'm assuming they are looking in a file that lists all the default airports and I just need to append my new airport to the list.
And if necessary, what program will I need to open the file?
I appreciate it.
And if necessary, what program will I need to open the file?
I appreciate it.