Instructions
Navigate to the "FlightGear" website and download the latest version of the game. This will ensure that it is compatible with all the free planes available.
Double-click the setup file after the download is complete to install the game. Select a path outside the "Program Files" directory if you are running Windows Vista or higher in order to prevent issues with the user account control when you add the planes. Use "C:\FlightGear" as the install directory for best results.
Navigate to the plane download section of the "FlightGear" or "FlightGear Planes" website and select the plane you want to install.
Specify the "Aircraft" directory inside the "FlightGear\Data" folder as the destination for the download. For example, if you installed "FlightGear" to "C:\FlightGear," then the destination would be "C:\FlightGear\Data\Aircraft."
Navigate to the "Aircraft" folder after the download is completed and right-click on the "ZIP" file. Select "Extract All" from the menu. Your new plane will now be installed and ready for use in the game.
Start the game and select the new plane from the "Aircraft" menu.