Things You'll Need
Instructions
Navigate to a AI package directory like World of AI or Flight Simmer, both of which host installers that automate the process of adding planes to your game files.
Download an installer and search for a plane model by name, or browse the directory until you find what you want. Click the file link and choose the option to save the file to your desktop from the dialog box that appears. Similarly, click AI packages and save them to the desktop if you aren't satisfied with the default AI.
Open the downloaded file on your desktop to activate your installer and extract the folder's .zip files to C:/Program Files/Microsoft Games/Microsoft Flight Simulator X/SimObjects/Airplanes.
Run "Microsoft Flight Simulator X" and select a mission to play. New traffic will fill the skyline around you, providing a more bustling and relaxing background.