In a brief post by the Orbx team on the forums, a range of airports for X-Plane 11 has been updated. The small patch is designed to update the ground traffic plugin used by a number of airports in X-Plane 11.50. The update for the 24 airports is free.
You can get the update directly through Orbx Central. Upon loading the software, if you have automatic updates turned on, then the download will automatically detect if you need to install the update.
If you don’t own any of the listed airports down below, it’s likely they will be part of the End of Year sale Orbx is holding, where you can get up to 30% off. You can check that out here.