This site is being deprecated.
Please see the official X‑Plane Support page for help.
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My guess is that your system may not be sufficient to handle X-Plane 11 at your current Graphics settings. Stuttering and loss of FPS is usually due to CPU limitation. As you approach an airport, more items and details need to be rendered. You can try lowering the “Number of World Objects” in Graphics Setting to see if it could help to improve smoothness.
This site is no longer being actively maintained.