While most of the current 401 United States National Park Service units are accessible by car, or commercial plane and boat there are 16 NPS units in Alaska where you must charter a bush plane to actually visit the park unit. This is a guide on how to do that.
The 16 "Fly-In" United States National Park Service units in Alaska
10. & 11. Katmai National Park & Preserve13. & 14. Lake Clark National Park & Preserve