Class F Airspace
Class F Airspace is airspace of defined dimensions within which activities must be confined because of their nature, or within which limitations are imposed upon aircraft operations that are not a part of those activities, or both. Flight operations may be conducted under IFR or VFR, and ATC separation will be provided to aircraft operating under IFR, so long as it’s practical.
Class F Airspace is not, however, used in the United States. In the United Kingdom it is used to designate Advisory Routes (ADRs), which are regularly used routes where traffic levels are not high enough to warrant establishment of an airway.
In other countries, such as Canada, Class F Airspace is marked on both VFR and IFR charts. There, class F airspace includes alert areas, danger areas, rocket ranges, restricted areas, forest fire restrictions, and military active areas. Special use airspace may be classified as Class F advisory or Class F restricted, for events like air shows or other such temporary impediments to navigation.