I think Canada uses Class F in the way intended by ICAO =>
Class F airspace is special use airspace.
Any Class F zone will be designated either CYR, CYD, or CYA. CYR stands for
restricted, CYD means
danger (usually used for CYR areas over international waters), and CYA stands for
advisory. CYA zones will also have a letter identifying the type of activity in the zone: A –
aerobatics, F – aircraft testing, H –
hang gliding, M – military, P –
parachuting, S –
soaring, T – training.
- For entry into a CYR or CYD zone, an aircraft needs the permission of the operating authority. Pilots may enter CYA zones at their discretion, but are encouraged to avoid them unless taking part in the activity.
It is the nature of the activity that takes part in these airspaces that precludes normal ATC separation being either desired or appropriate.
The UK has not used Class F since 2014: (
https://www.nats.aero/ae-home/introduction-to-airspace/ )
