Hi,

On a previous visit we were told that it is mandatory to get
permission to enter

Class F is temporarily activated (usually when IFR departures or
arrivals occur). If not active there is no difference to Class G.

Even if active it is still uncontrolled airspace but with higher
minimums. IIRC they are 5km visibility, 1500m lateral and 1000ft
vertical separation from clouds.

So when weather is above those minimums you can enter. There is no
clearance required. Nor do you have to be on the frequency. Nor is there
any separation from other traffic.

If below minimums AND the airspace F is active you cannot enter. That
is the only case where you legally need to know the activation status
and thus have to get on the phone or radio to find out.

In practice it is a good idea to inquire in any case and if active
avoid.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn
http://www.marian-aldenhoevel.de
"Success is the happy feeling you get between the time you
do something and the time you tell a woman what you did."