The airport is protected by class E airspace - this allows VFR traffic entry without prior permission, and without any need to speak on the radio. however, ATC can upgrade the airspace to class F when IFR traffic is about to arrive or depart by making a radio broadcast, after which radio contact is mandatory. By implication all VFR traffic entering the airspace whilst it is class E must maintain a listening watch on the appropriate frequency.
Are the rules regarding Class F different in Germany to the UK then ? I thought that airspace classes had the same regs across Europe.