Quote from AIP actually is good answer. It is explicit requirement in Spain - to have a two-way while on FP.
Originally Posted by 172driver
You need a FP for flight in/through/into/out of CAS. In the same situation, you need to talk to a controller. Make sense ?
Not necessarily. For example in US - having VFR FP does not mean you need to have a two-way comm in CAS. Can open/close FP through FSS (even through phone) - no ATC contact whatsoever.