Here are the regulations on opening and operating private aerodromes. Shouldn't take long to absorb, as it is all covered in one order, four royal decrees and a correction to a royal decree.
Normativa-Aeródromos y helipuertos de uso restringido-Aeropuertos-AESA-Agencia Estatal de Seguridad Aérea - Ministerio de Fomento