If an aircraft does not have an FDR, must one be installed to comply with Flight Data Monitoring requirements in EASA countries?
For 20 PAX and more, it becomes mandatory.

https://www.lepoint.fr/sport/le-piper-malibu-un-avion-delicat-22-01-2019-2287804_26.php


  Les boîtes noires sont obligatoires sur les appareils de transport public d'au moins vingt sièges.