Radio communications were performed in Italian and English language.
ATC personnel did not realize that Cessna Citation was on taxiway
Romeo 6.
The ground controller issued a taxi clearance toward north (main) apron although the reported position S4 did not have any meaning to him.
Instructions, training and the prevailing environmental situation prevented the ATC personnel from having full control over the aircraft movements on ground.
The aerodrome standard did not comply with ICAO Annex 14; required markings lights and signs did not exist (Romeo 6) or were in dismal order and were hard to recognize especially under low visibility conditions (Romeo 5 - Romeo 6), other markings were unknown to operators (S4).
The competence maintenance & requirements for recent experience for ATC personnel did not comply fully with ICAO Annex 1.
The Low Visibility Operations implementation by ENAV did not conform to the requirements provided for in ICAO Doc 9476.
No functional Safety Management System (SMS) was in operation.