While the internal investigation by ITA Airways found grounds to fire the captain, who denies he fell asleep, it did not cite a specific reason for his mysterious radio silence.
The flight was on autopilot, flying at normal speed and altitude and never detoured from its route. Passenger safety was never compromised, airline spokesman Davide D'Amico told The Telegraph.
Inconsistencies in captain's account
ITA Airways, formerly Alitalia, is the new state-owned flagship carrier airline of Italy, which the government reorganised after Alitalia formally declared bankruptcy last Autumn.
In a statement to The Telegraph, ITA said its internal investigation revealed behaviours by the captain that were "not in compliance with procedure" both during the flight and once it had landed.
It noted inconsistencies in the captain's account, such as claiming the blackout was due to problems with the communications system. Those claims were disproven when technicians tested all systems as part of the internal investigation and found no issues.
The airline stressed "clearly and rigorously" that the safety of the flight was always guaranteed, thanks also to elevated technology on board.
Marseille air traffic alert
The disarming detail that both pilots may have fallen asleep on the job might have never been revealed had it not been for the quick work of alert by Marseille air traffic controllers.
The plane had regularly declared its position upon arriving into French airspace at Brest, but then, as the plane passed from Bordeaux air traffic control to Marseille, pilots failed to respond to Marseille air traffic controllers. They had tried in vain several times to contact the pilots about their position.
Alarmed about a potential terrorist incident, French air authorities contacted their counterparts in Rome at 5.21am.
They in turn contacted the ITA Airways central command, who tried to contact the pilots via their satellite cell phones.
French authorities alerted two fighter jets to prepare to fly near the passenger plane to surveil the pilot's cabin. Meanwhile, ITA's command centre began sending messages to the pilots via ACARS, a digital data link system for transmission of short messages between aircraft and ground stations via satellite.
Despite the fact that ACARS messages are displayed on the pilot's monitors, there was still radio silence. More than 10 minutes after repeated attempts to reach them had failed, the pilots eventually responded and went on to land in Rome 20 minutes before their scheduled arrival time.