The captain of a FlyDubai plane which crashed in Russia killing all 62 people on board had resigned from the airline, according to the BBC.
Three other pilots, speaking anonymously to the news organization, said he had quit due to fatigue.
Cypriot Aristos Sokratous was serving out his three months notice when the Boeing 737 he was piloting crashed in Rostov-on-Don.
His colleagues said he had given fatigue and lifestyle as his reasons for wanting to leave.
FlyDubai, a budget carrier with a hub in Dubai, said it was important not to speculate about the cause of the crash ‘not least out of respect for the families involved’.
Independent investigators believe poor visibility and high winds might have contributed to the accident, which happened as the jet was trying to land.
FlyDubai released a further statement in which it said: "For FlyDubai the safety and welfare of our flight crew and cabin crew is of primary importance. The whole aviation industry is heavily regulated.
"We strictly follow authorised flying duty time regulations in compiling duty rosters, with special attention paid to the variables which affect our crews including report times, previous duty and the number of days off.
"If a member of flight crew feels that, for whatever reason, they have not been able to get enough rest before starting a shift, our Safety Management Systems (SMS), encourages pilots to declare themselves unfit to fly."