The captain of the FlyDubai jet which crashed in Russia last Saturday was due to leave the airline over fatigue, colleagues have said.
All 62 people aboard the passenger jet flying from Dubai to southern Russia were killed when their plane crashed on its second attempt to land at Rostov-on-Don airport.
Speaking anonymously to the BBC, the pilots said fatigue was a contributory factor in the accident.
Earlier, one pilot reported falling asleep at the controls from exhaustion.
However, FlyDubai says these claims relate to "confidential information".
"We are unable to disclose confidential information relating to our employees," a spokesperson said.
"It is important, not least out of respect for the families involved, that we do not speculate about the circumstances of this tragic accident, whilst the independent investigating authorities carry out their work.”
Air tragedy: 62 perish as Dubai plane goes down in Russia
Poor visibility and high winds are also being considered as the cause of the accident.
FlyDubai staff members said the captain, Cypriot Aristos Sokratous, had already resigned and was serving out his three-month notice.
"This crash was very close to home," a FlyDubai pilot told the BBC. "I don't want to speculate on what caused the crash, but I think fatigue must have been a contributory factor. I'm also not surprised it happened.
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"Crew are overworked and suffering from fatigue. It is a significant risk.
"Staff are going from night to day shifts without enough rest in between. I would say 50% of the airline's workforce are suffering from acute fatigue.
"I raised it with a senior member of staff at the airline who said 'we don't have a fatigue issue at FlyDubai'."
"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," the pilot added.
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"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."
Fatigue has been linked previously to a number of previous high profile aviation incidents, which includes the TransAsia flight that crashed in a heavy storm on Taiwan's Penghu island on July 2014.
Officials say the cockpit voice and data recorders recovered from the crash scene were badly damaged, unlikely to reveal much data.