Pilots at a budget airline involved in a fatal crash earlier this year have said they are over-tired and being asked to work too many hours, according to reports.
A set of leaked safety reports seen by The Guardian show pilots at FlyDubai reporting that their rota often leads them to be fatigued.
In March the airline's flight FZ981 crashed in the southern Russian city of Rostov-on-Don, killing all 62 people on board after trying to land in strong winds.
United Arab Emirates-based FlyDubai was set up in 2008 and flies to 85 destinations across the Middle East, eastern Europe, east Africa and south Asia, but not the UK.
In a statement given to The Guardian the airline said its first priority was safety and that it would never ask crews to operate outside legally-permitted hours.
The newspaper said it had seen the air safety reports of 413 FlyDubai flights written in March and April 2016. Pilots describe concerns about fatigue in more than 40.
In one, regarding a flight very soon after the FZ981 crash , a pilot notes that he flew 62 hours over seven days, when the maximum duty limit is 55, upped to 60 in case of unforeseen delays.
"I raise this, mostly for the safety of our crews," the pilot wrote.
"We are often rostered close to the limit anyway, and the crewing department do need to be careful with what they are asking people to do."
One pilot describes some rostering as "illegal" and said the way rotas are organised was leading to a "dangerous situation".
In another, a pilot reports that a senior crew member had to be reprimanded for falling asleep in-flight.
The British Airline Pilots' Association said fatigue was the number one safety concern raised by pilots.
A spokeswoman said: "Reports of fatigue from pilots are on the increase and BALPA is working hard in negotiations with airlines to persuade them to accept those reports as warning signs and reach agreement with us on safe working hours.
"The concerns expressed about FlyDubai should be taken extremely seriously.
"If the company is correct when it says it only rosters within the rules, then it just goes to show that the rules are clearly not good enough - a point BALPA has previously made to UK and international regulators."
FlyDubai told the Guardian its fatigue policy was designed "openly and proactively" to provide a blame-free structure for crew to report when they felt unfit to fly.
A statement said: "FlyDubai rigorously adheres to all regulations set out by the regulator, the General Civil Aviation Authority (GCAA) and operates to the highest standards.
"As part of our transparent reporting environment we investigate each of these air safety reports (ASRs) to conclusion to understand if they have any operational irregularities and any safety implications."