Airline safety is being compromised by pilot fatigue, BBC News has found.
http://news.bbc.co.uk/1/hi/uk/6236810.stm
Some 32 UK-based pilots said they had flown while unfit. Some blamed the situation on the intensity of work and managers ignoring their concerns.
A separate survey by pilots' union Balpa suggests 81% believe fatigue had affected performance; while 63% are flying more hours than five years ago.
UK-registered pilots may not fly more than 900 hours per year and there is no evidence this is being exceeded.
Industry groups say the airlines have an "exemplary safety record".
'Falling asleep'
Most airlines told the BBC News investigation their average hours had barely changed in the last few years.
The Civil Aviation Authority, which regulates the industry, estimates that pilots are flying 30% more hours than a decade ago but maintains the "finest flight time limitations system in the world" means fatigue is not an issue.
BBC research has found that the demand for more and cheaper flights - particularly short haul - has resulted in some pilots flying more hours and in some cases up to six flights per shift.
The pilots spoke anonymously for fear of losing their jobs.
One said: "I have fallen asleep unintentionally in the air where you close your eyes for a second and realise that 10 minutes have passed."
Another said: "A little minor thing can take your mind off the bigger task."
'Biggest issue'
Following the BBC's inquiries, the UK's largest pilots' union, the British Air Line Pilots' Association, questioned 534 of its members.
In the UK we have some of the most regulated pilot flying hours and duty hours in the world 
Roger Wiltshire, BATA
Some 76% said their response times had been affected by fatigue, 72% said there had been an impact on decision-making skills and 41% they would refuse to fly if fatigued.
But 12% said they would not feel able to refuse duties even if exhausted, while a further 33% said they would refuse - but feared disciplinary action.
Overall, some 79% told Balpa the public should be concerned about fatigue.
Balpa chairman Mervyn Granshaw described fatigue is "the single biggest issue facing aviation".
He said: "At the moment we are not seeing it appear as accidents or incidents but we're getting closer to that point."
Encouraging sickies?
The industry highlights the fact that fatigue has only been cited as a cause in reported accidents and safety incidents on official databases in fewer than one in 1,000 cases.
Evidence gathered by the BBC suggests that fatigue has become a taboo subject and that pilots are scared of losing their jobs if they raise it.
"Whenever I reported that I was completely exhausted the operator says 'Are you refusing to do the duty?'" one said.
"He should not have been asking me, let alone bullying me into doing it."
The BBC has also learned of an incident on a flight to Europe.
The captain told his co-pilot he was exhausted, who suggested he "take five minutes kip - I'll take it from here".
As the captain rested his eyes the aircraft - on autopilot - began to turn, putting it on a collision course with another passenger plane.
Air Traffic Control radioed an urgent warning.
Realising there was no response the captain looked across to see his co-pilot asleep.
How else are we going to get these people out of a situation where they could hazard an aeroplane?
Dr Ian Perry
Corrective action was taken to avert danger. But in the incident report the pilot failed to mention that his colleague was asleep.
"I didn't want to get him into trouble," he told the BBC. "It's not his fault, it's basically what the company are doing."
Dr Ian Perry, one of the country's leading consultants in aviation medicine, says the number of pilots coming to see him who are chronically fatigued has doubled over the last five years to four or five people a fortnight, he said.
"I've been accused by some authorities of encouraging people to report a backache, a headache, a something - so they can have days off to recover from their fatigue.
"I don't deny it. But how else are we going to get these people out of a situation where they could hazard an aeroplane?"
The two groups, which represent the airlines in the UK, deny fatigue affects pilots.
John Hanlon, secretary general of the European Low Fares Airline Association, said: "Europe's low fare airlines have an exemplary safety record and this has been delivered by making safety the number one priority at all times."
He said a scheme is in place so its members' pilots were free to report any issues without having to divulge their identity.
Roger Wiltshire of the British Air Transport Association, said pilots are flying well within their regulated flying hour limits.
"Although short haul pilots are flying more hours than they were that's because the schedules are more efficient," he said.