Pilot fatigue 'one of the biggest threats to air safety'
It was a cold winter night on 12 February 2009 when Continental flight 3407 took off from Liberty International Airport in Newark, New Jersey, on what should have been a fairly routine flight.
But five miles north-west of its intended destination in Buffalo, New York, the plane stalled before plunging into a house below, killing both the pilots, as well as two flight attendants, all 45 passengers and a man on the ground.
The pilots had failed to properly respond to cockpit warnings that the plane was moving too slowly through the air, with captain Martin Renslow raising the plane's nose, slowing it even further.
The accident report said that ahead of the flight, both pilots had long commutes and slept in the crew lounge, instead of a hotel.
Tiredness was cited as one of the factors in the crew's failure to respond quickly and appropriately to the aircraft's loss of speed.
Pilot fatigue has long been a concern, and the European Aviation Safety Agency (EASA) recently proposed new EU-wide rules setting limits on the duration that pilots could fly and be on duty.
If signed into law, it would be the first time that airlines across the continent have had one set of shared rules to ensure passenger safety is not compromised by tired pilots.
But pilot unions and the House of Commons Transport Committee argue that the proposals do not go far enough and could put passengers in danger.
Aviation accidents are still extremely rare, but when they have occurred, figures show that 80% are a result of human error, with pilot fatigue accounting for 15-20% of human error in fatal accidents.
Fatigue leads to slower reaction times and impaired concentration and decision making.
There's also the danger of falling asleep.
A survey by the British Airline Pilots' Association (Balpa) of 500 of its members showed 43% had involuntarily fallen asleep in the cockpit, and of those, 31% said that when they woke up the other pilot was also asleep.
'Like being drunk'
Prof Torbjorn Akerstedt, a sleep expert based at Karolinska University in Sweden, said that most people are able to stay alert for 16 hours during the daytime, but that reduces at night.
It has been well established scientifically, Mr Akerstedt said, that the impairments a pilot experiences landing a plane at 05:00 in the morning are the equivalent of having a blood alcohol level of 0.08%, which is the same as the UK's drink-driving limit and over the legal limit in many other countries.
David Learmount of Flight Global believes that "allowing pilots to get dangerously fatigued is like legalising pilots flying when they are drunk".
Just last year, 16 passengers on an Air Canada flight were injured as a result of pilot fatigue. The co-pilot woke disorientated from a nap and, believing that the plane was going to collide with another aircraft, put the jet into a dive, sending passengers sprawling in the cabin.
What the pilot thought was another plane was actually the planet Venus.
The UK's aviation regulator, the Civil Aviation Authority, has supported EASA's recommendations, saying passenger safety will not be compromised. If approved, they are expected to be fully implemented by 2015.
But critics, including Balpa and the European Cockpit Association, say there is a possibility that on rare occasions, pilots who have been on standby could potentially be landing a plane after being awake for 22 hours.
That was disputed by EASA's head of flight standards, Jean Marc Cluzeau. He said that pilots on standby can still sleep and rest, so would not be working until they are called to fly as cover for a fellow pilot.
Another complaint from the unions is that the new rules state that pilots can fly for up to 11 hours overnight, which contradicts scientific research showing that 10 hours should be the maximum.
Mr Akerstedt was one of the scientists consulted on the proposals but he told the BBC that he felt his advice had been ignored by EASA.
The issue has always been contentious, with airlines trying to turn a profit and pilot unions making sure that their members are not being pushed beyond their limits.
Mr Learmount said most of the new rules improve current legislation, but one or two could potentially be abused by unscrupulous airlines to make pilots fly whilst dangerously fatigued.
In the wake of the Continental flight 3407's crash, US regulators lowered flight time limitations considerably.
The father of one of the victims of Continental 3407, Scott Maurer, recently wrote to transport secretary Patrick McLoughlin urging him to reject EASA's proposals.
"What value do you place on your loved ones?" Mr Maurer's letter said.
"How do you value the loss that would occur if a commercial aircraft crashed into a crowded arena because of fatigued pilots? Before our tragedy I would likely have said: 'What are the chances that will happen? One in 20,000,000?'
"Sadly, I now know that fatigued pilots increase those odds exponentially."