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Sailors from Brazil's navy recover debris in June 2009 from the Air France flight 447 that plunged into the Atlantic Ocean. Picture: AP Source: AP 
Source: The Australian WHEN Air France flight 447 took off from Rio de Janeiro bound for Paris in June 2009, it was on a collision course with an equatorial storm over the Atlantic Ocean. On board were 228 passengers of 30 nationalities, including 11-year-old British boy Alexander Bjoroy on his way back to school after a holiday with his family in Brazil.
It was a routine overnight flight. But that storm was creating an unusual volume of ice at 10,000m. Either the pilot misjudged the ferocity of the storm or the plane's sensors became clogged with ice that fed false information to the cockpit.
Precisely what happened during that terrifying ordeal can be understood in part from transmissions from the plane sent automatically to a land-based computer. But for the details, air-crash investigators need to find the black boxes that could provide a second-by-second account.
With the weekend discovery of the wreckage, that may now be possible.
While the black boxes could explain the disaster, retrieval of the wreckage - with bodies still trapped within - will cause anguish among the relatives who are torn between the need to know what happened to their loved ones and their desire to treat the site as a final resting place.
The wreckage was located at the weekend by robots at a depth of nearly 4km. Salvage workers will soon start pulling up from the ocean floor the bodies of passengers and the wreckage of the four-year-old Airbus 330-200.
"There is a good chance" of retrieving the recorders, says Jean-Paul Troadec, director of France's Air Accident Investigation Bureau. "We know where the recorders are attached to the fuselage, we are confident we can still find them if they are still attached."
But he warns the boxes may have been dislodged from the fuselage.
A spokesman for the families believes the discovery of the wreckage and its retrieval will spark anguished debate.
"There is the question of identifying the bodies. We don't know what state they will be in," says Robert Soulas of Help and Solidarity, an association of relatives of crash victims.
"It's very encouraging for us who have been without news and now have hope of retrieving the bodies. We can finally bury them," says the president of the association, Nelson Marinho.
Other relatives face the bitter-sweet prospect of disturbing a gravesite or bringing the bodies to the surface for burial.
French Transport Minister Nathalie Kosciusko-Morizet says some bodies have been seen in the remains of the cabin, photographed by three Remus unmanned submarines operated by the company that found the Titanic.
"There are still some bodies in the section that has been found," Kosciusko-Morizet says, adding that "some identifications" could be possible. Salvage operations could begin within a month.
After nearly two years resting in the cold temperatures of the seabed, the bodies are probably fairly well preserved because
in those conditions, natural decaying processes should have been delayed.
However, it is possible that deep-sea marine life may have fed on the remains.
If the bodies can't be physically identified, clothing, wallets and passports could help in the process. Fingerprint identification is considered an unlikely option.
The best and most reliable means of identification is DNA matching, but even this supposedly reliable method has been found wanting. Previous experience of testing bodies immersed in water for long periods has resulted in failure to find matches.
The Guardian newspaper quotes Derrick Pounder, a professor of forensic medicine at Dundee University, querying efforts to recover partial remains.
"The issue is whether it is appropriate . . . it is a grave on the seabed and it is possible to have wreath-laying ceremonies at sea for those who are grieving. If you know who was on the flight, you know who is dead and where their grave is. If you start to recover the bodies, you may end up opening Pandora's box."
The key for investigators is to find the black box, Troadec says. "The favourable news is that the debris area is relatively concentrated. And this gives us hope of finding the black boxes."
Whether the flight data can be retrieved after so long immersed in water is an unknown.
The established conjecture is that flight 447 was brought down by a terrifying mix of weather and technological weakness. At 10,000m, the margin for error in controlling an airliner is tiny.
In the aftermath of the disaster, it was understood clearly that the aircraft had encountered a storm and severe turbulence. This much information was transmitted at the time.
Soon after, its automatic communications and reporting system showed that the plane's autopilot disengaged. At about 10,000m, with storm winds raging and the plane buffeted on all sides, the crew struggled to control the 230-tonne aircraft.
The pilot would have been looking at two computer screens and numerous displays. He had rudder pedals but no traditional hand controls. The A330 is equipped with a small joystick to one side, similar to a computer-games console. The pilot flies using electronic signals.
"It's tricky. At altitude, big planes wallow about," says Roger Guiver, a former airline pilot who explained what the Airbus pilot was experiencing at the time. "It's like trying to steer the QE2 with a 2ft [60cm] rudder."
The margin for error is small in the best of conditions. In a storm, things can go wrong if pilots don't have the right data, particularly their airspeed.
Speed is a crucial factor. The thinner the air, the more speed is needed for the wings to maintain their lift. If the plane is too slow, it stalls; that's elementary aerodynamics. The faster air passes over the wing, the more the centre of lift moves backwards, pushing the nose of the plane down. Too fast, and the plane can nosedive.
At high altitude the gap between those two critical speeds gets narrower and narrower. That's the so-called "coffin corner", and possibly the crisis faced by flight 447 as the plane flew through the thunder clouds.
Soon after the accident, it was theorised that the crew did not know how fast they were travelling. Automatic signals were giving inconsistent readings of the plane's speed.
The questions posed were: did the crew or computer mistakenly think there was a danger of stalling? Did they power up, tipping the plane out of control and tearing it apart in the turbulence? Or did a violent updraft simply drive them too close to coffin corner?
A bomb or lightning strike were eliminated as possible causes. Instead, human error or incorrect flight data were canvassed.
The Rio-Paris route passes through an inter-tropical convergence zone where humid trade winds create storms. Weather maps for that night show numerous cumulonimbus towers rising to at least 15,000m, with thunderstorms and severe turbulence. But it was not exceptional.
When flight 447 went out of range of land radar, it meant the pilots were relying on their onboard radar to avoid storms. It's possible the pilots failed to spot the storm ahead.
Perhaps they tried to fly above it where, at high altitude, water turns to ice crystals making radar less effective.
It seems unlikely to have been pilot error alone, especially since the crew of flight 447 was experienced and the A330 has had an excellent safety record since it came into service in 1993. Nevertheless, it has suffered unnerving incidents. For example, in October 2008, a Qantas A330 was flying at 11,000m over Western Australia when it suddenly pitched nose-down, injuring more than 100 passengers. A report on the incident found one of the plane's computers had "started providing erroneous data".
Onboard computers rely on data from external sensors. One that supplies information on airspeed is the pitot. If it gets blocked by ice, it could supply incorrect information to the fly-by-wire system. This is theorised as the most likely reason for the crew of flight 447 to misjudge the plane's actual airspeed.
In 2001 a directive for the A330, issued by the US Federal Aviation Administration, said: "Unreliable airspeed may be caused by a radome [radar housing] destruction or obstructed pitots."
Perhaps the pitot iced up and confused the aircraft's system. It's clear the plane's autopilot disengaged and system failures followed. Automatic transmissions reported multiple faults. Two minutes later, both flight control computers failed. Back-ups also failed, so something drastic happened to send the plane spinning out of control. Four minutes after the autopilot disengaged, the cabin suddenly depressurised, perhaps with explosive force.
Whatever happened, the passengers must have been terrified. It was dark, lightning was splitting the sky and the aircraft was shuddering in the turbulence. Sudden decompression, exposing passengers to temperatures of minus-30C or below, would have caused them to lose consciousness well before the plane hit the water.
The wreckage was found near the plane's last known position in a mountainous area of the seabed.
"The fact that the debris is concentrated in a relatively small area favours the hypothesis that the plane did not break up in flight. The plane was intact when it hit the sea," a source involved in the search says.
The speed sensors used on the A330 fleet have been replaced.
But the riddle will not be solved conclusively unless the black box is found.
Air France and Airbus - which are being probed for alleged manslaughter in connection with the crash - are paying the estimated $US12.7 million ($12.2m) cost of the search.
The Times
Additional reporting; agencies
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