Fonte: Times on Line
September 23, 2009
The four reasons why Air France 447 crashed
The disaster of Air France Flight 447 was the result of a preventable mix of human and technical failures, according to a London law firm that is representing families of the victims.
Stewarts Law, which is pressing claims for relatives of over 50 of the 228 dead, presented its argument in Paris today after its experts replicated in a simulator the conditions that were experienced by the crew of the Airbus A330 off Brazil on June 1.
Their findings reflect the consensus in the aviation industry -- and which we have covered here before -- over what went wrong in one of the most worrying air disasters in recent decades.
The official investigation, carried out by the French BEA accident bureau, is far from a conclusion and the black box flight recorders have not been found. Air France and Airbus are on the defensive and saying little. But enough data was transmitted by satellite from the stricken plane to identify with certainty four factors that led to the crash, said John Mahon, an Airbus and Boeing training captain.
-- The aircraft flew into an area of storms which other aircraft avoided by steering around them.
-- The pitot tubes (speed sensors on the front of the plane) suffered faults
-- There was a malfunction in the ADIRU, the three air data computers which feed information to the flight system and the pilots.
-- The pilots may not have had sufficient training to retain control of the malfunctioning aircraft.
"It any one of these issues had not happened to AF 447, the accident would not have happened," said Mahon, who is advising the law firm.
In the A330 simulator exercise, Mahon said pilots retained control of the handicapped aircraft, but they all knew that there was a malfunction. The pilots at the AF447 controls, who are thought to have been the two juniors on the three-man crew, would have been confused by conflicting information from the plane. They were also being thrown around in heavy turbulence at night. The simulator cannot replicate that faithfully any more than the fear that must quickly have gripped the crew.
James Healey-Pratt, the firm's chief aviation lawyer and also a pilot, said: "It is too simplistic to blame the pilots. They are not here to defend themselves. They did the best job they could."
Mahon said the pilots would have lost control of their handicapped plane in one of two situations.
If they entered a climb, the instruments would have erroneously shown increasing speed -- because of the blocked sensors. They would have tried to slow down and that could have led to a low-speed stall. If they were descending, the blocked sensors would have interpreted a decrease in speed. To compensate, the pilots would have increased the descent or added thrust. That could have caused the aircraft to over-speed and lose control.
Since the crash, Air France has signalled concern over its crew's ability to handle high altitude upsets of this kind. It has ordered special training for A330 pilots and called in outside experts to conduct a full-scale audit on its safety procedures. Some Air France pilots are accusing the airline, Airbus and the accident investigators of trying to put all the blame on the crew.
A separate judicial investigation is under way in France. Air France and Airbus will be asked to explain why no action was taken to replace faulty pitot tubes on the A330 series although they had suffered multiple failures over a decade.
The law firm, which has its own priorities, accused Air France of trying to settle with victims families "quickly, cheaply and quietly" in order to avoid having to pay the large sums that they deserved. Healey-Pratt estimated that if settled under European law, the final bill for Air France and Airbus would by about 450 million euros. He suggested that the two companies put one billion euros into a pot to be divided among the families. A similar method was used to avoid litigation after the 9/11 attacks in New York in 2001.
The saga over faulty the pitot tubes continues. The European Aviation Safety Agency today issued a new safety warning. It told airlines to check Airbus sensors from the US Goodrich company. Only two months ago, the same agency ordered airlines to install the Goodrich pitots instead of the ones made by the French company Thales which were the ones involved in all the incidents.
It's worth noting that Captain Mahon - who trains pilots in both Airbus and Boeings -- told me that he does not share the misgivings that some pilots have over the very automated flight systems of the Airbus family. He also pointed out that pitot and air data failures have caused accidents on Boeings in the past.
For an alternative view of AF447 and the plane that some pilots call the Scarebus, I would point you to the latest from John T. Halliday [no relation of our Johnny the rock idol] the well-informed expert on Huffington Post
Posted by Charles Bremner on September 23, 2009 at 05:47 PM in