AFP - French investigators have yet to find out why an Air France jet plunged into the Atlantic with the loss of 228 lives and the inquiry could take another year or year and a half, a top official said Monday.
The prospect of a lengthy inquiry will likely infuriate relatives of crash victims, some of whom have already begun to point the finger at the jet's air speed monitors, which they say were faulty and to blame for the deaths.
Paul-Louis Arslanian, the head of the BEA air accident investigation agency, said the hunt for the destroyed Airbus A330's black boxes would resume in autumn and that other countries would be invited to take part in the probe.
"For the moment, we can't explain the accident," he admitted at a breakfast for aviation journalists. "We still don't know what caused the AF447 accident."
A second BEA interim report will be ready within a "few weeks", he promised, but said this would not offer a definitive explanation, for which the families might have to wait "a year or a year and a half."
Air France Flight 447 from Rio de Janeiro to Paris crashed into the ocean on June 1 and was ripped apart. Just before dropping off radar screens it had emitted a series of automatic warning signals indicating systems failures.
The wreckage of the jet and the bodies of some of the passengers and crew were recovered in deep water 1,000 kilometres (600 miles) off Brazil's coast, but the black box flight recorders remain lost.
Analysis of the error messages indicated a problem with the Airbus jet's "Pitot probes" -- air speed monitors -- but the BEA said in a July 2 interim report only that this was a "factor, not the cause" of the crash.
Since the crash, both the European air safety agency and planemaker Airbus have nevertheless advised airlines to replace the Pitot probes used on the doomed jet with a later and more reliable model made by a US firm.
Relatives of the dead have angrily demanded that Air France and Airbus take responsibility for the crash and French prosecutors have opened a preliminary manslaughter investigation that could lead to negligence charges.
In particular, they have alleged that Airbus and Air France knew about longstanding concerns over the A330's Pitots but had failed to replace them.
"Problems with Pitots have existed for as long as aviation has existed. I don't know that there are any Pitot probes that are guaranteed against any sort of breakdown," Arslanian insisted.
"It's a phenomenon that can happen, for which there are procedure, training, exercises," he added, apparently suggesting the BEA will investigate whether the Air France pilots took the right action when the Pitots seized up.
Pilots say it is extremely difficult to control a modern jet, particularly at high speed and altitude in tropical weather, when the plane's three Pitots are recording conflicting, false or absent air speed data.
Arslanian said the hunt for the plane's black boxes would resume "in autumn" after two previous sweeps failed to find them, one of them seeking a locator signal emitted by the boxes and another using sonar.
"When in autumn? I don't know," he said, adding that other countries would be invited to help in the inquiry in addition to the United States and Brazil which have already been working with the French authorities.
"These preparations for a third phase will be not only with the countries we've already worked with in this inquiry -- the United States, Brazil and Germany -- but also with others," he said.
The third phase of the search will cost more than 10 million euros (14 million dollars), perhaps many times more, he said. Airbus had previously said it would contribute to the costs of the investigation.