Workers in Recife, Brazil, unload debris from the crashed Air France flight AF447 in June 2009. Airbus, which made the jet, is facing manslaughter charges in France in connection with the crash. Eraldo Peres/Associated Press

A French judge filed preliminary manslaughter charges Thursday against Airbus over the 2009 crash of an Air France jet — opening a rare criminal investigation against a corporate powerhouse.

The order from Judge Sylvie Zimmerman targeting the European aircraft manufacturer centres on the June 2009 crash into the Atlantic of an Airbus A330 bound for Paris from Rio de Janeiro, which killed all 228 people on board.

Airbus chief Thomas Enders told reporters the company disagreed with the judge's "premature" decision, especially in light of the still-unsolved mystery about the crash.

The preliminary charges, which allow for further investigation, came after Airbus lawyers met with the judge on Thursday. Enders said Airbus will continue to co-operate with the probe.

Charges against Airbus, the world's top planemaker, are unusual but not unprecedented. Airbus employees have been charged in France in previous crashes.

False readings before crash

Air France flight 447 went down June 1, 2009, amid an intense, high-altitude thunderstorm. Automatic messages sent by the plane's computers show it was receiving false air speed readings from sensors known as pitot tubes.

Investigators have said the crash was likely caused by a series of problems, and not just sensor error.

Specialists are launching a fourth undersea search effort next week for the plane's so-called black boxes, or flight recorders.

"We are convinced if we find the black boxes we'll be able to reconstruct what really happened on this tragic flight Air France 447," Enders said.

Airbus officials said the search is a company priority.

Robots to be used in search

Air France and Airbus will finance the estimated $12.5 million cost of the new search, in which three advanced underwater robots will scour the mountainous ocean floor between Brazil and western Africa, in depths of up to 4,000 metres.

Already $27.5 million has been spent on three previous search attempts that failed to find Flight 447's voice and data recorders.

The exact role the sensors played in the crash may never be known without the flight recorders.

Airbus knew since at least 2002 about problems with the type of speed sensor that malfunctioned on the doomed jet, The Associated Press has reported.

But air safety authorities did not order the replacement of sensors until after the crash.

The tubes, about the size of an average adult hand and fitted to the underbelly of a plane, are vulnerable to blockage from water and icing.

Experts have suggested that Flight 447's sensors, made by French company Thales SA, may have iced over and sent false speed information to the computers as the plane ran into a thunderstorm at about 10,600 metres.