A fourth hunt for the black boxes and wreckage of Air France flight 447 is under way, French officials said Wednesday.
Searchers hope any discovery might help them learn why the jet carrying 228 people dove into the Atlantic ocean during a turbulent storm two years ago, killing all on board.
The French accident investigation agency BEA is overseeing the search and said on its website that a boat carrying three advanced underwater robots left a port in the northeastern city of Recife late Tuesday night.
The robots will scour the mountainous ocean depths between Brazil and western Africa where the plane went down, looking for wreckage of the Airbus A330 that crashed June 1, 2009.
The jet crashed after running into an intense high-altitude thunderstorm while en route from Rio de Janeiro to Paris. No definite cause has been found.
While the BEA is responsible for the search, they say that experts from the U.S.-based Woods Hole Oceanographic Institution, who have participated in previous searches, will have the "operational responsibility" for the new hunt.
The search is being targeted in area of about 3,900 square miles (10,000 square kilometers), several hundred miles off Brazil's northeastern coast, and could last until the beginning of July, the BEA said.
David Gallo, a director of special projects at Woods Hole who is leading the search, said that only a small percentage of the area has ever been explored, making the search even more difficult, though he is confident that if the wreckage is in the target area, it will be found.
Air France and Airbus are financing the estimated $12.5 million cost of the new search, French Transport Minister Thierry Mariani said last month when announcing the new search. About $28 million has already been spent on the three previous searches for the jet's wreckage.
The search took on even more importance last week, when French judge Sylvie Zimmerman filed preliminary charges of manslaughter against both Air France and Airbus.
Without obtaining the flight data and voice recorders, experts say, the cause of the crash, and who should shoulder most of the blame, will likely never be known.
Under French law, preliminary charges mean the investigating magistrate has sufficient reason to suspect wrongdoing. The step allows the magistrate to continue investigating before determining whether to send the case to trial.
The cause of the crash remains unclear. Automatic messages sent by the Airbus 330 jet'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.
Air France CEO Pierre-Henri Gourgeon told reporters last week that the pitot problems were "a contributing factor but not the principal cause" of the crash. He defended his company, saying Air France had taken all necessary measures to fix faulty sensors.
Airbus knew since at least 2002 about the pitot problems, but air safety authorities did not order their replacement until after the crash.
The tubes, about the size of an 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 35,000 feet (10,600 meters).
In November, Air France issued a memo to investigators saying the carrier had counted 15 incidents in which the sensors had iced over on the same aircraft type in the 10 previous months before the crash.
The airline said it had informed Airbus and Thales about those findings, and estimated that about 16 documents that traced Air France's exchanges with Airbus showed that the planemaker didn't respond to its concerns.