LE BOURGET, France — A new euro10 million ($13.73 million) international search for the remains of Air France Flight 447 will begin in mid-March, nearly nine months after the passenger jet crashed in the Atlantic depths, France's chief air accident investigator said Wednesday.

The search plan, involving U.S. and Norwegian ships, covers some 770 square miles (2,000 square kilometers) of sea, said Jean-Paul Troadec, chief of the BEA investigation agency. He said the approximately four-week search is the most expensive and biggest operation his agency has ever conducted and "one of the most complex undersea operations ever."

Troadec said the first search efforts after the June 1 crash, which killed 228 people, "were not fruitful." Since then, "the investigation has stalled," he said, without further information from the crash site, including from the black box flight recorders that would provide crucial information on what went wrong. The black boxes have not been found.

"I think we have good chances" to find the black boxes, he said, a "largely above 50 percent" chance. But it will be tough, he added. "First we have to find the haystack, then we look for the needle."

The BEA chief initially said the search would begin within days, then clarified to say it would begin in mid-March, depending on weather, and materials would be put in place within days.

Families of victims of Air France Flight 447 have welcomed the new search effort.

John Clemes, whose brother was among the fatalities in the June 1 crash of the plane en route from Rio de Janeiro to Paris, says the search plan has "raised our hopes." It was shared with the families Wednesday before the BEA presented it at a news conference.

"Our one regret is that it took so long" to resume searching that was halted last summer, Clemes told The Associated Press.

Troadec said the search site includes depths of up to 4,000 meters (13,120 feet).

The new search will be jointly financed by Airbus and Air France. The U.S. Navy and the National Transportation Safety Board will help, along with accident experts from Britain, Germany, Russia and Brazil and private companies.

The lifespan of the so-called "pingers" attached to the black boxes is only about a month, but officials say submarines and boats equipped with sonar gear can find the wreckage from the Airbus 330 even without such signals.

Investigators "said the black boxes can survive that kind of an impact and that time under water," Clemes said.

The second and most recent search for the black boxes ended in August.

Investigators have insisted that the crash was likely caused by a series of failures, but that they won't know definitively without the black boxes.