A slick believed to be from the fuel of Air France Flight 447 is seen from the window of a Brazilian air force plane patrolling the crash area in the Atlantic Ocean roughly 1,200 kilometres northeast of Recife. (Brazilian air force/Reuters)

Investigators are going to resume the search for the wreckage and black boxes of Air France Flight 447, which crashed last June in stormy weather, killing 228 people on board.

"I think we have good chances" to find the black boxes, said Jean-Paul Troadec, chief of the BEA investigation agency on Wednesday. "Largely above 50 per cent" chance, but it will be difficult, he said.

"First we have to find the haystack, then we look for the needle."

The four-week search, involving U.S. and Norwegian ships, will cover 2,000 square kilometres of sea, he said.

Troadec said the investigation has stalled since the crash.

The Air France Airbus A330 was en route from Rio de Janeiro to Paris when it disappeared from radar screens.

The crash was the world's deadliest commercial airline disaster since Nov. 12, 2001, when an American Airlines jetliner crashed in the New York City borough of Queens during a flight to the Dominican Republic, killing 265 people.

The cause of the crash has not yet been determined. Some officials have speculated the plane may have been struck by lightning, but aviation experts have said that should not have been enough to bring down the aircraft.

Other potential causes include shifting winds and hail from towering thunderheads, a massive mechanical failure or a combination of other factors.

With files from The Associated Press