Paris, France (CNN) -- Investigators seeking the cause of the mysterious crash of an Air France jet last year have significantly narrowed the area they are searching to find the wreckage, a top official said.
Air France Flight 447 crashed into deep Atlantic waters on June 1, killing all 228 people aboard. Most of the bodies -- and the flight's data recorders -- have never been recovered, despite extensive searches of the ocean floor.
But the French air accident investigation agency, the BEA, is still hopeful, its head, Jean-Paul Troadec, told CNN on Wednesday.
"We have determined a much smaller area which is about one-tenth of the previous area" being searched, he said.
Investigators still do not know what brought down the plane, who was at the controls when it crashed, or what the pilots did in the moments leading up to the disaster, according to their latest report, released in December.
But if they can locate the flight data recorder and the cockpit voice recorder, they should be able to determine the circumstances "very quickly, some weeks after the readout of the recorders," Troadec said Wednesday.
The problem is that the plane went down in extremely deep water with enormous underwater mountains.
"The area is very badly known," Troadec said, adding that ocean currents have not been mapped in the region, making it "difficult to analyze the trajectory of the debris.
"We are in the middle of nowhere," he said.
Two vessels, one American and one Norwegian, will trawl about 2,000 square kilometers in the latest phase of the search, which will last four weeks, he said. That's down from about 17,000 square kilometers in the initial hunt last year.
"So, of course, it's much more easy to try to find the recorders," he said.
Troadec said his agency is determined to press on with the hunt, even as the investigation threatens to become the most expensive in air accident history.
"We have to perform this new phase because it's the only chance we have to explain this accident," he said.
Patricia Coakley, whose husband, Arthur, died in the crash, said she doesn't need to know the cause of the disaster.
"It was an accident. No matter what, it's not going to help me. ... Because it's not going to bring him back, is it?" she said.
Flight 447 -- an Airbus A330 -- went down in stormy weather in the Atlantic Ocean while flying from Rio de Janeiro, Brazil, to Charles de Gaulle Airport in Paris, France.
Some debris and bodies have been recovered, and an examination shows the plane hit the water belly first, essentially intact, officials have said.
Automated messages sent from the plane in the minutes before the crash showed there were problems measuring airspeed, the investigators said in December. But that alone was not enough to cause the disaster, they added.
Tests have already brought into question the performance of pitot tubes, which measure the pressure exerted on the plane as it flies through the air, and are part of a system used to determine air speed.
Before it crashed, Flight 447 sent out 24 automated error messages that suggested the plane may have been flying too fast or too slow through thunderstorms, officials have said.
The European Aviation Safety Agency issued a directive in late August requiring airlines to replace pitot tubes manufactured by Thales Avionics on Airbus A330s and A340s. It said airlines should replace them with other Thales tubes and those manufactured by Goodrich.
CNN's Claire Boube, Niki Cook and Don Riddell contributed to this report.