PARIS France's air crash authority will publish an interim report in December on the possible causes of a fatal crash by an Air France plane, it said on Monday.
Flight AF447, an Airbus A330, plunged into the Atlantic ocean, en route from Rio de Janeiro to Paris, on June 1, killing 228 people. The causes of the accident and its exact location remain unknown.
"At this stage, we do not have any factors which allow us to say what happened in the cockpit," said Jean-Paul Troadec, the new head of France's air crash investigation board, BEA.
"Our current knowledge of the accident does not allow us to put together a scenario," he told a news conference.
The report will give details on the meteorological conditions on the day of the crash as well as the automatic messages sent by the plane's computers.
Marine searches will start at the accident site at the beginning of next year, once the budget and technical demands of the investigation are determined, Troadec said.
So far authorities have been screening from the air an expanse of ocean the size of Switzerland in a bid to find voice and data recorders and the bulk of the plane, which plummeted some 30,000 feet (9,000 metres) in four minutes in an equatorial storm.
The United States, Brazil, Britain, Germany and Russia are likely to take part in the investigation, whose cost is estimated at between 10 million and 20 million euros (9-18 million pounds), Troadec said.
Troadec declined to draw any conclusions on the exact causes of the accident. Some experts have suggested problems with the plane's speed sensors.
(Reporting by Matthias Blamont; writing by Sophie Taylor; editing by Robin Pomeroy)