Yielding answers: The flight recorders of Air France flight 447, which crashed in 2009. The recently recovered 'black boxes' are delivering long-awaited answers into the disaster. Picture: Michel Euler Source: AP

An Air France plane crashed into the ocean after a sudden stall, according to one of the investigation team.

Investigators said over the weekend, they would announce initial official findings from their probe later this week.

Spiegel magazine, quoting an unnamed expert who has been analysing data from the recently recovered flight recorders, said the exact causes of the crash were not known, but data suggested the plane's speed probes, known as pitot tubes, iced up, resulting in the Airbus A330's failure to register correct airspeed.

The 2009 accident, which resulted in the death of all 228 people aboard the plane, happened over just four minutes, according to data from the flight recorders recovered last month from the bottom of the Atlantic Ocean.

According to the voice recorder, chief pilot Marc Dubois was not in the cockpit when an initial alarm rang out.

He is heard running into the cockpit and "shouting instructions to his two co-pilots", the expert told Spiegel.

The plane, en route from Rio de Janeiro to Paris on June 1, 2009, appeared to have avoided an area of strong turbulence, but its pitot tubes gathered ice particles from the weather front.

Then "the data recorder indicates an abrupt heaving of the machine shortly after airspeed indicators failed", the expert said.

This resulted in the plane's deep stall.

It was not clear if this was the result of pilot error, or if onboard computers had automatically kicked in to compensate for what appeared to be a sudden loss of power, the magazine said.

The case has been closely followed in Germany because 28 of the passengers were German.