The tail section of an Air France plane which crashed over the Atlantic in 2009 has been found on the ocean floor, relatives of those killed have said. Investigators had told them the section was "relatively intact", they added. The discovery has raised hopes that the "black boxes", which were located at the rear of the jet, may be recovered. The voice and data recorders could yield crucial clues about the cause of the crash that killed 228 people on the flight from Rio de Janeiro to Paris. There has been speculation that malfunctioning speed sensors were to blame, but officials say other factors must also have contributed. Nelson Marinho of the Brazilian victims' family association said French Accident Investigation Bureau (BEA) officials had told them during a meeting in Paris on Monday that the "tail section had been found and that it was relatively intact so the black boxes are possibly still attached to it" "I am 99% certain the black boxes will be recovered," he said. BEA spokeswoman Martine Del Bono urged caution about the news. "We are working intensely under a very short time span to have a maximum amount of information to able to find the black boxes," she said. "But we don't know where they are right now - we have to find them at the site." Maarten Van Sluys, another member of the Brazilian victims' family association, said there was also concern about the condition of the black boxes after two years sitting in corrosive seawater under immense pressure, nearly 4km (2.5 miles) below the surface of the ocean. "They made it clear that they could not guarantee that the content of the black boxes would be able to be retrieved," he told the Associated Press. Flight 447 crashed into the Atlantic north-east of Brazil on 1 June 2009, after running into an intense high-altitude thunderstorm. Automatic messages sent by the Airbus 330's computers showed it was receiving false air-speed readings from its sensors. The French transport ministry has said that the ship Ile de Sein, which is equipped with a remotely-operated submarine, will leave Cape Verde on 21 April to begin retrieving parts of the wreckage. The bodies of many of the victims were also found at the site.