LE BOURGET, France - French investigators on Thursday will present their initial findings into what caused Air France Flight 447 to drop out of the sky in the middle of the Atlantic a month ago, prompting one of history's most challenging plane crash investigations.
The Airbus A330-200 plane flying from Rio de Janeiro to Paris went down with 228 people on board in a remote area of the Atlantic, 930 miles (1,500 kilometers) off Brazil's mainland and far from radar coverage.
A burst of automated messages emitted by the plane before it fell gave rescuers only a vague location to begin their search, which has failed to locate the plane's black boxes. The chances of finding the flight recorders are falling as the signals they emit fade. Without them, the full causes of the tragic accident may never be known.
The French air accident investigation agency, the BEA, will present its preliminary report to journalists at its headquarters in Le Bourget, outside Paris.
Families of the victims are meeting with BEA and Air France officials at the French Transport Ministry just beforehand, according to Christophe Guillot-Noel, head of an association for victims of Air France Flight 447.
"The families are hoping to have all the facts, above all to be able to avoid this eventually happening again," he said.
"We have just one demand: transparency. We have just one expectation: the truth," he said.
Lacking the crucial evidence the black boxes contain, the BEA's initial findings will be based on the automated messages sent by the plane minutes before it lost contact, and clues from the wreckage and the remains of 51 people that have been recovered by investigators.
One of the automatic messages emitted by the Air France plane indicates it was receiving incorrect speed information from external monitoring instruments, which could destabilize the plane's control systems. Experts have suggested those external instruments might have iced over. Air France has now replaced the monitors, called Pitot tubes, on all its Airbus A330 and A340 aircraft.
Emergency beacons attached to cockpit voice and data recorders are built to emit strong "pings" for 30 days after a crash before fading away, though experts said they could continue for as long as 45 days.
The search for the Flight 447 black boxes is continuing even though the 30-day mark has past and there is no certainty they are still emitting signals. Brazil has ended the search for more bodies.
The black boxes - which are in reality bright orange - are resting somewhere on an underwater mountain range filled with crevasses and rough, uneven terrain.
The remote location, combined with the mystery of what happened to the plane - the pilots had either no time or no radio frequency to make a mayday call - makes the inquiry exceptionally challenging.
The families' association addressed a letter to the CEO of Air France, Pierre-Henri Gourgeon, demanding answers to several questions about the plane.
In the letter, published in Le Figaro on Thursday, the families ask for a detailed explanation of the flurry of automated messages sent by the plane before the crash; whether the messages arrived in chronological order or in order of importance; what procedures Air France has in place for planes entering storm zones; and how much freedom pilots have to change routes in case of menacing weather.
Investigators should have an easier time recovering debris and clues in the crash of a Yemeni Airbus 310 with 153 people on board that went down Tuesday just nine miles (14.5 kilometers) north of the Indian Ocean island-nation of Comoros.
Vandore reported from Paris. Associated Press writer Angela Charlton in Paris contributed to this report.
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