RECIFE, Brazil (AP) -- A French nuclear submarine reached the crash zone of Air France Flight 447 on Wednesday to comb the Atlantic depths for black boxes that should help determine what brought the Airbus down in the sea off Brazil with 228 people on board.
The slow-moving attack sub Emeraude will be able to trawl patches of about 13 square miles (35 square kilometers) a day trying to pick up the boxes' acoustic beacons or "pingers," which are expected to start to fade 30 days after the May 31 crash, French armed forces spokesman Christophe Prazuck said Wednesday.
Brazilian searchers said they have now recovered 41 bodies from the scene. The remains are expected to be flown Wednesday to Recife, where investigators hope to identify them and find clues into the crash based on the victims' injuries.
Without key information from the Airbus 330's missing data recorders, investigators have focused on the possibility that external speed monitors - Pitot tubes - iced over and gave false readings to the plane's computers as it flew into thunderstorms.
Wreckage and the bodies were found about 400 miles (640 kilometers) northeast of the Fernando de Noronha islands off Brazil's northern coast.
Airlines around the world have begun replacing Pitot tubes on their aircraft. And the European Aviation Safety Agency, responsible for certification of Airbus planes, said Tuesday that it was "analyzing data with a view to issuing mandatory corrective action" following reports about the possible malfunctioning of the Pitot tubes.
It said this action should not prejudge the outcome of the investigation into the Air France crash and that the causes of the accident are still unknown.And it said the A330 and other Airbus aircraft are safe to operate.
It issued a safety information bulletin on Tuesday as a precautionary measure reminding operators of the correct procedure if speed indications are unreliable or missing.
An important part of the investigation relies on a burst of 24 automatic messages the plane sent during the last minutes of the flight. The signals showed the plane's autopilot was not on, officials said, but it was not clear if the autopilot had been switched off by the pilots or had stopped working due to conflicting airspeed readings.
The L-shaped metal Pitot tubes jut from the wing or fuselage of a plane, and are usually heated to prevent icing. The pressure of air entering the tubes lets internal sensors measure the speed and angle of flight. A malfunctioning tube could mislead computers controlling the plane to dangerously accelerate or decelerate.
Air France said it began replacing the tubes on its A330 and A340 jets in May after pilots reported several incidents of icing leading to a loss of airspeed data, and that it had already replaced the Pitots in smaller A320 jets after similar problems were reported.
"What we know is that other planes that have experienced incorrect airspeed indications have had the same Pitots. And airplanes with the new Pitot tubes have never had such problems," said Air France pilot Eric Derivry, a spokesman for the SNPL pilots union.
While no cause has been established for the disaster, Derivry said the Pitot failures create "a web of presumptions, but only presumptions," that they could be a contributing factor.
On Tuesday, the airline assured its pilots that none of its A330s or A340s would fly without at least two of the new instruments, and that all Air France A330s and A340s will have all three Pitots replaced by July. Brazil's air force said it is replacing them for the president's jet.
But some pilots said the planes should remain flyable even if Pitot tubes ice over in thunderstorms. And the European Aviation Safety Agency issued a precautionary safety bulletin Tuesday reminding operators about existing procedures to fly the aircraft safely even when air speed indicators malfunction.
"We are aware of issues with this in the past, but at no time were they classified as safety-critical," said Daniel Hoeltgen, the agency's spokesman.
About 70 airlines operate some 600 A330 planes similar to the doomed Air France jet, and two companies manufacture the Pitot monitors for them: France's Thales Group and Charlotte, North Carolina-based Goodrich Corp.
Thales made the Pitot tubes on the plane that crashed, company spokeswoman Caroline Philips confirmed. She did not say how many other planes use the devices.
Marco Sibaja reported from Recife and Greg Keller from Paris. Associated Press writers contributing to this report included Federico Escher in Fernando de Noronha, Brazil; Alan Clendenning in Sao Paulo; Emma Vandore in Paris; David Rising in Berlin; Slobodan Lekic in Brussels; Eileen Ng in Kuala Lumpur; Adam Schreck in Dubai, United Arab Emirates; Harry Weber in Atlanta and Cecile Brisson in Paris.