The French nuclear submarine arrived off the coast of Brazil this morning to search for Air France flight 447's flight recorders.

The recorders, or black boxes, contain the vital clues as to what brought the Airbus A330 down and will only emit locating signals for another 20 days.

The sub, the Emeraude, which is equipped with high-tech sonar equipment, joins search teams from several countries in the race against time to find these flight recorders.

"Its mission is to detect the acoustic signals sent by the black boxes," French military spokesman Christophe Prazuck told ABC News. "It is capable on a daily basis of patrolling in a zone of 20 nautical by 20 nautical miles, 36 kilometers by 36 kilometers (22 miles by 22 miles), to detect acoustic signals sent by the black boxes."

"It will change zones every day," he said.

The Emeraude will work in conjunction with a research vessel from the French Research Institute for Exploitation of the Sea, the Pourquoi Pas, that carries underwater robots and is due to arrive in the region Friday.

The Pourquoi Pas is the only vessel in the French arsenal that carries suitable devices to retrieve and locate the black boxes, if their signals are ever detected.

"This special submarine is on board the Ifremer's sea research vessel Pourquoi Pas and is expected in the area Friday," Prazuck told ABC News.

In all, there are 400 French military personnel in the area.

Bodies Recovered

A total of 41 bodies have now been found in the Atlantic Ocean from Air France flight 447, the airline announced Tuesday evening.

And as divers continue to recover remains and wreckage from the crash site, airlines worldwide scramble to replace plane speed sensors on a number of Airbus jets.

Investigators looking into the accident believe speed sensors malfunctioned on the flight, and the problem could have caused the plane to fly at an unsafe speed.

Now Delta, US Airways and United, which flies a different model of Airbus, are rushing to finish replacing their sensors. Faulty speed readings can cause the jet to fly dangerously slow or fast.

It's not known for sure whether the sensors contributed to the crash 10 days ago, but pilots at Air France aren't taking chances. They've pressured the airline to quickly upgrade the speed sensors, called pitot tubes.

"We are really concerned," said Louis Jobard of Air France's pilots' union. "We have had some incidents, you know, before, reported on the Airbus 330 and Airbus 340 with the old type of pitot sensor."

The speed sensor changeover was recommended by Airbus 17 months ago, but it's common for airlines to take their time on work that is considered noncritical. Airbus had recommended changing the sensors because of reliability issues, and Air France had noticed sensors icing up on some flights.

The sensors had not yet been changed on flight 447, which former National Transportation Safety Board managing director Peter Goelz said was "not unusual."

"The recommendation that was made to Air France was not an emergency recommendation," Goelz said. "It was a recommendation that could be completed over time. And given the economics of the airline industry now, no air carrier wants to take their plane out of service unnecessarily."

In the Air France crash, pilots weren't just struggling with equipment problems: It was likely a series of failures and mishaps that led to the tragedy.

Among them, weather consultant Tim Vasquez has determined the plane's flight path would have taken the jet right through a series of towering thunderstorms.

Air France 447: Airline Safety Initiatives

The push to replace potentially faulty sensors is one of several efforts under way to make sure travelers are safe.

In separate initiatives, the Federal Aviation Administration called on investigators Tuesday to immediately focus on pilot training required by smaller, regional airlines in response to a deadly crash this winter in Buffalo, N.Y.

Also, the National Transportation Safety Board began a three-day hearing Tuesday into the rare success story of US Airways flight 1549, which landed on New York's Hudson River in January.

The bodies recovered from Air France flight 447 will soon be identified and examined for any injuries that may help explain what happened.

Despite the progress in the search, Goelz said it remains a daunting task.

"This issue with the wreckage is it's been at sea for at least six or seven days," he said. "They've got to chart currents, wind."

On Monday an "ocean of debris" surrounded divers recovering wreckage and bodies from the Atlantic Ocean, and searchers recovered the stabilizer from the plane's tail, according to the Brazilian Navy.

It's still unclear whether the jet broke up in the air or on impact. But former crash investigator Gregory Feith said they may be able to tell from the tail.

"If it's on the backside or the furthest up the debris chain, then there's a high probability that could have been one of the first components that came off the airplane," said Feith.

The evidence is being flown to the Brazilian island of Fernando de Noronha, some 400 miles off the country's coast.

The flight crashed with 228 people onboard en route from Rio de Janeiro to Paris after departing on May 31. As the hunt for clues picks up pace, searchers are scouring an area 45 miles from where plane last sent a burst of automated messages documenting failures in the flight's systems.

In the grim recovery effort, human remains will provide clues about what may have gone wrong.

Frank Ciaccio, who supervised wreckage recovery for Egypt Air and other underwater accidents while working for the NTSB, said full forensic examinations are "not going to solve all the answers," but can still provide crucial information.

"Identifying them is going to be the No. 1 priority," said Ciaccio, forensics specialist and vice president of commercial services for Kenyon International Disaster Management Services. "No. 2 priority is going to be to document any injuries the body sustains so that they can add to the investigation, and help with putting a final picture together."

"It's not going to solve why this plane went down, but it'll give something back to the family members that do find their loved ones right now, and it'll give some hope to the other ones that hopefully they will be able to recover more of their loved ones," he added.

ABC News' Zoe Magee, Ammu Kannampilly, Renata Araujo, Sonia Gallego, Joe Goldman, Christel Kucharz, Luis Martinez, Phoebe Natanson, Fabiola Antezana, Gabriel O'Rorke, Samira Parkinson-Smith, Kirit Radia and Christophe Schpoliansky, Reuters and The Associated Press contributed to this report.