Search crews in the Atlantic struggled on Friday to recover wreckage from an Air France flight as hopes dwindled of finding bodies from a crash possibly caused by pilots acting on flawed speed readings.

The Associated Press reported Air France was replacing equipment that affects flight speed in some of its jets. An Air France spokesman told Reuters the company would not comment on internal information aimed at pilots.

Before it crashed, the aircraft sent a series of automated messages that contained inconsistencies in the airspeed measurements, according to investigators.

Air France said in a memo to pilots that in coming weeks it will replace instruments known as Pitot tubes that help measure air speed and angle of the flight, according to the AP. The memo did not say when the replacement process began, the AP said.

Airbus, maker of the A330 jet that crashed on Monday killing all 228 people on board, issued a warning late on Thursday that pilots should follow standard procedures -- to maintain flight speed and angle -- if they suspect speed indicators are faulty.

Airbus said its message to clients did not imply pilot error or that a design fault caused the crash of Flight AF 447, the world's deadliest air disaster since 2001 and the worst in Air France's 75-year history.

This Aircraft Information Telex is an information document that in no way implicates any blame, Justin Dubon, a spokesman for Airbus, said on Friday.

More than 300 aircraft similar to the Air France jet -- an Airbus A330-200 -- are in service worldwide.

INITIAL REPORT BY END OF MONTH

The French air accident investigation agency aims to release an initial report by the end of the month. But finding the evidence contained in debris and, crucially, in black box flight recorders is proving a monumental task.

France has sent a nuclear-powered submarine with advanced sonar equipment to help locate the black box and sunken debris, armed forces spokesman Christophe Prazuck said. But he added the black box may not be emitting the signal that identifies its position.

We have to take this chance and give it a go, but it's a long shot. We need some luck, he said.

The slim chances of finding bodies in the shark-infested waters led searchers to focus on gathering debris, but by Friday it was becoming increasingly difficult to do that.

The wreckage spotted by Brazilian air force planes is spread over a huge area of ocean about 1,100 km (680 miles) off the country's northeastern coast, and earlier concentrations of debris are breaking up.

We had an area of approximately 5 kilometers (1.9 sq miles) of materials, but the current has dislocated it, Air Force Brigadier Ramon Borges Cardoso said.

Teams had earlier pulled out a wooden pallet that appeared to be part of the plane, but later said it was marine trash.

Searchers believe a large part of the plane may have sunk along with its occupants if it was relatively intact when it hit the ocean, military sources said.

FINAL MESSAGES

French magistrates have opened an investigation into possible manslaughter over the crash, the prosecutor's office said on Friday, a routine procedure after such a large loss of life and which could take years to complete.

Investigators know from the aircraft's final batch of automated messages, which were sent over a three-minute period, that there was an inconsistency between the different measured airspeeds shortly after the plane entered a storm zone.

An industry official said warnings such as the one Airbus sent on Thursday are only issued if accident investigators have established facts that they consider important enough to pass on immediately to airlines.

The recommendation was authorized by the agency looking into the disaster, which has said the speed levels registered by the slew of messages from the plane showed incoherence.

An aviation expert, who declined to be named, said the plane's airspeed sensors, called pitot tubes, work on air pressure and might provide incorrect readings if they get obstructed by objects such as ice.

The tubes are heated to prevent icing at high altitude and there was no immediate information on what went wrong.

Airbus said the correct procedure when confronted by unreliable speed indications was to maintain thrust and pitch and start trouble-shooting.

The Airbus telex has revived a long-standing debate among pilots over whether the Airbus planes are overly complex.

This is a plane that is conceived by engineers for engineers and not always for pilots, Jean-Pierre Albran, a veteran pilot of Boeing 747s, told Le Parisien newspaper.