Authorities investigating what caused Air France Flight 477 to crash into the Atlantic Ocean are looking at whether speed data instruments malfunctioned, say two officials.
The officials, who have knowledge of the investigation, said a bad speed sensor or an iced-over external probe may have given inaccurate data to computers controlling the jet.
The officials spoke with AP Thursday on the condition of anonymity because they weren't authorized to discuss the investigation.
Aviation analyst Bill Voss said if the jetliner was going too fast through heavy turbulence, it could break apart. If it was going too slow, it could stall.
A Brazilian helicopter crew pulled the first wreckage of Air France Flight 447 from the sea on Thursday.
Authorities have not discovered any sign of human remains, and Air France has told families that the plane broke in half, killing all 228 passengers.
The helicopter crew, which was working off a Brazilian navy ship, recovered a cargo pallet and two buoys -- standard emergency equipment on planes -- from the Atlantic Ocean about 550 kilometres northeast of the Fernando de Noronha islands.
Air France told family members at a private meeting that the Airbus A330 disintegrated, either in the air or when it hit the ocean, killing everyone on board.
A Canadian businessman was among those on the plane.
The accident is the deadliest crash in Air France history and the world's worst since 2001.
Crews have still been unable to retrieve the crucial black box voice and data recorders, which can operate 20,000 feet underwater.
The signal from the devices could be hampered by water temperatures or blocked by mountainous ocean ridges.
In the meantime, investigators are relying heavily on the plane's automated messages to help reconstruct what transpired as the jetliner flew through towering thunderstorms.
The messages show a series of failures, ending with its systems shutting down.
The jetliner disappeared after leaving Rio de Janeiro for Paris on Sunday night.
The pilot of Flight 477 sent a manual signal at 11 p.m. local time Sunday saying he was flying through an area of black, electrically charged cumulonimbus clouds.
At 11:10 p.m., an alarm sounded indicating controls needed to keep the plane stable had been damaged.
Three minutes after that, systems for monitoring, altitude, air speed and direction failed, along with the main flight computer and wing spoilers.
The last automatic message, at 11:14 p.m., signalled complete electrical failure and a loss of cabin pressure.
An aviation official who wished to remain anonymous told AP that the final signal suggests that the plane may have broken apart in the sky.
Ken Reeves, director of forecasting operations with AccuWeather, a commercial weather forecasting service in the U.S., said the storm may have not looked severe as the plane was approaching it, but may have increased in intensity shortly after Flight 477 entered into it.
As the storm worsened, the plane could have been experiencing upward gusts of about 160 kilometres an hour, he said.
"That kind of vibration ... of the plane certainly can cause problems in terms of handling and perhaps even damage," he told Â鶹´«Ã½net Thursday.
Thunderstorms pose the "greatest risk" to pilots because of the speed at which they can develop, he said, especially in the area that Flight 477 went down.
"Planes flying from South American to Europe encounter this all the time, and pilots will tell you that it's a very risky area to go through. So really it's up to the pilot and planning to try to avoid these types of areas as best as possible."
Most times, pilots try to maneuver around storms, but sometimes it isn't feasible to do so, he said.
Since planes travel at about 800 kilometeres or more an hour, they have to plan their moves far in advance, he said, adding that sometimes pilots can find themselves in situation in which the weather is changing too fast for them to react.
France's accident investigation agency has reported only two findings, one is that the automatic messages sent from Flight 447 gave conflicting signals about the plane's speed; the other is that the plane went through dangerous thunderstorms.
The agency warned against the speculation that the Air France plane was flying at the wrong speed.
Seas were calm Thursday as ships searched three debris sites to recover wreckage, but "extreme cloudiness" prevented U.S. satellites from helping, French military spokesman Christophe Prazuck told AP.
A U.S. navy P-3C Orion surveillance plane joined French and Brazilian planes air force to search an area of 6,000 square kilometres, Brazilian air force Gen. Ramon Borges Cardoso told AP.
So far, officials have spotted a seven-metre chunk of plane, an airline seat, an oil slick and several large brown and yellow pieces that possibly came from the plane's interior, Cardoso said.
Prazuck said the Pourquoi Pas, a French sea research vessel carrying manned and unmanned submarines, will be in the search zone by June 12 to assist in the search.
France is co-ordinating the accident investigation, and has invited the U.S. National Transportation Safety Board to help.
The U.S. team includes representatives from General Electric Aviation of Cincinnati, Ohio, maker of plane's engines, and Honeywell International Inc. of Morristown, N.J., maker of the plans communications and navigation systems.
As the search continues, so does the mourning. More than 500 people gathered in a historic Candelaria church in Rio de Janeiro Thursday for a mass for the victims of crash.
With files from the Associated Press
