RIO DE JANEIRO - A BURST of automatic messages sent by Air France Flight 447 offers few concrete clues into what made the plane crash into the Atlantic en route from Rio de Janeiro to Paris two weeks ago, an aviation expert said on Saturday.

The industry official, who has knowledge of the Air France investigation, told The Associated Press that a transcript of the messages posted on the website EuroCockpit is authentic but inconclusive.

Black boxes crucial UNLESS the plane's flight data and cockpit voice recorders - the so-called black boxes - are found, the exact cause of the accident may never be known. A French nuclear submarine is scouring the search area in the hopes of hearing audio pings from the black boxes' emergency beacons. The first of two U.S. locator listening devices won't arrive until Sunday. ... more

'There is a lot of information, but not many clues,' the official said, speaking on condition of anonymity because he is not authorised to discuss the matter.

The official said jets like the Airbus A330 that crashed automatically send such maintenance messages about once a minute during a plane's flight. They are used by the ground crew to make repairs once a plane lands.

Martine del Bono, spokeswoman for the French investigative agency BEA, which is in charge of the crash probe, and Airbus spokesman Stefan Schaffrath declined to comment on the transcript.

One of the 24 automatic messages sent from the plane minutes before it disappeared May 31 with 228 on board points to a problem in the 'rudder limiter,' a mechanism that limits how far the plane's rudder can move.

The nearly intact vertical stabiliser - which includes the rudder - was fished out of the water earlier this week by Brazilian searchers.

If the rudder were to move too far while travelling fast, it could shear off and take the vertical stabiliser with it, which some experts theorize may have happened based on the relatively limited damage to the stabiliser.

The industry official, however, said the error message pertaining to the rudder limiter did not indicate it malfunctioned, but rather that it had locked itself in place because of conflicting speed readings.

Investigators have focused on the possibility that external speed monitors - called Pitot tubes - iced over and gave false readings to the plane's computers.

'The message tells us that the rudder limiter was inoperative,' Jack Casey, an aviation safety consultant in Washington, D.C., said last week when the existence of the automatic messages was first divulged. 'It tells us that for some reason it was no longer functioning. That is all the message means.' 'It does not give you any reason why it is not working or what caused it, or what came afterward,' Mr Casey said. -- AP