The agency investigating the crash of Flight 447 said on Saturday that signals from the missing Air France jetliner suggest that its autopilot was not on before it vanished.

Paul-Louis Arslanian, the director of France's air safety investigation agency, said at a press conference in Paris that the plane sent 24 failure signals in the five minutes before contact was lost, suggesting that the aircraft experienced multiple systems failures before it plunged into the sea.

Arslanian said investigators are analyzing the 24 messages as they are still not sure whether the automatic pilot was shut off by the pilots or by the on-board computer because of the different data from the speed-measuring instruments.

He said some problems had been detected with the speed-measuring instruments on the Airbus A330 of which the manufacturer Airbus had recommended a replacement.

"There is a program of replacement, of improvement," he said, adding that planes that have not yet had the replacement are not necessarily dangerous, and that in other cases pilots had been able to regain control.

But he said the black boxes may have become detached from a beacon which sends out an ultrasonic signal.

Arslanian said earlier that the prospect of retrieving the black boxes were not good since they must have sunk to the bottom of the sea.

He said the ultra-sensitive detection equipment provided by the United States to help in the search for the airliner is to be transported on two ships to the search zone. Both ships are able to recover objects at depths of up to 6,000 meters.

Arslanian did not formally rule out the possibility that a terrorist bomb might have destroyed the plane.

French Defence Minister Herve Morin on Friday also said that the possibility of a terrorist attack on Air France Flight 447 cannot be ruled out.

The pilots aboard reported the plane was flying through an area of electrically charged cumulonimbus clouds before it vanished, causing early speculation as to the cause of the accident to be focused on foul weather, but Arslanian said the weather conditions had not been exceptional for the region.

The Air France Airbus A330 vanished over the Atlantic Ocean early on Monday after leaving Rio de Janeiro for Paris, with 228 people on board, including nine Chinese.

(Xinhua News Agency June 7, 2009)