An investigation of the crash of Air France Flight 447 is eying the possibility that defective airspeed sensors gave false readings to the plane's computers, but officials say it will be a while before the cause of the mishap is known.

Function of airspeed senspors

The external airspeed sensors, known as Pitot tubes, are pressure measurement instruments that detect the speed and angle of a plane's flight through the pressure of air entering the tubes.

The L-shaped metal sensors jut from the wing or fuselage of a plane and are heated to prevent icing.

The cause of Flight 447's plunge into the Atlantic as it flew from Rio de Janeiro to Paris with 228 people aboard remains unclear. But one theory is that the sensors became iced over and gave incorrect readings that could have caused the Airbus A330 to fly too slow or too fast.

Air France faces criticism

Scores of messages sent automatically by the plane before it disappeared showed conflicting speed readings. Some experts therefore speculated that the pilots failed to manage the correct speed and that led to the crash.

Paul-Louis Arslanian, the head of the French Investigation and Analysis Bureau, however, said earlier this month that Airbus had recommended that Air France replace its Pitot tubes because of previous malfunction reports but the airline didn't take the advice.

Air France clarified later, though, that it ordered replacement sensors on April 27 after pilots noticed a loss of airspeed data. The new sensors arrived three days before Flight 447 went down.

Air France chief executive Pierre-Henri Gourgeon told reporters on Thursday that the company will accelerate the replacement of the airspeed sensors on Airbus A330 and A340 models, but stressed: "I am not convinced that speed sensors were the cause of the crash."

Real cause remain unclear

Just what brought down the Air France jet remains a mystery. Aviation organizations and investigators keep an prudent attitude as they go about their work.

A plane crash is usually a combination of various factors, Gourgeon told French TV 2 in a interview Thursday.

"There is as yet no link between the pitot and the causes of the accident," a BEA spokeswoman said the same day.

Airbus declared earlier that all on-duty A330 planes are safe, including those with the older air speed monitors. On Friday, Airbus head Thomas Enders publicly defended the A330 jet for the first time.

"The A330 is one of the best and safest planes ever built," Enders told the German daily Bild Zeitung. "An Airbus plane takes off every two seconds somewhere in the world. Air travel is and will remain the safest means of transport."

He also warned that people should not speculate on the cause of the crash at a early state, as the investigation may take months.

"We need to be patient now. Investigations take time," Enders told the German newspaper. After such a catstrophe, the slightest information makes headlines."

Officials say the cause of the crash won't be conclusively determined until the plane's black boxes - the best hope of definitively learning what went wrong are recovered.

The French nuclear submarine Emeraude is now scouring 35 square kilometers of ocean bottom in the hopes of hearing pings from the boxes' emergency beacons. US military locating equipment capable of picking up signals 6,100 meters deep won't arrive until Sunday.

Searchers so far have recovered the bodies of 44 victims near Fernando de Noronha archipelago off Brazil's northern coast. Sixteen of the bodies have been taken to Brazil for identification and more are to follow, officials said.

(Xinhua News Agency June 13, 2009)