Air France says it's replacing flight instruments

Plan detailed in memo sent to its pilots

Tuane Rocha, fiancee of a passenger aboard the ill-fated Air France Flight 447, cried during a Mass at Our Lady of Carmo Cathedral yesterday in Rio de Janeiro. Tuane Rocha, fiancee of a passenger aboard the ill-fated Air France Flight 447, cried during a Mass at Our Lady of Carmo Cathedral yesterday in Rio de Janeiro. (Antonio Scorza/AFP/Getty Images)
By Marco Sibaja and Greg Keller
Associated Press / June 6, 2009
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RECIFE, Brazil - An Air France memo to its pilots yesterday about the crash of Flight 447 said the airline is replacing instruments that help measure air speed on all its medium- and long-haul Airbus jets.

Investigators have focused on incorrect speed readings as a potential factor in the crash.

With Brazil and France disagreeing about whether pieces of the jet have even been found in the Atlantic, investigators are using the last messages sent by the plane to determine the cause and try to avoid future disasters.

Air France declined to comment on the memo obtained by the Associated Press, saying it was for pilots only.

Airbus said the matter was part of the investigation into the crash that killed 228 people flying from Rio de Janeiro to Paris on Sunday. The Bureau of Investigation and Analysis, which is leading the French investigation of the crash, said it would address all questions at a news conference today.

The memo sent yesterday said Air France has been replacing instruments known as Pitot tubes and will finish in "coming weeks." It does not say when the replacement process started.

The plane's "black boxes" may be miles below the surface and investigators are looking for clues in the messages sent from the plane's computers just before it disappeared. One theory: The outside probes that feed speed sensors may have iced over, giving incorrect information to the plane's computers. The autopilot may have then directed the plane to fly too fast or too slow when it met turbulence from towering thunderstorms.

Airbus sent an advisory to airlines late Thursday reminding them how to handle the A330 in similar conditions.

The memo sent by Air France yesterday says that a series of actions to reduce the risks of loss of airspeed information are being reinforced by "notably, the improvement of Pitot models on Airbus' fleet of medium- and long-haul flights."

"On this topic, a program of replacing Pitots with new models is underway," the memo reads. "It should be completed in coming weeks."

Pitot tubes are L-shaped metal tubes - about 8 inches long on their longer side - that protrude from the wing or fuselage of a plane. The pressure of the air entering the tube lets sensors measure the speed and angle of the flight, along with less vital information such as outside air temperature.

They are heated to prevent icing.

A blocked or malfunctioning Pitot tube could cause an air speed sensor to work incorrectly and cause the computer controlling the plane to accelerate or decelerate in a potentially dangerous fashion.

Airbus said the French agency investigating the crash found that the doomed flight had faced turbulent weather and inconsistency in the speed readings by different instruments.

That meant "the measured air speed of the aircraft was unclear," Justin Dubon said.

In such circumstances, flight crews should maintain thrust and pitch and - if necessary - level off the plane and start trouble-shooting, Dubon said.

Meteorologists said the Air France jet entered an unusual storm with 100-mile-per-hour updrafts that acted as a vacuum, sucking water up from the ocean. The moist air rushed up to the plane's high altitude, where it quickly froze in minus-40 degree temperatures. The updrafts also would have created dangerous turbulence.

The jetliner's computer systems ultimately failed, and the plane probably broke apart in midair.

Brazilian officials have insisted for three days that military pilots have spotted wreckage from Flight 447 scattered across the ocean's surface. But ships guided by planes in the search area have been hampered by extremely poor visibility, and have recovered no wreckage. "We don't have any information yet that any of the ships are near any of the objects," Cardoso said.