Airbus Said to Have Cited Sensor Concerns Before A330 Jet Crash

[1969pontiac]

June 6 (Bloomberg) -- Airbus SAS advised airlines more than a year ago to replace airspeed sensors on its A330 jet, the model that crashed into the Atlantic Ocean on an Air France flight to Paris, two people with knowledge of the matter said.

The service bulletin about the Thales SA parts was a recommendation, said the people, who asked not to be identified because the memo was confidential. Officials are said to be studying whether flawed data from ice-damaged sensors could have confused the flight computer or pilots on the June 1 flight.

“Recommendations are frequent and not issued in cases where there’s a truly pressing concern,” said Richard Aboulafia, vice president at consultant Teal Group in Fairfax, Virginia. In cases deemed critical, regulators put out binding directives.

Air France has been installing the new sensors, which are less vulnerable to ice, as the jets undergo scheduled overhauls, one of the people said. The people familiar with the advisory didn’t know whether the work had been done on the lost A330.

Accurate airspeed readings are pivotal because flying too fast can damage a plane’s airframe and traveling too slowly risks losing lift in a so-called aerodynamic stall. Flight 447 disappeared with 216 passengers and 12 crew members en route to Paris from Rio de Janeiro.

The only clues so far to what went wrong are the presence of violent turbulence and the “incoherence of the different speed measurements” transmitted from the jet, France’s BEA air- accident investigation bureau said on June 4.

‘Small Problems’

“Like any other aircraft, this plane had problems that were dealt with” during its four-year service history, although nothing obviously dangerous, BEA Director Paul-Louis Arslanian said on France 2 television. “One of our sources of information is the examination of all these small problems,” he said without elaborating.

Stefan Schaffrath, a spokesman for Toulouse, France-based Airbus, declined to comment on the planemaker’s service bulletins. Veronique Brachet, a spokeswoman for Paris-based Air France, declined to comment on the airspeed sensors, saying all information would be given to investigators.

Discrepancies among readings from the A330’s three airspeed sensors could have triggered the shutdown of the autopilot four minutes before the last message from the jet, or pilots may have taken control when they became concerned about that data or another problem, a person with knowledge of the probe said.

In an advisory about the crash sent to airlines on June 4, Airbus reminded pilots of the need to maintain engine thrust and the proper rate of climb when airspeed data become unreliable, as detailed in flight manuals.

Measuring Airspeed

The sensor on the A330 is a so-called Pitot tube, named after the French engineer who discovered in the early 1700s that the pressure of a gas or liquid through a tube could be used to determine velocity. According to Thales, its unit includes an electric heating system to “limit the risk of icing” that could obstruct the airflow and produce faulty readings.

Thales will be asked to supply information to crash investigators, the person with knowledge of the inquiry said. Christophe Robin, a spokesman for the Neuilly-sur-Seine, France- based company, didn’t immediately return a call to his mobile phone after regular business hours.

Blocked or damaged Pitot tubes have been blamed for air disasters including the 1996 crash of a Boeing Co. 757 flown by Alas Nacionales, which plunged into the Atlantic after takeoff from the Dominican Republic, killing all 189 people on board. Readings overstating the plane’s speed caused the pilots to fly too slowly and stall, investigators found.

Overshooting the Runway

In 1999, a blocked sensor contributed to the crash of a Boeing MD-11 flown by FedEx Corp. that overshot the runway as it attempted to land in the Philippines.

Brazilian and French search teams have yet to recover any confirmed debris from Flight 447, which was lost in an area without radar coverage.

In the jet’s last minutes, automated radio transmissions logged a catalog of failures, beginning with the disengagement of the autopilot and ending with a drastic drop in the pressure difference inside and outside the cabin, which can result from a plane’s disintegration or from a rapid decline in altitude.

According to the Airbus Web site, more than 600 A330s are in service around the world with 65 carriers, including Delta Air Lines Inc. and US Airways Group Inc. Both companies declined to comment.