Pilots question airspeed sensors’ troubled history

Pitot speed sensors, manufactured by North Carolina-based Goodrich Corp., are seen on a Boeing 747 displayed at the Air and Space Museum in Le Bourget, north of Paris. Despite documented problems with the type of speed sensors on its planes since at least 2002, Airbus did not replace the equipment until after a crash in June that killed 228 people, the Associated Press has found.

? Airbus knew since at least 2002 about problems with the type of speed sensor that malfunctioned on an Air France passenger plane that went down in June, The Associated Press has learned. But air safety authorities did not order their replacement until after the crash, which killed all 228 people aboard.

The tubes, about the size of an adult hand and fitted to the underbelly of a plane, are vulnerable to blockage from water and icing. Experts have suggested that Flight 447’s sensors, made by French company Thales SA, may have iced over and sent false speed information to the computers as the plane ran into a thunderstorm at about 35,000 feet.

The exact role the sensors — known as Pitots — played in the crash may never be known without the flight recorders, which have not been recovered and which have stopped emitting signals. Investigators insist sensor malfunction was not the cause of the crash, but many pilots think false speed readings may have triggered a chain of events that doomed the plane.

Fernando Alonso, head of Flight Operations at Airbus, maintains the doomed Airbus A330 plane was “totally airworthy.”

The plane was flying from Rio de Janeiro back to the French capital when it went down in a remote area of the Atlantic, 930 miles off Brazil’s mainland and far from radar coverage. Automatic messages transmitted by the plane show its computer systems no longer knew its speed, and the automatic pilot and thrust functions were turned off.

Several European airline pilots, including former Air France captain Gerard Feldzer, believe a reading of the messages suggests Air France pilots were suddenly forced to take manual control in near impossible conditions: a cockpit ringing with warning bells and flashing lights, some of them contradictory, with few clues to speed, altitude and nighttime weather conditions.

“It’s very difficult when you are already experiencing turbulence in the middle of the night, to know what to do,” said Feldzer, adding that the plane’s automated warning system could have been issuing incorrect instructions. “It’s very difficult to resist what you are being ordered to do because they are false orders.”

Air France is now starting a training program for pilots on how to manage a Pitot malfunction at high altitudes of the type experienced on Flight 447. Previously, Air France had only offered simulator training for Pitot malfunction on take-off and landing.

Pilots are angry about what they see as an attempt to pin the crash on pilot error. Eric Tahon, an Air France pilot, defended the role of the Flight 447 crew.

“We are trained to deal with multiple failures of the plane,” he said. “We are convinced that without the breakdown of the Pitots, Air France 447 that day would have set down at (Paris’) Roissy (airport).”

Feldzer, however, said that while the dangers now appear to have been underestimated, he believes Airbus and Air France would not have risked their reputations had they thought Pitot faults were critical.

A series of industry documents verified by investigators show that regular warnings on Airbus Pitots popped up as far back as 1994, although for a different model that was later banned in 2001 by French aviation officials.

An Airbus memo from July 2002 warns of blocked drainage holes on the Thales AA Pitot — the type fitted onto the doomed Air France jet.

Airbus recommended replacing Thales Pitots with a newer model in 2007 but did not make the change mandatory. And Air France decided to replace Pitots on its longer range Airbus fleet only when they broke down.

Air France says it started having problems with speed-measuring equipment on long-range Air France A330 and A340 jets in May 2008, which Airbus blamed on ice crystals blocking Pitot tubes. But functioning sensors were not replaced at that stage.