Problems Found in Airspeed Sensors on Airbus A330 Planes

8.8.2009   (New York Times)


Washington.   A component suspected of playing a role in the crash of Air France
447 over the Atlantic Ocean on June 1 has also malfunctioned on at least a dozen
Northwest Airlines flights, federal investigators have discovered.

 The part helps a plane measure its airspeed. The discovery suggests the equipment
problems on planes are more widespread than previously believed. It also gives
new urgency to airlines already scrambling to replace the part, an air sensor,
and figure out how the errors went undetected despite safety systems.

The equipment failures, all involving Northwest Airlines Airbus A330s, were brief and were noticed only after safety officials began investigating
the Air France crash on a Rio de Janeiro to Paris flight and two other recent
in-flight malfunctions.  The failures were described by people with knowledge
of the investigation who spoke only on condition of anonymity because they were
not authorized to comment publicly.

Human pilots and automatic systems require accurate air speed data to keep the
plane flying.

Automatic messages from the plane indicated problems with airspeed readings.
French investigators have focused on the possibility that Flight 447’s sensors
iced over and sent false speed information to the computers as the plane ran into
an area of storms at about 35,000 feet.

Three weeks after the Air France crash, the National Transportation Safety Board announced that it was investigating two other A330 flights that experienced
a loss of airspeed data.

The most recent problem was on June 23, when a Northwest flight hit rain and
turbulence while on autopilot outside of Kagoshima, Japan.   According to an N.T.S.B.
report, speed data began to fluctuate.   The plane alerted pilots it was going
too fast.   Autopilot and other systems began shutting down, putting nearly all
the plane’s control in the hands of the pilot, something that usually happens
only in emergencies.

In May, a plane belonging to a Brazilian company, TAM Airlines, lost airspeed
and altitude data while flying from Miami to São Paulo, Brazil.   Autopilot and
automatic power also shut down and the pilot took over, according to an N.T.S.B.
report.   The computer systems came back about five minutes later.

"These two cases we know were dealt with effectively by the crew, and we think
this happened in Air France and maybe wasn’t dealt with effectively," said Bill
Voss, president of the Flight Safety Foundation, an aviation safety research group.

Like the Air France flight, the newly discovered Northwest cases and the two
other malfunctions under investigation involved planes with sensors made by the
European company Thales.