Says Computer Fault Led To Wild Ride

Australia's Transport Safety Bureau says it knows why an Airbus A330-300 dropped about 650 feet within seconds over Western Australia last week. Investigators have pinpointed the cause of the incident to a fault in the aircraft's flight data computer, which shut off the plane's autopilot.

As ANN reported, dozens of passengers were injured when the aircraft violently lurched during an October 7 flight from Singapore to Perth, falling several hundred feet from its 37,000-foot cruising altitude. Speculation initially pointed to clear air turbulence, but days later Qantas curiously pointed a finger at potential electronic interference from a passenger's laptop computer.

It now appears both hypotheses were in error. Bloomberg reports Airbus SAS immediately issued an alert Tuesday after the ATSB issued its preliminary report, advising operators of the advanced widebody airliner -- and its larger A340 sibling -- to be aware of an apparent glitch in air data computers manufactured by Litton Industries, a subsidiary of Northrop Grumman.

"This appears to be a unique event," the ATSB noted in its report, adding the advisory issued by Airbus is "aimed at minimizing the risk in the unlikely event of a similar occurrence."

The ATSB says its preliminary analysis determined one of the A330's three Air Data Inertial Reference Unit sent incorrect information to the aircraft's fly-by-wire flight control system, which caused the autopilot to disconnect due to warnings of an imminent stall. The jet dropped when the air data unit triggered "a nose-down aircraft movement, which resulted in the aircraft pitching down to a maximum of about 8.5 degrees."

The Board added the ADIRU "generated very high, random and incorrect values for the aircraft's angle of attack," and triggered repeated stall and speed warnings over a two-minute period following the incident. By that time, the pilots had taken manual control of the airliner.

"Airbus has advised that it is not aware of any similar event over the many years of operation of the Airbus," the ATSB said.

Operators of the A330 and A340 may select air data computers manufactured by Litton, or Honeywell. The fault appears confined to the Litton models, according to the ATSB.

FMI: Read The ATSB Release On Its Investigation, www.qantas.com