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CANBERRA - A global alert and new operating instructions have been sent to all Airbus A330-300 operators following confirmation that a computer fault caused a Qantas flight to suddenly nosedive above Western Australia.
The 200m plunge injured more than 70 of the 303 passengers and 10 crew, some seriously, and forced an emergency landing at Learmonth, in far north WA.
Learmonth is a remote Air Force "bare base" maintained by a skeleton staff for rapid deployment of strike jets in a crisis.
The emergency at 37,000ft aboard QF72 as it flew from Singapore to Perth on October 7 sparked international concern and speculation that laptops used by passengers may have triggered a malfunction in the airliner's flight computers.
But the preliminary report by the Australian Transport Safety Bureau has blamed a fault in one of the aircraft's three air data inertial reference systems, which process other data for the flight control computers commanding the elevators.
The findings were passed to the manufacturer, Airbus, which in turn has sent the information to all A330-300 operators, with new recommendations to help aircrew cope with any repeat.
More than 240 of the wide-bodied long-range airliners are flying with 29 airlines around the world.
Other major users include Cathay Pacific, China Airlines, Dragonair, Korean Air, Lufthansa, Malaysia Airlines, Northwest and Thai.
None has crashed.
ATSB investigation director Julian Walsh said the airliner contained very sophisticated and highly reliable systems, and the emergency aboard QF72 appeared to be unique.
Airbus had told the bureau it was not aware of any similar event in the 14 years the airliner had been in operation.
"These aircraft have been operating over many hundreds of hours over many years, and this type of event has not been seen before," he said.
Walsh also praised the Qantas pilots.
"The crew's timely response led to the recovery of the aircraft trajectory within seconds," he said. "During the recovery the maximum altitude loss was 650ft."
The bureau's investigation, which includes experts from its French equivalent, the Bureau d'Enquetes et d'Analyses, Airbus and the American National Transportation Safety Board, is continuing.
Investigators will analyse data from the three inertial reference systems, and will examine the units at the US manufacturing plant.
They will also scrutinise the aircraft's maintenance history, and interview passengers in a bid to fully understand what happened in the cabin when the airliner pitched into an 8.5-degree nosedive without warning.
Injuries included broken bones and lacerations.
Walsh said investigations so far indicated that a fault in one of the inertial reference units automatically disconnected the autopilot, feeding false data to the airliner's flight control primary computers.
These included false stall and overspeed warnings, loss of altitude on the captain's primary flight display, and several electronic centralised aircraft monitoring system warnings.
About two minutes after the initial fault, the unit generated very high, random and incorrect values for the airliner's angle of attack: the relationship between the aircraft and the airstream through which it is flying.
In response, the flight control computers ordered a dive, and continued to generate random "spikes" that led to a second, but less significant, nose-down aircraft movement.
"At this stage of the investigation, the analysis of available data indicates that the [inertial reference unit's] abnormal behaviour is likely as the origin of the event," Walsh said.
